Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A study of acorn feeding insects : filbert weevil (Curculio occidentis (Casey)) and filbertworm (Cydia… Rohlfs, Doris Andrea 1999

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_1999-0221.pdf [ 13.81MB ]
Metadata
JSON: 831-1.0099321.json
JSON-LD: 831-1.0099321-ld.json
RDF/XML (Pretty): 831-1.0099321-rdf.xml
RDF/JSON: 831-1.0099321-rdf.json
Turtle: 831-1.0099321-turtle.txt
N-Triples: 831-1.0099321-rdf-ntriples.txt
Original Record: 831-1.0099321-source.json
Full Text
831-1.0099321-fulltext.txt
Citation
831-1.0099321.ris

Full Text

A STUDY OF ACORN FEEDING INSECTS: FILBERT WEEVIL (Curculio occidentis (Casey)) AND FILBERTWORM {Cydia latiferreana (Walsingham)) ON GARRY OAK {Quercus garryana) (Dougl.) IN THE SOUTHEASTERN VANCOUVER ISLAND AREA by DORIS ANDREA ROHLFS B.Sc, The University of Victoria, 1995 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Forest Sciences Faculty of Forestry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1999 © Doris Andrea Rohlfs, 1999 In p resen t ing this thesis in partial fu l f i lment of t h e requ i rements for an a d v a n c e d d e g r e e at the Univers i ty of Brit ish C o l u m b i a , I agree that the Library shall m a k e it f reely avai lable fo r re fe rence a n d study. I further agree that p e r m i s s i o n f o r ex tens ive c o p y i n g o f this thesis fo r scho la r l y p u r p o s e s may b e granted by the h e a d of m y d e p a r t m e n t o r by his o r her representat ives . It is u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n of this thesis for f inancial gain shall no t b e a l l o w e d w i t h o u t m y wr i t ten p e r m i s s i o n . D e p a r t m e n t T h e Un ivers i ty of Brit ish C o l u m b i a V a n c o u v e r , C a n a d a D a t e D E - 6 (2788) ABSTRACT The Garry oak (Quercus garryana) Dougl. is the only oak native to British Columbia and is one of the more distinct and stately trees growing in the Greater Victoria area. The Garry oak meadow ecosystem is unique and rich, with the largest number of rare plant species of any ecosystem not only in British Columbia, but in Canada. Since acorns are vital to maintain future generations of Garry oak trees, the insects that attack and damage these acorns are of interest. Garry oak acorns were collected from June to September in 1996,1997 and 1998 to determine the abundance and spatial distribution of acorns infested by the filbert weevil (Curculio occidentis (Casey)) (Coleoptera: Curculionidae) and filbertworm {Cydia latiferreana (Walsingham)) (Lepidoptera: Olethreutidae) at 10 locations in the Greater Victoria area. The biology of C. occidentis was studied by laboratory rearings from 1997 through 1998. Both C. occidentis and C. latiferreana infested a large portion of acorns in 1996, 1997 and 1998, exhibiting an inverse trend of infestation level to crop abundance. This trend was more evident for the filbertworm, than the filbert weevil. Acorn crops in 1996 and 1997 were light, and in 1998 was heavy, a mast year. Dissection of 10,879 acorns showed the combined infestation rates by the two insects were 80.7%, 75.0% and 51.3% in 1996, 1997 and 1998, respectively. Of these acorns, the filbert weevil consistently infested more acorns than the filbertworm. Significantly more filbert weevil infested acorns occurred in the lower- than the middle- and upper-portion of the sample trees in 1998, but not in 1997. The proportion of acorns infested by the filbert weevil and filbertworm did not vary by compass direction (south, northeast and northwest) in either 1997 or 1998. Strata infestations were not examined in 1996. i i Although infestation by these two insects was high, it was shown that even moderately damaged acorns, with up to 50% damage to the cotyledon, still have the potential to germinate. In 1996,1997 and 1998, 51.4%, 49.5% and 77.6% of acorns, respectively, had less than 50% damage to the acorn cotyledon. Filbert weevil adults emerge in June through September to oviposit into the forming Garry oak acorns. Laboratory reared larvae feed, on average, for 5 Vi weeks, completing 4 larval instars during this time. The larvae overwinter in the 4th instar, and pupate in the spring. The pupal stage last approximately 12 days, with the callow adults requiring an additional 10.3 days to harden and gain full coloring. Females are larger than males in body length, body width, and rostrum length. Filbertworm eggs were rarely seen during this study. Larvae were observed in acorns beginning mid-July and emergence holes were found approximately one month later. Control measures for the filbert weevil and the filbertworm are not recommended because even moderately damaged acorns are capable of germinating. Thus, the impact of damage by these two insects is less than it appears. The natural cycle of poor and mast crops of Garry oak acorns acts as a natural control for these two insect populations. iii TABLE OF CONTENTS Page ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES ix ACKNOWLEDGEMENTS xii INTRODUCTION 1 STUDY OBJECTIVE 2 LITERATURE REVIEW 3 Garry oak Distribution and General Characteristics 3 Climate and Soils , 6 Acorn Biology 8 Acorn Production 8 Premature Abscission 10 Acorn Predation by Vertebrates 12 The Filbert Weevil and Filbert Worm 13 Filbert weevil 14 Filbertworm 15 MATERIALS AND METHODS 17 DESCRIPTION OF SITES 17 ACORN SAMPLING PROCEDURES 21 Weekly Sampling 21 Collection from Seed Traps 23 Strata Sampling 25 Mass Acorn Sampling 27 ACORN PROCESSING 28 Weekly and Strata Collections 28 Seed Traps... 30 Mass Collection 30 LARVAL REARING 33 1997 33 1998 34 ADULT COLLECTION OF WEEVILS 36 Adult Mating, Oviposition and Longevity 38 iv GERMINATION TESTS 40 1997 41 1998 42 STATISTICAL ANALYSIS 42 RESULTS 43 WEATHER 43 ACORN SIZE AND ABUNDANCE 46 INSECT DAMAGE 48 DAMAGE LOCATION ON ACORNS 52 INFESTATION RATES 52 TRAP CATCHES 67 Acorn Traps 67 Weevil Traps 67 STRATA SAMPLING 70 1997 70 1998 74 FILBERT WEEVIL BIOLOGY 78 Eggs 82 Larvae 82 Pupae 90 Adults 94 FILBERTWORM BIOLOGY 105 Eggs 105 Larvae 105 Pupae 114 Adults 114 GERMINATION TESTS 118 1997 118 1998 125 DISCUSSION 129 ACORN PRODUCTION AND INFESTATION 129 PROPORTION OF INFESTED ACORNS BY YEAR, SITE AND SAMPLE DATE 130 SEED TRAPS 133 ACORN VIABILITY 133 STRATA SAMPLING 136 FILBERT WEEVIL 137 FILBERTWORM 142 MANAGEMENT IMPLICATIONS 143 LITERATURE CITED 145 LIST OF TABLES Page Table 1. Sampling scheme, for the weekly-collected acorns, used at all 10 sites in 1996,1997, and 1998 22 Table 2. Classification of acorn damage (adapted from Swiecki et al. 1991) 29 Table 3. Parameters and measurements recorded during acorn processing of weekly and strata samples in 1996,1997 and 1998 31 Table 4. Mean length (mm) and width (mm) of acorns collected from weekly sampling from all 10 sites in 1996, 1997 and 1998 47 Table 5a. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for all acorns collected from all 10 sites in 1996 49 Table 5b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for infested acorns only collected from all 10 sites in 1996 49 Table 6a. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for all acorns collected from all 10 sites in 1996 50 Table 6b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for infested acorns only collected from all 10 sites in 1996 50 Table 7a. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for all acorns collected from all 10 sites in 1996 51 Table 7b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and filbertworm per acorn for infested acorns only collected from all 10 sites in 1996 51 Table 8. Percent of filbert weevil oviposition punctures, larvae and emergence holes in the distal, middle and proximal location of the weekly collected acorns at 10 sites in 1998 53 vi Table 9. Levels of infestation by the filbert weevil and the filbertworm by site and year based on weekly collections 55 Table 10. Results of one-way ANOVA: infestation of acorns by year for total infestation, filbert weevil, filbertworm and both insects 57 Table 11. Mean total infestation by the filbert weevil, filbertworm and both insects in 1996, 1997 and 1998 58 Table 12. Results of UNIANOVA: infestation of acorns for site, sample date and the interaction of site x sample date for the filbert weevil, filbertworm, both insects and total infestation in 1996 59 Table 13. Results of UNIANOVA: infestation of acorns for site, sample date and the interaction of site x sample date for the filbert weevil, filbertworm, both insects and total infestation in 1997 60 Table 14. Results of UNIANOVA: infestation of acorns for site, sample date and the interaction of site x sample date for the filbert weevil, filbertworm, both insects and total infestation in 1998 61 Table 15. Percent of acorns in each of the six damage categories in 1996, 1997 and 1998 66 Table 16. Mean number of healthy and non-viable acorns per trap, collected weekly from acorn traps at Mary Hill and Rocky Point in 1998 68 Table 17. Results of GLM: effects of insect infestation by level and direction for strata sampling in 1997 71 Table 18. Results of GLM: infestation of acorns by the filbert weevil and the filbertworm by level and direction for strata sampling in 1997 72 Table 19. Mean acorn infestation by strata level in 1997 73 Table 20. Results of GLM: effects of insect infestation by level and direction for strata sampling in 1998 75 Table 21. Results of GLM: infestation of acorns by the filbert weevil and the filbertworm by level and direction for strata sampling in 1998 76 Table 22. Mean acorn infestation by strata level in 1998 77 vii Table 23. Mean length and width of filbert weevil eggs 84 Table 24. Head capsule widths for the four larval instars of filbert weevil (1996,1997 and 1998 data combined) 89 Table 25. Duration of the four larval instars of the filbert weevil reared on artificial diet in the laboratory at 25°C in 1998 91 Table 26. Body size of female and male filbert weevil adults 95 Table 27. Number of filbert weevil adults collected by various methods in 1998 97 Table 28. Longevity of males and females reared in the laboratory both with and without food 98 Table 29. Longevity of male and female filbert weevils emerging in August, September and October/November 100 Table 30. Number of filbert weevil adults emerged from laboratory reared larvae emerged from August 5th to November 2nd 1998 102 Table 31. Date of emergence, oviposition and the number of eggs laid by filbert weevil adults in 1998 103 Table 32. Time elapsed from adult emergence to oviposition 104 Table 33. Significance of the variables weight and length in the regression equation for estimating damage in 1997 120 Table 34. Regression equation for estimating damage in 1997 121 Table 35. Proportion of the acorns germinating in the three damage classes in 1997 123 Table 36. Regression equation for estimating damage in 1998 126 Table 37. Proportion of the acorns germinating in the three damage classes in 1998 128 v i i i LIST OF FIGURES Page Figure 1. Present distribution of Garry oak ecosystems in south western Canada and the United States (modified from Stein 1990) 4 Figure 2. Present distribution of Garry oak ecosystems in British Columbia (modified from Coward 1992) 5 Figure 3. Sampling sites used for acorn collection in 1996,1997 and 1998 18 Figure 4. Acorn traps used at Mary Hill and Rocky Point 24 Figure 5. Strata levels of the crown of a sample tree 26 Figure 6. Proximal, middle and distal portions of an acorn 32 Figure 7. Head capsule showing the measurements taken: A-A' = length, B-B' = width (modified from Bedard 1933) ...35 Figure 8. Filbert weevil adult emergence trap (modified from Raney and Eikenbary 1969) 37 Figure 9. Monthly and 50 year mean minimum and maximum temperatures 44 Figure 10. Mean monthly precipitation for 1996,1997,1998 and the 50 year mean 45 Figure 11. Mean percent acorn infestation by the filbert weevil and filbertworm with all sites combined in 1996,1997 and 1998 54 Figure 12. Significant interactions between the ten sample sites by date and infestation by the filbert weevil, filbertworm, both insects and total infestation in 1996 62 Figure 13. Significant interactions between the ten sample sites by date and infestation by the filbert weevil, filbertworm, both insects and total infestation in 1997 63 ix Figure 14. Significant interactions between the ten sample sites by date and infestation by the filbert weevil, filbertworm, both insects and total infestation in 1998 64 Figure 15. Mean number of aborted and healthy acorns collected from acorn traps at Mary Hill and Rocky Point in 1998 69 Figure 16. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1996 79 Figure 17. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1997 80 Figure 18. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1998 81 Figure 19. Filbert weevil egg (pericarp is peeled away to expose egg) (10x) 83 Figure 20. Filbert weevil larvae (12x) 85 Figure 21. A) Early instar filbert weevil larva feeding (pericarp has been removed from acorn). B) Larva mining in lightly damaged acorn. C) Larva in moderately damaged acorn. D) Severely damaged acorn. Note: Both acorns B and C are beginning to germinate (2x) 86 Figure 22. Histogram of head capsule measurements of the filbert weevil in 1996,1997,1998 and all three years combined 87 Figure 23. Filbert weevil emergence hole (3x) 92 Figure 24. Dorsal and ventral view of a filbert weevil pupa (5x) 93 Figure 25. Male and female filbert weevil adults (6.5x) 96 Figure 26. Acorn damage caused by filbert weevil oviposition (10x) 101 Figure 27. Filbertworm egg (8x) 106 Figure 28. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1996 107 x Figure 29. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1997 108 Figure 30. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1998 109 Figure 31. Last instar filbertworm larva (5x) 110 Figure 32. Filbertworm emergence hole (3x) 112 Figure 33. Severe damage by the filbertworm. Frass and webbing fill the acorn (2.5x) 113 Figure 34. Histogram of head capsule measurements of the filbertworm combined from 1996,1997 and 1998 115 Figure 35. Filbertworm larva overwintering in cocoon (top) (3.5x) and filbertworm pupa (bottom) (7x) 116 Figure 36. Filbertworm adult (5.5x) 117 Figure 37. Height of Garry oak seedlings grown from healthy and light/moderately damaged acorns planted on November 1st, 1997 124 xi ACKNOWLEDGMENTS The completion of this research project was possible only through the efforts of many people. Dr. Imre S. Otvos provided financial support, laboratory, and office space for the duration of this study. I thank Imre for his direction and encouragement throughout the course of this study. I am very appreciative of my Committee members, Drs. John A. McLean and Antal Kozak who each contributed in complementary ways to this thesis. John McLean provided structure and focus to the project, and Antal Kozak always had time, and was patient with my statistical questions every time I came to his office. I thank Dr. Murray Isman for being the external examiner and providing thoughtful comments on my thesis. Many people assisted with field and laboratory work, and without their help, this project would not have been manageable. Robert Betts helped to collect acorns and build the field emergence traps. Weiling Mah, John Troung, Shannon Lee and Ralph Koglin all assisted with fieldwork. Meaghan Complin was invaluable in both the field and laboratory. Meaghan's help with acorn collection and processing, as well as insect rearing in the laboratory allowed me to process many more acorns and insects than I could have accomplished alone. I thank the Department of National Defense Environmental Science Advisory Committee for granting me access to Mary Hill and Rocky Point. I am grateful to the following people: Jamie McDuff (Environment Canada) for weather data, Rob Hagel (PFC) for assistance with all aspects of the greenhouse work, Barbara Hendel (PFC) for providing extensive library assistance and Tom Gray (PFC) who always had the tools I was looking for. I thank Andrea, Sharene, Line, Neil and Tim for their humor and friendship. My Mum, Dad and sister Monica have always been there for me. I thank them for their encouragement and support, not only during my thesis, but in all my endeavors. Last, but certainly not least, I thank Ray. Thank you for supporting and encouraging me, and always making me smile! xi i INTRODUCTION The Garry oak, Quercus garryana, Dougl. belongs to a unique ecosystem that has the largest number of rare plant species of any ecosystem, not only in British Columbia, but in Canada. Approximately 140 of British Columbia's plant species (6% of the total) are found only in these habitats (Erickson 1996). About 75% of the red (threatened and endangered) and blue listed (vulnerable) plant taxa (12.5% of the total) and about 50% of the yellow-listed (potentially vulnerable) taxa (about 20% of the total) occur in Garry oak communities (Erickson 1996). The Garry oak ecosystem has declined dramatically due to urban encroachment and invasions of exotic species and the remaining ecosystem is at risk (Meidinger and Pojar 1991, Erickson 1996). A loss of this ecosystem would reduce biodiversity in British Columbia. To maintain the present density of Garry oak trees and sustain this diverse ecosystem, crops of healthy acorns are needed. Insects, however, account for a reduction in the number and viability of acorns. Damage to acorns by insects, particularly weevils of the genus Curculio and the lepidopteran Cydia latiferreana, is widespread with reports of acorn infestation by these two insects ranging up to 100% (Korstian 1927, Downs and McQuilkin 1944, Gysel 1957, Brezner 1960, Gibson 1972, Beck 1977, Gibson 1982, Kaushal et al. 1993, and others). 1 In British Columbia, the insects causing damage to Garry oak acorns are the filbert weevil, Curculio occidentis (Casey) (Coleoptera: Curculionidae) and, to a lesser extent, the filbertworm, Cydia latiferreana (Walsingham) (Lepidoptera: Olethreutidae). Despite the importance of this tree as part of a diverse ecosystem and a unique part of the Victoria landscape, no research has been done on the amount of damage, or the impact on acorn germination these two insects have on Garry oak in British Columbia. Also, no data are available on the biology of the filbert weevil on Garry oak in British Columbia. There is a need for insect life history studies in order to begin to understand the dynamics of this ecosystem and the insects that are a part of them. STUDY OBJECTIVES The current study was initiated to: 1. Determine the proportion of Garry oak acorns infested by the filbert weevil and the filbertworm in the Greater Victoria area 2. Determine and examine the differences of acorn damage caused by the filbert weevil and filbertworm between years, site, and intra-tree infestations 3. Study the biology of the more damaging of these two insects 4. Ascertain the effects of insect damage on acorn germination. 2 LITERATURE REVIEW Garry Oak Distribution and General Characteristics Garry oak, Quercus garryana Dougl. (Fagaceae) is one of the more distinct and stately trees growing in the Greater Victoria area and is the only oak native to British Columbia (Sudworth 1908, Anonymous 1948, Harlow and Harrar 1968, Hosie 1973, Olson 1974). The range of Garry oak extends from southwestern British Columbia south into Oregon and northern and central California (Stein 1990) (Figure 1). In British Columbia, the Garry oak is restricted primarily to the southeast coast of Vancouver Island and the southern Gulf Islands. It is not found on the mainland except for two distinct stands, the first on Sumas Mountain and the second at Yale in the Fraser Canyon (Sudworth 1908, Glendenning 1944, Hosie 1973) (Figure 2). The distribution of Garry oak in British Columbia and Washington exists as fragmented stands, while further South in Oregon and California, Quercus garryana covers large continuous tracts of land (Bolsinger 1988). Meidinger and Pojar (1991) categorize Quercus garryana as common in the Coastal Douglas-fir (CDF) biogeoclimatic zone, very rare in the Coastal Western Hemlock zone, and absent in the remainder of the biogeoclimatic zones in British Columbia. The CDF in British Columbia is confined to elevations mostly below 150m and share similar climate and plant communities as those in Washington in the Puget Trough, San Jan Islands and in Oregon in the Willamette Valley (Franklin and Dryness 1973). 3 Figure 1. Present distribution of Garry oak ecosystems in south western Canada and the United States (modified from Stein 1990). 4 Figure 2. Present distribution of Garry oak ecosystems in British Columbia (modified from Coward 1992). 5 The Garry oak community can be classified as either Oak Parkland Type, or Scrub Oak - Rock Outcrop Type. The former occurs in the driest parts of the Victoria area where soils are relatively deep, but dry in summer (McMinn et al. 1976). These areas have abundant wildflowers in the spring with colorful (and native) blue camas (Camassia quamash (Pursh) Greene, and C. leichtlinii (Baker)), shooting star {Dodecatheon hendersoniiGray.), easter lily (Erythronium oreganum Applegate.), and chocolate lily {Fritillaria lanceolata Pursh.) (McMinn et al. 1976). Much of the original parkland, however, has been reduced by urban development, or the wildflowers are suppressed by invasive species such as scotch broom {Cytisus scoparius (L.) Link.). Some areas still exist, however, as parks and private property where spectacular bloom of the wildflowers can be seen in the spring. The Scrub Oak - Rock Outcrop Type is the second type of community where the oaks grow gnarled and stunted in shallow soil and rock outcrops and crevices (Sudworth 1908, McMinn et al. 1976). The wildflower display here is equally as impressive with yellow stonecrop (Sedum spathulifolium Hook.), wild onion (Allium cernuum Roth.), pink seablush (Plectritis congesta (Lindl.) DC.) and larkspur (Delphinium menziesii DC.) (McMinn et al. 1976). Climate and Soils The range of the Garry oak in British Columbia falls within a zone with a distinctly Mediterranean climate with summer drought and wet winters (Valentine et al. 6 1978). The Victoria area has a relatively dry climate as the CDF zone has developed in the rainshadow of Vancouver Island and the Olympic mountains where there is a gradient of decreasing rainfall from west to east (McMinn et al. 1976). Mean annual temperature ranges from 9.2 to 10.5°C with the monthly average of the daily minimum temperature rarely falling below 0°C (Nuszdorfer et al. 1991). Mean annual precipitation varies from 647 to 1,263 mm with only a small amount (about 5%) falling as snow (Nuszdorfer et al. 1991). The soils of Garry oak communities are dominantly Sombric Brunisol soils in the Victoria area and Humo-Ferric Podzol soils on the north east side of Vancouver Island and the Yale area (Valentine et al. 1978). Sombric Brunisol soils are acidic and have a relatively low base saturation. They occur typically under forest vegetation and are associated with Podzolic soils (Agriculture Canada Expert Committee on Soil Survey 1987). These soils are generally very wet in the winter because the soil does not freeze, and dry during the warm summer period (Valentine et al. 1978). The Humo-Ferric Podzol occurs only on coarse textured materials or on well drained sites and are generally strongly acidic (Valentine et al. 1978, Agriculture Canada Expert Committee on Soil Survey 1987). They occur typically under coniferous, mixed, and deciduous forest vegetation, but may also occur under shrub and grass vegetation (Agriculture Canada Expert Committee on Soil Survey 1987). 7 Acorn Biology Quercus garryana are dicotyledonous and monoecious, and the fruits are commonly called acorns. The male flower or catkin is odorless and insects are not attracted to them. Therefore, wind is the only means of pollination (Sharp and Chisman 1961). Female or pistillate flowers are produced on the same tree as the male catkins. The female flower, which is out before the leaves, can be either solitary or in two- to many- flowered spikes on the same tree (Olson 1974). The acorn contains one seed (rarely two) and has a straight embryo with no endosperm (Olson 1974). Acorns mature in 1 year and occur singly or in clusters up to five. The fruit is partially enclosed by a scaly cup and measures up to 37 mm in length. The shape of the acorn is subglobose to oblong, with a short point at the apex, and marked with a circular scar at their base, which is covered by the cup. Acorns are generally green then turn brown when ripe (Sudworth 1908, Anonymous 1948, Harlow and Harrar 1968, Hosie 1973, Olson 1974, Pojar & Mackinnon 1994). Acorn Production The most critical stage in the life history of plants is seed production since it contributes to recruitment and dispersal of progeny (Harper 1977). Seed production by Garry oak is extremely variable both among years, and within stands. One tree in a stand may bear copious acorns while another in the same stand produces none or only a light crop (Downs and McQuilken 1944, Sharp 8 and Sprague 1966, Beck 1977, Fenner 1991, Koening et al. 1994). Large acorn crops are referred to as 'mast seeding' or 'mast crop', and generally, a mast crop 1 year is followed by a long interval when few seeds are set (Ballardie and Whelan 1986). This interval may be one or more years but is completely unpredictable (Crawley 1992). Several hypotheses have been put forth to explain masting with the most popular being that large crops may satiate predators and dispersers and insure survival of at least some seed (Janzen 1971, Crawley 1992, Tapper 1992, Koening et al. 1994, Crawley and Long 1995). The predator satiation hypothesis predicts that trees should mast together in order to swamp predators in mast years, and starve them in non-mast years (Silvertown 1980, Waller 1993). Alternate hypotheses are that large crops attract dispersers (Crawley 1992) and a combination of large and small crops maintain predator and disperser populations while limiting their growth (Janzen 1971). Koening et al. (1994) investigated four hypotheses that may explain mast seeding: predator satiation, resource matching, seed dispersal, and wind pollination. Their observations only support the "wind pollination" and "predator satiation" hypothesis. Koening et al. (1994) points out, however, that no single ecological factor totally accounts for seed production. 9 Sharp and Chrisman (1961), Sharp and Sprague (1966) and Farmer (1982) all suggest that climatic factors are important in controlling flower formation and development, and pollination. Sharp and Sprague (1966) report that in years when April remained cool, followed by warm nights in May, acorn production was poor. However, when a warm April was followed by a cool May acorn set was good. No correlation was found between the quality and yield of acorn crops and humidity or precipitation. The theory that drought, even severe drought, reduces acorn yield was disproven (Sharp and Sprague 1966). It is known, however, that a late frost will 'sear' young oak shoots and leaves, resulting in destruction of the entire acorn crop (Farmer 1982). Goodrum et al. (1971) found no relationship between rainfall and seed production, and it was found that few trees below age 20 produced seeds (Reid and Goodrum 1957). Also, mast yields increased linearly with increased bole size and acorn yield increased with increased crown radius (Reid and Goodrum 1957, Goodrum et al. 1971). Heredity and other influences within an individual tree also contribute to fruiting potential. Trees with codominant or suppressed crowns in the canopy produce fewer good acorn yields than those with dominant crowns (Reid and Goodrum 1957). Premature Abscission Many acorns on Garry oak trees never reach maturity, and it is not only unpollinated flowers that will not develop into mature fruit. Several factors that may contribute to premature abscission of acorns (acorns that are not mature, non-viable and fall from the tree before mature acorns) include late frosts in the 10 spring and unusually high summer temperatures. It has also been suggested, however, that premature abscission is the result of an upper limit that is set and is determined by environmental resources, rather than the number of flowers, and that even if a flower is pollinated, it does not necessarily set fruit (Stephenson 1981). Some researchers believe that the inability of the fruit to obtain adequate resources promotes the production of growth inhibitors, which promote a fruit to abscise (Tamas et al. 1979). Others (Williamson 1966, Feret et al. 1982) have found that abscission occurs primarily during the period encompassing pollination and fertilization. Many plants can selectively abscise damaged fruits, or the plant may initially initiate more fruit than there are resources for and therefore abort the surplus fruit (Stephenson 1981). It has been reported that acorns infested by insects fall from the tree prematurely (Dohanian 1944, Armstrong 1958, Williamson 1966, Janzen 1969,1971, Bramlett 1972, Beck 1977, Boucher and Sork 1979, Matsuda 1982). It has also been documented that insect damage to very young fruit increases the likelihood of abscission and that the aborted fruit often has a significantly higher frequency of insect infestation (Janzen 1971, Boucher and Sork 1979, Stephenson 1981). It is not known if this early drop of fruit has evolved as a means of energy conservation by the host (Boucher and Sork 1979, Stephenson 1981, Matsuda 1982), is due to the breakdown of the normal physiological process of fruit development (Boucher and Sork 1979), or is the result of a 11 secondary infection due to the acorn being damaged by oviposition or insect feeding (Stephenson 1981). Acorn Predation bv Vertebrates Acorns are a very nutritious food for wildlife and are high in fat, carbohydrates, and contain protein, vitamins, calcium, and phosphorus (Forbes et al. 1941, Wainio and Forbes 1941, Menke and Fry 1980). Acorns are not only used as a food source for squirrels, but birds, deer and rodents rely on acorns as well (Nichol 1938, Downs 1944, Duvendeck 1962, Goodrum et al. 1971, Smith and Follmer 1972, Marquis et al. 1976, Bossema 1979, Menke and Fry 1980). Cypert and Webster (1948) reported that between 13 to 22 % of an acorn crop may be consumed by birds, and up to 54 % of the mast crop may be cached by squirrels (Darley-Hill and Johnson 1981). Downs and McQuilken (1944) reported that about 13% of the acorn consumption was by rodents whereas Marquis et al. (1976) found that rodent pilferage was extremely high. Some studies have shown that vertebrate seed predation is low in a year with an abundant seed crop and higher in a moderate crop year (Nilsson 1985). Others, (Howe and De Steven 1979, Howe and Smallwood 1982, Moore and Willson 1982, Stapanian 1982, Davidar and Morton 1986), however, reported that crop size did not influence the proportion of fruit removed. Consumption of insect-infested acorns by squirrels and other animals has been debated in the literature. Since food hoarding is critical to survival in many 12 animals, it is thought that the ability to distinguish between sound seeds and those that may perish easily or not provide sufficient nutrients (i.e. acorns whose cotyledons have been consumed by insects) is a trait that would be beneficial. Seed consumers are believed to reject infested seeds because of this reduced nutritional value, increased perishability, or even reduced palatability (Korstian 1927, Dennis 1930, Mailliard 1931, Janzen 1971, Sork and Boucher 1977, Bossema 1979, Sork 1987, Steele et al. 1996). Others, however, strongly suggest that animals are not able to distinguish between infested and sound seeds (Horton and Wright 1944, Semel and Anderson 1988, Weckerly et al. 1989a). Johnson et al. (1993) reports that since birds, such as blue jays {Cyanocitta cristata L), have no known physiological adaptation to counter the negative effects of acorn tannins on protein digestion, there may be some other way that the blue jays obtain enough protein to subsist. They suggested that blue jays might supplement their diet with weevil infested acorns to enable them to maintain their mass. Johnson et al. (1993) conclude that weevil larvae (or other insects) in the acorns counteract the effects of the high tannins in the jay diet and allow the jays to subsist mainly on an acorn diet in the fall caching season. The filbert weevil and filbertworm Both the filbert weevil and the filbertworm are primary invaders of acorns. Consumption of the acorn kernel containing the cotyledon and embryo by these 13 insects may result in reduced reproductive success for the oak. Although the life history for both Curculio occidentis and Cydia latiferreana is generally known outside of British Columbia, the details of the life history of these two insects on Garry oaks in B.C. is not known. Filbert weevil The filbert weevil, Curculio occidentis (Casey) (Coleoptera: Curculionidae) is a native pest to North America and is distributed from southern British Columbia south into Baja, California and can also be found in Arizona, New Mexico and Utah (Gibson 1969, Keen 1958). The filbert weevil was originally named Balaninus uniformis LeConte 1857, and then Balaninus occidentis Casey 1897. The first major revision was by Chittenden (1927) who replaced the generic name Balaninus Germar with Curculio Linnaeus. The weevil was renamed Curculio uniformis (LeConte) in 1927 and then Curculio occidentis (Casey) (Gibson 1969). The filbert weevil has been known to feed on Castanopsis chrysophylla (Dougl.) (giant chinkapin), Corylus californica (hazelnuts), Quercus. chrysolepis (canyon live oak), Q. garryana Dougl. (Oregon white oak), Q. kelloggiiNewb. (California black oak), Q. lobata (California white oak), and Q. sadleriana (sadler oak) (Gibson 1969). 14 The generalized life cycle of C. occidentis is as follows. In the spring, the female filbert weevil uses her rostrum to chew a hole into a developing acorn and inserts an egg into the hole with her ovipositor. The larvae hatch inside the acorn and start to feed on the acorn kernel. After completion of feeding, the last instar larva chews an exit hole through the acorn shell, and burrow into the ground where they overwinter as last instar larva. In spring the larvae pupate, and emerge as adults shortly thereafter (Gibson 1969, Kearby et al. 1986). Parasitoids of the filbert weevil are not abundant due to the cryptic location of the eggs and larvae. However, parasitoids of the genus Urosigalphus (Braconidae) and of the genera Myiophasia and Cholomyia (Tachinidae) (Brooks 1910, Muesbeck et al. 1951, Gibson 1969, Kearby et al. 1986) have been reared from the filbert weevil. Filbertworm The filbertworm, Cydia latiferreana (Walsingham) (originally Melissopus latiferreana (Riley)) (Lepidoptera: Olethreutidae: Laspeyresiinae) is also a native pest to North America and is distributed throughout southern Canada and the US (AliNiazee, 1980). In addition to oak acorns, the larvae have been found in wild hazelnuts (Corylus spp.), apricots (Prunus spp.), chestnuts {Castanea spp.) and walnuts (Juglans spp.) (AliNiazee, 1980). 15 The filbertworm is a univoltine insect that overwinters in the larval stage in the soil (AliNiazee, 1983). The adult emerges from mid-June through September. After mating the female lays eggs singly on the acorn or cup bract and after hatching the larvae work their way up between the cap and the nut to enter through the micropyle (Passon 1990). The larvae complete feeding in about 3 weeks, and they then leave the acorn by chewing an exit hole; they hibernate in the soil within their cocoons. Pupation takes place the following spring and the pupal period lasts about 1 month (Dohanian 1940, Pucat 1994). Six species of parasitoids have been reared from the filbertworm, all in very low numbers. The egg parasitoid Trichogramma evanescens Westwood (Trichogrammatidae), the four larval parasitods Elachertus evetriae Girault (Eulophidae), Macrocentrus ancylirorus Roh. (Braconidae), Phanerotoma tibialis (Hald.) (Braconidae), a Lissonata Cushman (Ichneumonidae) species and a pupal parasitoid of the Phorocera (Coq.) (Tachinidae) species (Thompson 1938, Dohanian 1940). 16 MATERIALS AND METHODS DESCRIPTION OF SITES The study was conducted from May to October in 1996,1997, and 1998 in the Greater Victoria area. Ten study sites were selected in May of 1996 and the same sites were used for acorn collections during the 3 years of the study. The 10 study sites used were: Mary Hill, Rocky Point, Officers' Mess, High Rock Park, Beacon Hill Park, Summit Park, Playfair Park, Mt. Tolmie, Christmas Hill and Layritz Park (Figure 3). Site 1 - Marv Hill Mary Hill is located in Metchosin (about 30 km south of Victoria) on Department of National Defense (DND) land. The study area is approximately 10 ha in size. The site is located on a south-facing slope, with a mixed Douglas-fir {Pseudotsuga menziesii (Mirb.) Franco) and arbutus {Arbutus menziesii Pursh) stand surrounding the Garry oak site. Scotch broom {Cytisus scoparius (L.) Link.) is very common and covers the majority of the study area. Human disturbance is limited at this site because it is fenced, and a permit and key are required to access the area. Site 2 - Rocky Point Rocky Point is about 2 km from Mary Hill and is also located on DND land. The 10 ha area is relatively flat with patches of scotch broom. The Garry oak meadow at Rocky Point is sheltered from the ocean by a mixed Douglas-fir, 17 18 arbutus, grand fir (Abies grandis (Dougl.) stand. As with Mary Hill, a permit is required to access the fenced area and, therefore, disturbance is limited. Site 3 - Officers' Mess Officers' Mess is a small stand of approximately 30 Garry oak trees in the Esquimalt area. The location is not a very high use area and scotch broom is limited. Site 4 - High Rock Park High Rock Park is also in Esquimalt and is a rocky, high use park, adjacent to a school and soccer field. Site 5 - Beacon Hill Park Beacon Hill Park is situated in the heart of down town Victoria and is the highest use area of all 10 locations. The park is multi purpose with jogging and walking trails. Sprinklers irrigate some trees in the park, but none of these trees were used in the study. Site 6 - Summit Park Summit Park is located in central Victoria is a moderately use park with a few well-used trails. Scotch broom is minimal in this area. Site 7 - Plavfair Park This is a high use park adjacent to a playground and playing field. There is very little scotch broom in the area. 19 Site 8 - Mt Tolmie Mt. Tolmie is an 18 ha park near the University of Victoria with well-established trails that see very high use. Scotch broom is a problem but recent efforts to eradicate it by manual means have opened up the area to a more "natural" state. Scotch broom continues to regenerate quickly, however, and broom pulling is an on-going project. Site 9 - Christmas Hill Christmas Hill was, until a few years ago one of the most undisturbed sites of this study but unfortunately over the last 2 years, urban encroachment has pushed the city limits to the doorstep of this area. A few oaks have been felled on the fringes of Christmas Hill and condominiums and town houses now surround what was a quaint hill overlooking Victoria and the surrounding areas. Site 10- Lavritz Park Layritz Park is a very high use area with two baseball fields and a paved/gravel parking lot. The oaks are around the baseball fields, and a few are scattered in a gravel parking lot. The soil is very compacted next to the oaks around the baseball diamonds as well as the ones in the parking lot. 20 ACORN SAMPLING PROCEDURES Acorns were sampled in four ways: 1. once a week for 15 weeks 2. by seed traps 3. by crown strata 4. by mass collection Weekly Sampling The weekly sampling was a repeated measures design. Weekly collections were started on June 22nd 1996, June 24th 1997 and on June 23rd 1998 when the young acorns had begun to develop. The sampling continued for a total of 15 weeks each year. Each year at each of the 10 study sites, 15 sample trees, with crowns accessible with a telescoping pole pruner and developing acorns, were selected for sampling. Each tree was labeled with a plastic number tag at the base and the location of the tree recorded on a sketch map of the area. The same trees were not sampled every year since acorn production on Garry oak trees is so variable from year to year that trees with acorns in 1996, did not necessarily have acorns in 1997 or 1998. The 15 Garry oak trees were divided into three subgroups of five trees each. Each week, one tree from each subgroup was sampled for a total of three trees sampled each week from each location. All of the 15 trees were sampled in 5 weeks and the sampling then started all over again with tree number 1 (Table 1). 21 Table 1. Sampling scheme, for the weekly collected acorns, used at all 10 sites in 1996, 1997 and 1998 Week Tree number sampled 1 1,2,3 2 4, 5,6 3 7, 8,9 4 10, 11, 12 5 13, 14, 15 6 1,2,3 7 4, 5,6 8 7,8,9 9 10, 11, 12 10 13, 14, 15 11 1,2,3 12 4,5,6 13 7, 8,9 14 10, 11, 12 15 13, 14, 15 22 Ten acorns were collected from each of the three sample trees on each collection date. Branch tips were located that contained acorns, and from the acorn bearing branches, a tip was clipped from the tree using a telescoping pole pruner. The acorns were removed from the foliage, placed into labeled plastic bags and stored at 4°C at the Pacific Forestry Centre (PFC) until processed. Collection From Seed Traps Three traps were placed under each of 12 Garry oak trees at both Mary Hill and Rocky Point. The traps were emptied weekly in 1998 and at the end of the collection season in 1997. The acorn traps were obtained from another researcher who studied seedling ecology of Garry oaks and dispersal of Garry oak acorns by Steller's jays (Fuchs 1998). The traps were constructed with a wire basket and a plastic insert with a fiberglass bag (Figure 4). Each trap had a collecting surface area of 0.25 m2. The traps were staked into place under sample trees with a 2 m metal stake. The plastic insert on the traps was intended to discourage rodents and other animals from entering the traps and removing the acorns. 23 Figure 4. Acorn Traps at Mary Hill and Rocky Point. 24 Strata Sampling The spatial distribution of insect infested acorns within the crown of Garry oak trees was determined in 1997 and 1998 using a 3x3 factorial experiment. Nine sampling strata per tree were vertically aligned into blocks of three (lower-, middle- and upper-crowns), their centers each facing a different compass direction. The three compass directional designations were Northeast, South and Northwest (Figure 5). Each of the nine segments is referred to as a stratum. This design was used by other investigators (Boethel et al. 1974, Lewis 1992) and was followed in this study to allow the comparison of results. The following criteria were used for choosing sample trees: 1. The tree had to be reachable with a telescoping pole pruner 2. The tree had to have developing acorns and 3. Branches and acorns were present in all nine strata. A randomized complete block design was used in which each tree was the block, and acorns were collected from all nine strata from each of the sample trees. Ten acorns were collected randomly from each strata level from as many trees that could be found that fit the three sampling criteria above. This resulted in an unequal number of trees being sampled, and therefore the data was analyzed using a General Linear Model (GLM). 25 Figure 5. Strata levels of the crown of a sample tree. 2 6 Mass Acorn Sampling Mass collections of acorns were made by locating trees that had produced acorns that year, and collecting acorns off the ground from under 10-15 trees at each site in both 1997 and 1998. Mass collected acorns were used to accomplish objectives 1, 2 and 3 in 1997, while in 1998 acorns were used only for objectives 2 and 3. Objectives of mass acorn collection: 1. To provide a supply of weevil larvae for rearing and making observations on weevil biology and behavior 2. To determine a regression equation to estimate insect damage from acorn length and weight 3. To provide a supply of acorns to investigate the effect of insect damage on germination Due to a poor acorn crop in 1997, acorns could only be mass collected from three locations (Summit Park, Officers Mess, and Playfair Park). Approximately 1,000 acorns were collected from each of the three sites. In 1998, approximately 500 acorns were collected from each of Playfair Park, Christmas Hill, Officers' Mess, High Rock Park, Beacon Hill Park, Summit Park and Layritz Park. Mass collected acorns were placed in plastic bag, labeled and stored at PFC in a refrigerator at 4°C for about 2 weeks, and then processed. 27 ACORN PROCESSING Weekly and Strata Collections After weekly and strata acorn collections were finished, the acorns were taken to the laboratory and stored in a plastic bag in a refrigerator at 4°C until the acorns were processed, usually the next day. All data from the processing was entered into a hand held data logger (Pplycorder - Omnidata International Inc.). During acorn processing the length and width of each acorn was measured using an electronic caliper (Digimatic: Mitutoyo Corporation). Each acorn was examined for the presence of filbert weevil oviposition punctures, filbertworm feeding, or emergence holes of both the filbert weevil and the filbertworm. If any weevil oviposition punctures were found, the pericarp of the acorn was peeled away around the puncture to determine the presence of eggs. The number of eggs was recorded and the eggs were either preserved in 70% EtOH in 1996 and 1997 or removed with feather forceps and placed on artificial diet for rearing in 1998. After the external examination of the acorn, each acorn was cut open lengthwise using a cone cutter and the kernel of the acorn was examined for insect damage. Insect feeding and damage was estimated using the scale developed and used by Swiecki et al. (1991) where 0 = no damage and 6=>97.5% damage (Table 2). 28 Table 2. Classification of acorn damage (adapted from Swiecki et al. 1991) Damage Class Percent Damage 0 None visible 1 Trace to 2.5 2 >2.5 to 20 3 >20 to 50 4 >50 to 80 5 >80 to 97.5 6 >97.5 29 Filbert weevil and filbertworm larvae present in acorns in 1996 and 1997 were removed and preserved in 70% EtOH. In 1998, weevil larvae were placed on artificial diet for rearing. Preserved larvae were stored until head capsule measurements could be taken. In 1998 acorns were processed in the same manner as in 1997 except nine new categories were added to indicate the location of weevil oviposition holes, weevil eggs, weevil larvae, and weevil emergence holes on the acorn (Table 3). The position of each damage mark was recorded as; proximal, middle or distal (Figure 6). Seed Trap Acorns that were collected from seed traps were brought back to the laboratory and stored at 4°C until they were processed. The acorns were classified into two categories: healthy acorns and non-viable (aborted) acorns. The number of acorns in each category was recorded. Mass Collection Mass collected acorns were brought to the laboratory where they were stored at 4°C until use. In 1997 the acorns were set up for larval rearing (see Methods: Larval rearing 1997) and the acorns were processed for germination tests in both 1997 and 1998 (see Methods: 1997 & 1998 Germination tests). 30 Table 3. Parameters and measurements recorded during acorn processing weekly and strata samples in 1996,1997 and 1998 Category Category used in 1996* 1997 1998 Date Location Tree Acorn number Length of acorn Width of acorn No. of filbert weevil oviposition holes/acorn No. of filbert weevil eggs/acorn No. of filbert weevil larvae/acorn No. of filbert weevil emergence holes/acorn No. of filbertworm eggs/acorn No. of filbertworm larvae/acorn No. of filbertworm emergence holes/acorn Damage category No. of oviposition holes in distal portion of acorn No. of oviposition holes in middle portion of acorn No. of oviposition holes in proximal portion of acorn No. of emergence holes in distal portion of acorn No. of emergence holes in middle portion of acorn No. of emergence holes in proximal portion of acorn No. of larvae in distal location portion of acorn No. of larvae in middle location portion of acorn No. of larvae in proximal location portion of acorn / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / * strata samples were not collected in 1996 31 Figure 6. Proximal, middle and distal portions of an acorn. 32 LARVAL REARING 1997 Filbert weevil larvae obtained from mass collected acorns were reared to adults to provide information on their biology. Due to low numbers of filbertworm larvae, and time constraints, filbertworm larvae were not reared: Mass collected acorns were used to provide a supply of weevil larvae. The mass collected acorns were placed in ice-cream buckets filled Vfe to % full of clean sand obtained from the PFC greenhouse, and left on the sand from October 6th to November 7th 1997 (33 days) until the larvae had emerged from the acorns and burrowed into the sand. Sand was used as overwintering medium for the weevil larvae because it was found by others to provide the highest rate of survival (80% to 95%) for overwintering weevil larvae of the genus Conotrachelus (Gibson 1964). The buckets with the weevil larvae in the sand were transferred to a shade house at PFC on November 10th 1997 where they were kept at ambient temperature. The buckets were periodically moistened and left in the shade house until the adults started to emerge in August 1998. In early February of 1998,175 last instar filbert weevil larvae were removed from the sand from the buckets and placed individually in glass vials filled with sand. Larvae were manipulated so that they would be in contact with the sides of the 33 vials to allow observation. The vials with the larvae were placed in small boxes with a lid to simulate darkness, and placed in the shade house along with the buckets. Observations were made daily and the date of pupation, duration of the pupal stage, and adult emergence recorded. 1998 In 1998 filbert weevil eggs and larvae, collected from weekly collected acorns were reared to determine the number of successive instars and duration of each larval instar (as well as length of egg stage). Each egg and/or larva that was removed from the acorn was placed individually into a plastic creamer cup (3/4 ounce, Portion Packaging Inc.) containing artificial diet (Bio-Serve Inc. 1997). Eggs and larvae were held at 25°C, 50% RH, and L: D 14:10. The eggs were observed daily and the time required for each egg to hatch was recorded. Larvae were placed in a divot made in the diet with forceps so that the larvae would be able to get a purchase on the diet. Larvae were transferred to new diet when the diet became dry or showed signs of microbial contamination. Larvae were examined three times weekly and the feeding tunnels examined for cast skins. When a cast skin was found in the diet, a head capsule measurement was made on the live larva. The head capsules of the successive larval stage were measured (width (mm) and length (mm)) (Figure 7) using a stereomicroscope (Wild-M5) with electronic ocular micrometer (Microcode II). Dyar's rule was applied to the data and the duration of instars was determined by plotting the head capsule width as a histogram. 34 Figure 7. Head capsule showing the measurements taken: A - A' = length, B - B' = width (modified from Bedard 1933). 35 Dyar (1890) was the first to recognize that the number of instars that a larva passes through is characteristic of a given species and stated that "widths of the head of a larva in its successive stages follow a regular geometric progression." The number of peaks in the histogram was used to determine the number of instars. ADULT COLLECTION OF WEEVILS Adult filbert weevils were collected in 1998 by beatings, from emergence traps, and from larval rearing in 1997. Beatings were conducted by placing a canvas sheet (1.5 x 2 m) under the branches of a Garry oak tree and hitting the branches repeatedly with a 3 meter pole. Weevils were collected as they were dislodged from the foliage and fell onto the sheet. The emergence trap used was a modification of a trap designed by Raney and Eikenbary (1969). Each trap was constructed from four 70.5 cm by 5cm by 5cm boards fastened into a square for a collecting area of 0.5m2. An insect screen (Bay Mills 0.028 mm diameter mesh) was held into a pyramidal shape with copper welding rods. A wooden ring was fastened to the top of the rods with a clamp and a collecting jar inserted into the wooden ring (Figure 8). One trap was placed under the crown of each of twelve sample trees at each of four locations (Mary Hill, Rocky Point, Summit Park and Christmas Hill). 36 Figure 8. Filbert weevil adult emergence trap (modified from Raney and Eikenbary 1969). 37 Sand was poured around the base of each trap to fill any cracks that occurred between the ground and the base of the trap. The traps were placed under the crown of trees with the highest filbert weevil infestation in 1997. Adult weevils were also collected in 1998 from the sand filled buckets that were seeded with weevil larvae from infested acorns in the fall of 1997. Buckets were checked daily for adult emergence starting on March 1, 1998. Adult Mating. Oviposition and Longevity Adult weevils obtained through field collection, or from laboratory rearing, were used to study oviposition habits and longevity. Unmated weevils of known age were placed individually in petri dishes and sexed according to the key by Gibson (1969). The main characteristics used to sex the adults were: - the rostrum - relative length, and angle of juncture with the head; rostrum of female abruptly inserted into head; male rostrum gradually merging with frons - Pygidium - male densely covered with long hairs extending beyond elytra; female with few or no hairs - Abdominal sterna -1 and 2 concave in male; convex in female: 5 concave in middle 1/3 in female; flat to slightly concave in middle 1/2 in male 38 Four groups of adults (unmated males, unmated females, pairs or groups) were confined to acorn clusters (3 per day) in oviposition chambers. Oviposition chambers consisted of a 2.25L white plastic bucket with lid (Pro-Western Plastics Ltd.). Two 6.5 cm holes were drilled in each side of the bucket and one in the lid and the holes covered with an aluminum insect screen (Bay Mills, 0.028mm diameter mesh). The number of weevils caged daily depended on the number emerging from the soil, with emergence and caging beginning on August 5th 1998 and continuing until November 2nd 1998. The weevils were transferred to new acorn clusters every 2n d day along with a damp piece of cheesecloth to provide moisture. Acorn clusters were examined to ensure there were no oviposition punctures already present before caging the weevils with the acorns. If puncture marks were present on the removed acorns, they were dissected and examined to confirm oviposition and to record the number of eggs deposited. Weevil longevity was measured from the day of emergence from the soil until the day of death. When adults died, they were pinned and body length, body width, and the length of the rostrum recorded. One group of weevils was not fed any acorns to determine the differences (if any) in longevity between weevils supplied with a continuous source of fresh food and those without. 39 In early September when the supply of green acorns became scarce, mature acorns were substituted as food for the adults in rearings. Since the shell on the acorns had hardened by September, the acorns were cut in half lengthwise and placed cut side up so that the adults would be able to oviposit into the kernel of the cut acorns easier than through the tough brown shell of the mature acorns. GERMINATION TESTS To estimate the amount of damage done to an acorn by insect feeding without dissecting the acorn, a regression equation was developed both in 1997 and 1998 based on acorn weight and length as the independent variables and damage class as the dependent variable. Each year approximately 1,500 acorns were chosen randomly from a sample of approximately 5,000 acorns and measured for both weight and length. The acorns were dissected and classified, based on the amount of insect feeding and damage to the acorn kernel, into four groups; healthy (no damage), light damage (trace-20%), moderate damage (21%-50%) and severe damage (>50%). Using the length, weight and damage class data of the acorns, a regression model was developed that incorporated the length and weight as independent variables and damage rating as the dependent variable. In both the 1997 and 1998 collections no significant difference was found between the light and 40 moderate damage classes and therefore these two classes (light and moderate) were combined to form the new light/moderate damage category. The model was then applied to a second random sample of acorns (from the same mass collected acorn sample as the acorns from which the model was determined) where weights and length was measured but the acorn was not cut open. The three damage categories were estimated from the weight and length measurements using the regression equation. 1997 The method chosen to test acorn germination in 1997 was to plant acorns and compare the number of acorns that successfully germinated and grew into young seedlings. Ninety acorns were chosen randomly from each of the three categories and planted in styroplugs (Ventblock®45 (615A) (45 cavity block at 336 ml per block) Beaver Plastics Ltd.) by the method used by PFC staff. The acorns were kept at ambient temperature inside the header house at PFC and were watered regularly by the greenhouse staff. Acorns were checked at weekly intervals for germination and the date of germination and size of the seedling recorded. Seedlings were monitored for 11 months. 41 1998 Due to time constraints in 1998, a faster method of testing the germination potential of the acorns was needed. The method chosen was one used by Bonner (1984) and Bonner and Vozzo (1987). This method is similar to the techniques used for official seed testing for acorns (Association of Official Seed Analysts 1978). The germination procedure developed by Bonner (1984) is as follows: 1. Cut acorn in half (cross section), and discard half with the cup scar 2. Peel the pericarp from the remaining half and place cut side down on a moist blotter paper 3. Incubate at 25°C with photoperiod LD 8:16 for 28 days 4. Count the total number of acorns that have germinated within 28 days. An acorn is scored as germinated if both radicle and shoot exhibit growth One hundred acorns from each of the three damage categories were tested in this manner, and total number of acorns germinated recorded. STATISTICAL ANALYSIS Statistical analysis was conducted using the statistical program SPSS (version 9, 1998). 42 RESULTS During the study, from June 1996 to March 1999, a total of 10,879 acorns were collected and processed from weekly sampling, 2,520 from strata sampling, 886 from acorn traps and approximately 10,000 from mass collections. All the acorns collected for the weekly and strata samples were measured for length and width, and dissected to determine insect infestation and feeding damage. A total of 300 filbert weevil larvae and 594 filbert weevil adults were reared in the 1998 season. No filbertworm adults were reared. WEATHER The mean monthly maximum and minimum temperature for the Greater Victoria area as well as mean monthly precipitation (including snow) was calculated using daily weather data provided by Environment Canada. Mean monthly temperatures (both minimum and maximum) were similar in 1997 and 1998 (Figure 9). In 1996, however, there was a sharp rise in mean temperature for April, and then an average (based on the 50 year mean) May. December was also unseasonably cool. Monthly precipitation in 1996,1997, 1998 and the 50-year mean are shown in Figure 10. 43 1996 max 1997 max 1996 max 50yearm3anmax 1996 rrin 1997 rrin 1998rrin •50yearrrEanrrin i i i r i i i i i i C .O -C = ^ 0 _ ^ CD > O Month Figure 9. Monthly and 50 year mean minimum and maximum temperatures. 44 Figure 10. Mean monthly precipitation for 1996,1997,1998 and the 50 year mean. 45 ACORN SIZE AND ABUNDANCE The mean length and width of acorns as measured by electronic calipers in 1996 compared to those in 1997 did not differ significantly (p < 0.05), while in 1998 the mean length and width of acorns was significantly (p<0.05) larger than the two previous years (Table 4). The size differential of the acorns correlates to the relative abundance of the acorn crop in 1996,1997, and 1998. Acorn abundance was estimated visually each year, and production in 1996 was a very poor, while 1997 was only slightly better. The acorn crop in 1998 was very heavy with an abundance of acorns, and is considered to be a mast-seeding year. 46 Table 4. Mean length (mm) and width (mm) of acorns collected from weekly sampling from all 10 sites in 1996,1997 and 1998 Dimension year n min max mean Std. Error Length 1996 2,408 3.69 30.74 13.86a1 0.09 1997 4,081 3.21 36.91 13.02a 0.08 1998 4,390 4.17 35.83 17.60b 0.01 Width 1996 2,408 3.91 26.79 13.77a 0.05 1997 4,081 4.92 24.96 13.82a 0.05 1998 4,390 5.73 26.38 15.58b 0.05 1 Means within dimensions followed by the same letter not significantly different. Bonferroni Test, P<0.05 47 INSECT DAMAGE The presence of insect damage (i.e. oviposition punctures, eggs and emergence holes) and insect larvae were calculated in two ways. The first gives the mean number of filbert weevil and filbertworm damage and larvae, by year, for the entire population of acorns that were dissected (Tables 5a, 6a and 7a), and the second gives the mean number of filbert weevil and filbertworm damage and larvae for the infested acorns only (Tables 5b, 6b and 7b). The maximum number of weevil oviposition holes found on one acorn was 16 (1996) and the maximum number of eggs found in one acorn was 19 (1996). The highest number of filbert weevil eggs found under one oviposition hole was six. Ten filbert weevil larvae were the maximum found in one acorn and four emergence holes were the highest number in one acorn (1996). The maximum number of filbertworm larvae in one acorn was five (1997) and the highest number of filbertworm emergence holes in one acorn was four (1997). Each year, the mean number of eggs per acorn was significantly higher (p<0.05) than the mean number of larvae or emergence holes, indicating high egg mortality. The mean number of larvae and emergence holes, however, did not vary significantly, indicating larval mortality inside the acorn is low (Tables 5b, 6b and 7b). 48 Table 5a. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for all acorns collected from all 10 sites in 1996 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 2,413 0 16 1.15 0.04 3.42 eggs 2,413 0 19 0.65 0.03 2.30 larvae 2,413 0 10 0.07 0.08 0.15 emergence holes 2,413 0 4 0.06 0.01 0.07 Filbertworm larvae 2,413 0 4 0.22 0.01 0.25 emergence holes 2,413 0 2 0.09 0.01 0.09 Table 5b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for infested acorns only collected from all 10 sites in 1996 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 1,126 0 16 2.44 0.06 4.17 eggs 1,126 0 19 1.39 0.06 3.90 larvae 1,126 0 10 0.15 0.02 0.32 emergence holes 1,126 0 4 0.13 0.01 0.15 Filbertworm larvae 677 0 4 0.78 0.03 0.46 emergence holes 677 0 2 0.33 0.02 0.25 49 Table 6a. Mean number of oviposition punctures eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for all acorns collected from all 10 sites in 1997 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 4,081 0 15 0.59 0.02 1.46 eggs 4,081 0 16 0.38 0.02 1.03 larvae 4,081 0 8 0.12 0.007 0.24 emergence holes 4,081 0 3 0.07 0.004 0.07 Filbertworm larvae 4,081 0 5 0.11 0.006 0.01 emergence holes 4,081 0 4 0.06 0.004 0.07 Table 6b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for infested acorns only collected from all 10 sites in 1997 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 1,345 0 15 1.79 0.04 1.52 eggs 1,345 0 16 1.17 0.04 1.49 larvae 1,345 0 8 0.37 0.02 0.79 emergence holes 1,345 0 3 0.20 0.01 0.45 Filbertworm larvae 662 0 5 0.72 0.03 0.44 emergence holes 662 0 4 0.42 0.02 0.29 50 Table 7a. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for all acorns collected from all 10 sites in 1998 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 4,362 0 8 0.51 0.02 0.94 eggs 4,362 0 10 0.25 0.01 0.52 larvae 4,362 0 10 0.14 0.009 0.38 emergence holes 4,362 0 4 0.05 0.005 0.09 Filbertworm larvae 4,362 0 3 0.03 0.003 0.04 emergence holes 4,362 0 2 0.03 0.003 0.03 Table 7b. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil and the filbertworm per acorn for infested acorns only collected from all 10 sites in 1998 Damage No. Min Max Mean Std. Error Variance Filbert weevil oviposition punctures 1,322 0 8 1.68 0.03 1.11 eggs 1,322 0 10 0.83 0.03 1.12 larvae 1,322 0 10 0.46 0.03 1.11 emergence holes 1,322 0 4 0.18 0.01 0.29 Filbertworm larvae 243 0 3 0.62 0.04 0.35 emergence holes 243 0 2 0.47 0.04 0.31 51 DAMAGE LOCATION ON ACORNS The location of filbert weevil oviposition punctures, larvae, and emergence holes were recorded for each acorn processed from the weekly-collected samples in 1998. A significant (p<0.05) number of oviposition holes (76.80%), larvae (55.56%) and emergence holes (44.62%) were found in the middle region of the acorn (Table 8). Larvae and oviposition punctures were recorded least often in the distal end of the acorn, and emergence holes least often in the proximal end. INFESTATION RATES Overall infestation levels at each study site were calculated using data from the weekly collected acorns starting from August 26th. This was done because there was a sharp rise in infestation rates from June until mid-August (Figure 11) and including the earlier dates would have decreased the true total overall infestation. Mean total (overall) infestation rates for 1996,1997 and 1998 were 80.7%, 75.1% and 51.3%, respectively. The highest total infestation rate, for all sites and years, was 91.4% at Christmas Hill in 1996 and the lowest was 24.3% at Rocky Point in 1998 (Table 9). In all cases, for all locations, total infestation was the lowest in 1998 and in all cases except two (Rocky Point and Mt. Tolmie) 1996 had the highest overall infestation. 52 Table 8. Percent of filbert weevil oviposition punctures, larvae and emergence holes in the distal, middle and proximal location on the weekly collected acorns at all 10 sites in 1998 Location on Acorn n Oviposition Punctures Larvae Emergence Holes Distal 4391 3.29a1 6.37a 29.54a Middle 4391 76.80c 55.56c 44.62b Proximal 4391 19.91b 38.07b 25.85a 1 Means within oviposition punctures, larvae and emergence hole categories, followed by the same letter not significantly different. Bonferroni, P<0.05 53 100 Col lect ion Date Figure 11. Mean percent acorn infested by the filbert weevil and filbertworm with all sites combined in 1996, 1997 and 1998. 54 Table 9. Levels of infestation by the filbert weevil and the filbertworm by site and year based on weekly collections Percent Infestation Location Year n Filbert weevil Filbert worm Both Total Mary Hill 1996 175 42.52 41.95 11.81 72.67 1997 190 32.32 39.73 3.29 68.76 1998 210 43.81 10.95 2.89 51.90 Rocky Point 1996 170 41.96 9.22 2.94 48.24 1997 210 42.48 10.85 1.90 51.43 1998 210 20.95 3.33 0.00 24.29 Officers' Mess 1996 180 58.10 40.23 13.19 85.14 1997 200 44.27 21.10 3.40 61.97 1998 210 38.57 4.29 1.90 40.95 High Rock Park 1996 175 55.62 49.43 16.62 88.43 1997 190 52.48 38.51 8.48 82.51 1998 210 52.38 14.29 4.76 61.91 Beacon Hill Park 1996 135 58.46 39.07 19.63 77.90 1997 200 43.68 35.61 4.00 75.29 1998 210 51.43 12.38 0.95 62.86 Summit Park 1996 160 41.41 66.25 19.53 88.13 1997 210 47.46 48.62 10.79 85.29 1998 210 42.38 18.10 3.81 56.67 Playfair Park 1996 165 68.99 40.05 22.98 86.06 1997 210 52.24 39.75 14.80 77.20 1998 210 56.67 14.29 4.76 66.19 Mt.Tolmie 1996 165 83.79 40.66 11.06 83.39 1997 200 48.35 54.67 16.21 86.81 1998 210 51.91 21.43 5.71 67.62 Christmas Hill 1996 165 68.84 50.10 27.58 91.36 1997 210 55.26 40.82 11.84 84.24 1998 210 40.00 10.00 3.81 46.19 Layritz Park 1996 155 63.06 39.68 16.93 85.81 1997 210 49.50 35.22 7.61 77.11 1998 210 31.91 3.81 1.42 34.29 Overall Mean 1996 1645 58.28 41.66 16.23 80.71 1997 2030 46.80 36.49 8.23 75.06 1998 2100 43.00 11.29 3.00 51.29 55 A one-way analysis of variance (ANOVA) was used to examine differences in infestation by the filbert weevil, filbertworm, both insects, and total infestation by year. Infestation by the filbert weevil, filbertworm, both insects, and total infestation was significant by year (p<0.05) (Table 10). The mean number of infested acorns (total) was highest in 1996 and lowest in 1998 (Table 11). Filbert weevil infestation was highest in 1996 and did not change significantly from 1997 to 1998 while 1998 had significantly less filbertworm infested acorns than both 1996 and 1997 (Table 11). A univariate analysis of variance (UNIANOVA) was used to determine if there was a significant difference in infestation rates by the filbert weevil, filbertworm and both insects combined between sites, between sample dates (weeks) and the interaction of site X sample date. There was a significant (p<0.05) interaction between site and sample date for all cases in 1996,1997 and 1998 except two (filbertworm 1998, and both insects combined 1998) (Tables 12-14). Since there was this significant interaction, no conclusions can be drawn about the main effects. The significant interactions are illustrated in Figures 12-14. 56 Table 10. Results of one-way ANOVA: infestation of acorns by year for total infestation, filbert weevil, filbertworm, and both insects S o u r c e D F S u m of S a u a r e s M e a n S q u a r e F S i g . Tota l B e t w e e n G r o u p s Wi th in G r o u p s Tota l 2 7 3 7 7 3 9 116712 .75 4855550 .14 602262 .89 58356 .37 658 .82 88 .58 0 .000* Fi lbert weev i l B e t w e e n G r o u p s Wi th in G r o u p s Tota l 2 7 3 9 741 20627 .30 561871 .46 582498 .76 10313 .65 760.31 13.57 0 .000* F i lber tworm B e t w e e n G r o u p s Wi th in G r o u p s Tota l 2 7 3 9 741 124193 .39 553373.41 677566 .80 62096 .70 748.81 82 .93 0 .000* Both B e t w e e n G r o u p s Wi th in G r o u p s Tota l 2 7 3 9 741 22924 .46 200385 .90 223310 .37 11462 .23 271 .16 42 .27 0.000* 'Significant at p<0.05 57 Table 11. Mean total infestation, and infestation by the filbert weevil, filbertworm and both insects in 1996,1997 and 1998 Year Acorn Infestation category Total Filbert weevil Filbertworm Both 1996 80.71a1 58.28a 41.66a 16.23a 1997 75.06b 46.80b 36.49a 8.23b 1998 51.29c 43.00b 11.29b 3.00c 1 Means within acorn infestation categories followed by the same letter not significantly different. Bonferroni Test, (P<0.05) 58 T a b l e 12. R e s u l t s of U N I A N O V A : infestation of a c o r n s for site, s a m p l e date a n d the interaction of site x s a m p l e date for the filbert weev i l , f i lbertworm, both insects a n d total infestation in 1996 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . F i lbert weev i l M o d e l 149 354681 .20 2380.41 3.71 0.000* Date 14 198780.17 14198.58 2 2 . 1 5 0.000* S i te 9 31339 .68 3482 .19 5 .43 0 .000* Date x S i te 126 123302 .13 978 .59 1.53 0 .002* Error 2 8 2 180748.26 640 .95 Tota l 432 1311627 .67 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i a . F i lber tworm M o d e l 149 291357 .19 1955 .417 5 .314 0.000* Date 14 162316.60 11594.04 31.51 0 .000* S i t e 9 32977 .67 3 6 6 4 . 1 8 5 9 .958 0 .000* Date x S i te 126 88613 .64 703 .28 1.911 0.000* Error 2 8 2 103766 .79 367 .97 Tota l 432 582832 .778 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i q . Both M o d e l 149 76493.01 513 .38 2 .423 0.000* Date 14 2 1 8 3 0 . 9 4 1559 .35 7.37 0 .000* S i te 9 6993.31 777 .03 3 .67 0 .000* Date x S i te 126 47295.91 375 .36 1.774 0.000* Error 2 8 2 59671 .78 211 .60 Tota l 432 175108 .33 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i q . Tota l M o d e l 149 508534 .06 3412 .98 6 .230 0 .000* Date 14 377665 .56 26976.11 49 .24 0 .000* S i te 9 50577 .423 5619.71 4 .258 0.000* Date x S i te 126 74947 .75 594 .82 1.086 0.000* Error 282 154492 .79 547 .85 Tota l 432 1910565 .44 * s igni f icant at p<0.05 59 T a b l e 13. R e s u l t s of UNI A N O V A : infestation of a c o r n s for site, s a m p l e date a n d the interaction of site x s a m p l e date for the filbert weev i l , f i lbertworm, both insects a n d total infestation in 1997 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i d . Fi lbert weev i l M o d e l 149 306173 .78 2054 .86 6.371 0.000* Date 14 199249 .13 14232 .08 44 .13 0 .000* S i te 9 20196 .78 2 2 4 4 . 0 9 6 .99 0 .000* Date x S i te 126 84693 .88 672 .17 2 .08 0 .000* Error 2 9 3 94496 .36 322.51 Tota l 4 4 3 935126 .99 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . F i lbertworm M o d e l 149 2 0 6 2 4 4 . 1 4 1384.19 7.12 0 .000* Date 14 142910 .05 10207.86 52 .54 0.000* S i te 9 15541.10 1726.79 8 .88 0 .000* Date x S i te 126 46380 .96 368 .10 1.89 0.000* Error 2 9 3 56917 .00 194.26 Tota l 4 4 3 398890 .10 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . Both M o d e l 149 30309 .14 203 .417 2 .987 0 .000* Date 14 10163.20 725 .94 10.658 0 .000* S i te 9 2566 .92 285.21 4 .188 0 .000* Date x S i te 126 17110.47 135.78 1.994 0 .000* Error 2 9 3 19956.35 68.11 Tota l 4 4 3 57929 .79 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . Tota l M o d e l 149 534629 .63 3588 .118 11.51 0.000* Date 14 417941 .69 2 9 8 5 2 . 9 9 95 .77 0 .000* S i te 9 36395 .27 4043 .92 12.97 0 .000* Date x S i te 126 77888 .94 618 .17 1.98 0.000* Error 2 9 3 91337.471 311 .73 Tota l 4 4 3 1649986 .48 * s igni f icant at p<0.05 60 T a b l e 14. R e s u l t s of U N I A N O V A : infestation of a c o r n s for site, s a m p l e date a n d the interaction of site x s a m p l e date for the filbert weev i l , f i lbertworm, both insects a n d total infestation in 1998 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . Fi lbert weev i l 0 .000* M o d e l 149 287538 .00 1929.78 4 .99 Date 14 190928.00 13637.71 35 .27 0 .000* S i te 9 25213 .56 2801.51 7 .25 0 .000* Date x S i te 126 71396 .44 566 .63 1.47 0.004* Error 300 116000.00 386 .67 Tota l 450 792500 .00 S o u r c e D F S u m of M e a n S q u a r e F S i g . S q u a r e s F i lber tworm 0.000* M o d e l 149 3 8 1 2 6 . 4 4 255 .88 2 .82 Date 14 21429 .78 1530.70 16.84 0.000* S i te 9 3202 .00 355 .78 3.91 0 .000* Date x S i te 126 13494.67 107.10 1.18 0 .130 Error 300 27266 .67 90 .89 Tota l 450 78300 .00 S o u r c e D F S u m of M e a n S q u a r e F S i g . S q u a r e s Both 0 .000* M o d e l 149 4956 .44 33 .27 1.80 Date 14 2103.11 150.22 8 .15 0 .000* S i te 9 298 .67 33 .185 1.80 0 .068 Date x S i te 126 2554 .67 20 .28 1.10 0 .257 Error 300 5533 .33 18.44 Tota l 450 11400.00 S o u r c e D F S u m of M e a n S q u a r e F S i g . S q u a r e s Tota l M o d e l 149 362466 .67 2432 .66 5 .98 0.000* Date 14 241140 .00 17224.29 42.31 0.000* S i te 9 37097 .78 4121 .98 10.13 0 .000* Date x S i te 126 84228 .89 668 .48 1.64 0 .000* Error 300 122133 .33 407.11 Tota l 450 984600 .00 * s igni f icant at p<0.05 61 Figure 12. Significant interactions between the ten sample sites by date and infestation by the filbert weevil, filbertworm, both insects and total infestation in 1996 62 Figure 13. Significant interactions between the ten sample sites by date and infestation by the filbert weevil, filbertworm, both insects and total infestation in 1997 63 Figure 14. Significant interactions between the ten sample sites by date and infestation by the filbert weevil and total infestation in 1998 64 The percent of acorns in each damage category was determined from weekly-collected acorns (Table 15). In 1996, the year with the poorest acorn crop, the majority of the acorns were in damage category 6 (>97.5%) and in damage category 2 (>2.5% to 20%). The majority of acorns collected in 1997 were in damage category 6. While in 1998, the year with the largest acorn crop, most of the acorns were in category 0 (healthy) and 1 (trace damage) with the remainder of acorns spread over categories 2-6. 65 Table 15. Percent of acorns in the six damage categories in 1996,1997 and 1998 Damage Category Percent of acorns in each category Amount of Damage 1996 1997 1998 0 none 10.6 27.1 49.1 1 Trace to 2.5% 4.7 7.2 12.8 2 >2.5% to 20% 25.4 9.2 9.1 3 >20% to 50 10.7 6.0 6.6 4 >50% to 80 9.3 7.1 5.3 5 >80% to 97.5% 10.5 7.4 6.4 6 >97.5% 28.7 36.0 10.8 66 TRAP CATCHES Acorn Traps Acorn traps were not used in 1996. Acorns from the acorn traps were collected at the end of the collection season in 1997 and weekly in 1998. In the laboratory, these acorns were sorted into healthy and non-viable acorns. A total of 74 healthy and 264 non-viable (aborted) acorns were collected from the 72 traps in 1997 and 268 healthy and 280 non-viable in 1998. The mean number of acorns collected per trap per sample date over a 2 month period in 1998 ranged from a low of one acorn per trap for both healthy and non-viable acorns to a high of 3.4 per trap for non-viable acorns and 3.5 for healthy acorns (Table 16). More non-viable acorns were aborted early in the season (July 21st - September 1st) than late in the season and conversely, healthy acorns fell more often late in the season (September 4th to September 29th) (Figure 15). Weevil Traps The collection of filbert weevil adults in the field using emergence traps was not very successful. Only eight filbert weevil adults were collected from all 32 traps at the three sites over a 15-week collection period. Four adults were collected at Summit Park, one on May 4th and three on May 11th, one adult was collected at Rocky Point on May 12th 1998, and three at Christmas Hill, one each on May 4th, 12th and 19th. The main reason for the low number of adult weevils in the traps 67 Table 16. Mean number of healthy and non-viable acorns per trap, collected weekly from acorn traps at Mary Hill and Rocky Point in 1998 Mean number of acorns per trap Date non-viable healthy Mary Hill Rocky Point Mary Hill Rocky Point July 21 4.40 3.70 0.20 0.10 July 28 6.07 3.5 0.47 0.58 Aug. 4 5.31 4.27 1.38 0.33 Aug. 11 4.99 5.03 1.44 1.53 Aug. 18 7.20 3.89 1.60 1.33 Aug. 25 1.25 2.17 1.50 1.33 Sept. 1 2.21 2.25 1.51 1.67 Sept. 8 0.88 0.21 1.53 1.47 Sept. 15 0.50 0.04 1.25 1.52 Sept. 22 0.19 0.21 1.69 3.54 Sept. 29 0.20 0.21 4.50 3.21 68 Figure 15. Mean number of aborted and healthy acorns collected from acorn traps at Mary Hill and Rocky Point in 1998. 69 was due to the frequent vandalism of traps at Summit Park and Christmas Hill. Collection jars were stolen or broken on a regular basis, and many of the traps were crushed. At Mary Hill and Rocky Point, where vandalism did not occur, also only few adults were collected, which was probably due to the low weevil population. STRATA SAMPLING A 3X3 factorial experiment was used to determine the within tree distribution of filbert weevil and filbertworm infested acorns. The data was analyzed by a General Linear Model (GLM) since there was an unequal number of trees and locations in the analysis. 1997 Due to the poor acorn crop in 1997, only six trees could be located that met the criteria for strata sampling. Ninety acorns were collected from each of the six sample trees, 10 from each of the nine strata levels. Three trees were sampled from Rocky Point, two from Officers' Mess and one from Christmas Hill. The first interaction that was looked at was the level/direction interaction (Table 17). Since there was no significant interaction, the main effects were analyzed (Table 18). There was no significant difference (p<0.05) in the mean number of filbert weevil or filbertworm infested acorns at the three cardinal directions, or by the three strata levels (Table 19). 70 Table 17. Results of GLM: effects of insect infestation by level and direction for strata sampling in 1997 Effect F Error D F S i g . L e v e l 1.26 88 .00 0 .282 Direct ion 0.82 88 .00 0 .558 L e v e l x Direct ion 0.51 135.00 0 .908 * significant at p<0.05 71 Table 18. Results of GLM: infestation of acorns by the filbert weevil and filbertworm by level and direction for strata sampling in 1997 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . M o d e l 0 .454 Fi lbert weev i l 8 51 .33 6.42 0 .99 F i lbertworm 8 7.00 0 .875 0 .38 0 .936 Tota l 8 46 .82 5 .85 0 .63 0 .753 L e v e l 0 .102 Fi lbert weev i l 2 31 .00 15.50 2 .40 F i lbertworm 2 0.11 0 .06 0 .02 0 .976 Tota l 2 18 .93 9 .46 1.01 0 .372 Direct ion 0 .807 Fi lbert weev i l 2 2 .78 1.389 0.21 F i lber tworm 2 0 .78 0 .389 0.17 0 .845 Tota l 2 1.93 0 .963 0 .10 0 .903 L e v e l x Direct ion 0 .610 Fi lbert weev i l 4 17.56 4 .39 0 .68 F i lber tworm 4 6.11 1.53 0 .66 0 .622 Tota l 4 25 .96 6 .49 0 .69 0.601 Error Fi lbert weev i l 4 5 290 .67 6 .46 F i lber tworm 4 5 103 .83 2.31 Tota l 4 5 421 .50 9 .37 Tota l Fi lbert weev i l 54 1068.00 F i lber tworm 5 4 199.00 Tota l 54 1635.00 * Significant at p<0.05 72 Table 19. Mean acorn infestation by strata level in 1997 Strata Filbert weevil Filbertworm Total Level 1 4.50a1 1.22a 5.22a 2 2.67a 1.33a 3.83a 3 3.83a 1.28a 4.89a Direction 1 3.94a 1.33a 4.83a 2 3.67a 1.11a 4.72a 3 3.39a 1.39a 4.39a 1 Means within strata (level and direction) followed by the same letter are not significantly different. Bonferroni Test, P<0.05 73 1998 In 1998, acorns were collected by strata sampling from 24 trees. From 11 of the trees, acorns were sampled from the nine strata sections of the tree (3 levels x 3 directions). Thirteen of the trees, however, did not have acorns on all sides of the tree and for this reason only the three levels (lower, middle and upper) were sampled. The GLM analysis was first run on the 11 trees from which acorns were collected from all nine strata sections (Group 1). Results showed that there was no significant level x direction interaction and no significant difference in infestation by cardinal direction (Table 20). For this reason, data from all 24 trees were analyzed together (Group 2) to determine if there was a significant difference of infestation by level. Again, there was no significant interaction between level and direction (Table 20). With all 24 trees combined, there was a significant difference (p<0.05) in filbert weevil infestation by level (Table 21). There were significantly more filbert weevil infested acorns in the lower section of the tree than the middle- and upper-sections (Table 22). There was no significant difference in filbert weevil infestation between the middle and upper levels. As with the 1997 study, there was no significant difference in filbertworm infestation by tree level or cardinal direction. 74 Table 20. Results of GLM: effects of insect infestation by level and direction for strata sampling in 1998 Effect G r o u p F Error D F S i g . L e v e l 1 1.50 178.00 0 .182 2 2 .48 412 .00 0 .023* Direct ion 1 1.04 178.00 0 .398 2* L e v e l x Direct ion 1 0 .16 270 .00 0 .999 2 0 .45 621 .00 0 .943 * Significant at p<0.05 * A c o r n s in Group 2 were only collected by level 75 Table 21. Results of GLM: infestation of acorns by the filbert weevil and filbertworm by level and direction for strata sampling in 1998 S o u r c e D F S u m of S q u a r e s M e a n S q u a r e F S i g . M o d e l Fi lbert weev i l 8 106.62 13.33 1.85 0 .070 F i lber tworm 8 2 .58 0.32 1.06 0 .396 Tota l 8 106.84 13.34 1.80 0 .080 L e v e l o.oor Filbert weev i l 2 101 .93 50 .96 7.06 F i lbertworm 2 0 .25 0 .13 0.41 0 .665 Tota l 2 99 .79 49 .89 6.71 0.002* Direct ion 0 .803 Fi lbert weev i l 2 3 .15 1.59 0 .22 F i lbertworm 2 1.36 0 .68 2 .22 0.111 Tota l 2 5 .15 2 .57 0 .35 0 .708 L e v e l x Direct ion 0 .995 Fi lbert weev i l 4 1.52 0 .38 0 .05 F i lbertworm 4 0 .97 0 .24 0 .79 0 .530 Tota l 4 1.91 0 .48 0 .06 0 .992 Error Fi lbert weev i l 2 0 7 1494.42 7 .22 F i lber tworm 2 0 7 63 .38 0.31 Tota l 2 0 7 1539.75 7 .44 Tota l Fi lbert weev i l 216 4564 .00 F i lber tworm 2 1 6 81 .00 Tota l 216 4790 .00 * Significant at p<0.05 76 Table 22. Mean acorn infestation by strata level in 1998 Strata Filbert weevil Filbertworm Total Level 1 4.67a1 0.26a 4.76a 2 3.33b 0.31a 3.47b 3 3.11b 0.22a 3.21b Direction 1 3.62a 0.22a 3.75a 2 3.61a 0.19a 3.67a 3 3.88a 0.37a 4.03a 1 Means within strata (level and direction) followed by the same letter not significantly different. Bonferroni Test, P<0.05 77 FILBERT WEEVIL BIOLOGY The first indication of filbert weevil activity in all 3 years of weekly collections was the presence of oviposition punctures. In 1996, oviposition punctures were first observed on July 25 (Figure 16), and on July 8th and July 21st for 1997 (Figure 17) and 1998 (Figure 18), respectively. Eggs were found shortly after oviposition punctures on August 6,1996 but in 1997 and 1998, eggs were found on the same dates as oviposition punctures were first seen. Weevil larvae were first found on August 15th, August 12th and on August 11th in 1996,1997 and 1998, respectively. Emergence holes were first observed on September 9 (1996), September 2 (1997) and September 8 (1998). All observations for weekly collections were stopped at the end of September when all acorns had fallen to the ground. 78 2.51 C V J C7> C O C X I o> C O c-o o> C O o o Col lect ion Date Figure 16. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1996. 79 1.6 n Collection Date Figure 17. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1997. 80 1.2 Collection Date Figure 18. Mean number of oviposition punctures, eggs, larvae and emergence holes of the filbert weevil by sample dates in 1998. 81 Eggs The eggs are small, spiracle and semi-translucent white with a very fragile shell (Figure 19). Eggs are, on average, 0.73 mm long and 0.49 mm wide (Table 23). Filbert weevil eggs, reared in the laboratory on artificial diet, hatched on average in 10.5 days (range: 6 - 15 days). Larvae Filbert weevil larvae are robust, legless, "c" shaped, vermiform larvae. They are cream color with a dark-brown head capsule with large mandibles (Figure 20). Although the larvae have no legs, they are extremely mobile. The larva mines the acorn, with the early instar feeding mainly on the surface of the cotyledon, right underneath the pericarp (Figure 21), and only the late instars penetrate the center of the cotyledon. The last instar larvae emerge from the acorn when they are fully fed by chewing a circular emergence hole either while the acorn is on the tree, or after it has fallen to the ground. These mature larvae then burrow into the soil up to 15cm and overwinter as larvae. Head capsules were measured on a total of 682 filbert weevil larvae. In each year separately, as well with all 3 years combined the frequency distribution of head capsule widths indicate four distinct peaks, representing four larval instars (Figure 22). 82 Figure 19. Filbert weevil egg. Pericarp is cut away around the egg to expose it (10x). 83 Table 23. Mean length and width of filbert weevil eggs "Length Width n 105 105 Mean (mm) 0.73 0.49 Range (mm) 0.65 - 0.81 0.39 - 0.54 SE of mean 0.004 0.004 Variance 0.002 0.002 84 Figure 20. Filbert weevil larva (12x). 85 C. D. Figure 21. A) Early instar filbert weevil larva feeding (pericarp has been removed from acorn). B) Larva mining in lightly damaged acorn. C) Larva in moderately damaged acorn. D) Severely damaged acorn (2x). Note: Both acorns B and C are beginning to germinate. 86 Figure 22. Histogram of head capsule measurements of the filbert weevil in 1996,1997,1998 and all three years combined. 87 The mean width of filbert weevil head capsules for the four instars was 0.23 mm, 0.52 mm, 0.93 mm and 1.45 mm, respectively (Table 24). The range of the head capsule for the four larval instars is given in Table 24. 88 Table 24. Head capsule widths for the four larval instars of filbert weevil (1996, 1997 and 1998 data combined) Instar .j st 2 n d 3^ 4 t f l n 37 99 170 376 Mean (mm) 0.23 0.51 0.93 1.45 Range (mm) 0.15-0.32 0.33-0.67 0.70-1.11 1.12-1.8 SEMean 0.006 0.009 0.007 0.006 Variance 0.001 0.008 0.008 0.01 89 The mean duration of successive larval instars, as estimated from the laboratory reared (25°C) and over wintered larvae was: egg to 1st instar 10.5 days, 1st to 2n d instar 9.0 days, 2nd to 3rd instar 9.3 days and 3rd to 4th instar 9.3 days (Table 25). Although the 4th instar larvae fed on diet for up to 12 days, this stage spends from 8 to 12 months in the soil, without feeding, prior to pupation. Pupae Upon completion of feeding in the 4th instar, the larvae emerge from the acorn by chewing a circular emergence hole through the shell of the acorn (Figure 23) either while the acorn is still on the tree or after it has fallen to the ground. The larva then burrows 15 cm or more into the soil, and form a chamber in the soil in which they overwinter. After forming the cell, the larvae remain quiescent for several months, and pupate in the spring. Larvae placed in the laboratory glass observation vials in February 1998 began to pupate on August 21,1998. The pupal stage in the laboratory ranged from 7 to 23 days and averaged 12 days. The pupae are exarate and look much like a pale, mummified adult. The eyes darken a few days after pupation and then the mandibles and proboscis darken. On the ventral side of the pupa (Figure 24) the legs, proboscis and antennae can be readily seen and on the dorsal side the elytra are visible. 90 Table 25. Duration of the four larval instars of the filbert weevil reared on artificial diet in the laboratory at 25°C in 1998 Instar Egg to 1st 1st to 2na 2nd to 3rd 3rd to 4th n 50 9 10 16 Mean (days) 10.46 9.00 9.30 9.31 Range (days) 6-15 5-11 4-13 6-12 SE of Mean 0.44 0.60 0.92 0.46 Variance 9.89 3.25 8.46 3.43 91 Figure 23. Filbert weevil emergence hole (3x). 92 Figure 24. Dorsal and ventral view of a filbert weevil pupa (5x). 93 Adult The teneral adult is light tan with dark claws and mandibles. It took an average of 10.25 days for teneral adults to harden and gain full coloring. Hardened adults are brownish-beige with darker spots on the elytra. They eyes are black and the legs and antennae are similar in color to the body. Females are significantly (p<0.05) larger than males in all categories (length, width and rostrum length) (Table 26) (Figure 25). The male is densely covered with long hairs on the pygidium with these hairs extending beyond the elytra. Females have little or no hair. A total of 594 adults were collected from beating, laboratory rearings and emergence traps. The male: female ratio was 308:286 (Table 27). The hypothesis of a 1:1 male to female ratio was tested by a Chi-square analysis. It was found that a 1:1 ratio was supported (%2= 0.815, df=1). Females reared in the laboratory lived longer on average than laboratory reared males but this difference was not significant (p<0.05) (Table 28). Using an independent samples t-test, it was shown that there is a significant difference in the longevity of adults if they were supplied with food or starved, with starved weevils living significantly longer. 94 Table 26. Body size of female and male filbert weevil adults Body Size Female* Male* Length (mm) n 92 73 Mean 6.61 5.85 range 5.50-7.54 4.69-6.58 SE of mean 0.04 0.05 Width (mm) n 92 73 Mean 3.45 3.05 range 2.75-3.98 2.48-3.54 SE of mean 0.03 0.03 Rostrum length (mm) n 92 73 Mean 3.82 2.51 range 2.77-4.42 3.15-3.44 SE of mean 0.05 0.05 * all means significantly different, t-test p<0.05 95 Figure 25. Male (left) and female (right) filbert weevil adults (6.5x) 96 Table 27. Number of filbert weevil adults collected by various methods in 1998 Number of filbert weevil adults collect by Rearing Beating Emergence Total Traps Female 256 24 6 286~ Male 283 23 2 308 Total 539 47 8 594 97 Table 28. Longevity of males and females reared in the laboratory both with and without food With food Without food Female Male Female Male n 210 252 11 13 Mean (days) 28.19a1 26.79a 42.00b 32.62c Range (days) 4-95 3-76 14-70 11 -115 SE of Mean 1.23 0.93 4.65 7.69 Variance 317.51 217.97 230.0 768.92 1 Means followed by the same letter not significantly different, t-test, p<0.05 98 Adults (both males and females) emerging late in the season (October / November) lived significantly (p<0.05) longer than adults emerging in August and September (Table 29). Female filbert weevils oviposit into the acorn by drilling a hole into the acorn pericarp with the rostrum. She then excavates one or several galleries under the shell of the acorn with strong mandibles attached to the end of the rostrum. The female then turns around and lays from one to six eggs into the gallery. The eggs are usually laid under the pericarp, at the edge of the acorn cap. The process of gallery excavation and egg laying in the acorn often causes a black discoloration around the oviposition hole (Figure 26) Filbert weevil oviposition studies were not as successful as was hoped. Filbert weevil females only oviposited into fresh, green acorns, which were only available until the end of September. Adults however emerged from the buckets set up in 1997 until November 1998 (Table 30). All attempts to induce the females to lay eggs on mature (brown) acorns or artificial diet were unsuccessful. Twenty-eight female weevils laid eggs in acorns (Table 31). The mean number of eggs laid per adult was 2.3 (range 0-6). Oviposition occurred on average 8.2 days after of emergence (range 1 to 30 days) (Table 32). No eggs were laid after September 21. 99 Table 29. Longevity of male and female filbert weevil adults emerging in August, September and October/November Time of Emergence n Mean (days) SE of mean Females August 58 11.74a1 0.64 September 62 27.37b 1.94 October/November 90 39.36c 1.72 Males August 51 9.12a 0.75 September 65 24.63b 1.44 October/November 134 37.70c 1.03 1 Means followed by the same letter within gender not significantly different. Bonferroni Test, p<0.05 100 Figure 26. Acorn damage caused by filbert weevil oviposition (10x). 101 Table 30. Number of filbert weevil adults emerged from laboratory reared larvae from August 5th to November 2nd 1998. Number emerged Date Male Female August 5 17 14 August 6 1 5 August 7 0 6 August 8 0 1 August 10 3 2 August 12 4 4 August 24 4 4 August 26 1 0 August 28 0 4 August 31 1 1 September 2 1 0 September 4 0 6 Septembers 10 3 September 9 5 5 September 11 12 7 Septembers 23 22 September 16 9 11 September 18 3 5 September 21 16 13 October 2 28 19 October 5 13 10 October 19 14 15 October 21 43 38 October 28 34 17 October 30 13 16 November 2 28 28 Total 283 256 102 T a b l e 3 1 . Date of e m e r g e n c e , oviposit ion a n d the number of e g g s la id by filbert weev i l adul ts 1998 Adul t Date of No . of e g g s per number E m e r g e n c e Ov ipos i t ion ov iposi t ion puncture 1 Augus t 5 Augus t 10 1 1 A u g u s t 5 Augus t 10 1 2 Augus t 5 August 10 2 2 Augus t 5 Augus t 10 1 3 Augus t 10 August 19 4 4 Augus t 10 Augus t 22 4 5 A u g u s t 5 Augus t 12 2 6 Augus t 5 Augus t 10 2 7 Augus t 5 Augus t 12 1 7 Augus t 5 August 14 3 8 Augus t 6 Augus t 12 2 8 A u g u s t 6 Augus t 12 2 8 Augus t 6 August 19 2 9 Augus t 5 Augus t 19 3 9 A u g u s t 5 Augus t 19 3 10 Augus t 5 August 10 1 10 Augus t 5 Augus t 10 1 11 A u g u s t 5 Augus t 10 1 11 Augus t 5 Augus t 10 1 11 Augus t 5 Augus t 12 1 11 Augus t 5 Augus t 12 2 11 Augus t 5 Augus t 12 2 12 A u g u s t 5 Augus t 10 1 12 Augus t 5 Augus t 12 1 13 Augus t 6 Augus t 17 2 14 Augus t 5 August 2 4 1 15 Augus t 5 Augus t 19 1 16 A u g u s t 13 August 2 4 1 17 Augus t 18 Augus t 21 1 18 Augus t 7 S e p t e m b e r 8 1 19 Augus t 31 S e p t e m b e r 8 2 20 S e p t e m b e r 9 S e p t e m b e r 2 3 1 21 S e p t e m b e r 8 S e p t e m b e r 18 2 2 2 S e p t e m b e r 8 S e p t e m b e r 8 2 22 S e p t e m b e r 8 S e p t e m b e r 8 1 2 3 S e p t e m b e r 14 S e p t e m b e r 21 1 2 3 S e p t e m b e r 14 S e p t e m b e r 21 1 2 4 S e p t e m b e r 11 S e p t e m b e r 21 1 2 5 S e p t e m b e r 14 S e p t e m b e r 21 1 2 6 S e p t e m b e r 14 S e p t e m b e r 18 1 2 7 S e p t e m b e r 14 S e p t e m b e r 21 1 2 8 S e p t e m b e r 14 S e p t e m b e r 18 1 103 Table 32. Time elapsed from adult emergence to oviposition Days to oviposition n 41 Mean (days) 8.22 range (days) 1-30 SE of Mean 0.79 variance 25.78 104 FILBERTWORM BIOLOGY The filbertworm was less common and caused less damage than the filbert weevil in Garry oak acorns collected in the Greater Victoria area in all 3 years of the study. Because the filbertworm is less important than the filbert weevil, in terms of damage done to acorns, as well as time constraints, less time was spent on the filbertworm, and filbertworm larvae were not reared. Consequently, the data and observations obtained on the biology of the filbertworm are incomplete. Egg Eggs of the filbertworm were rarely seen on the acorns collected during this study. On the 13,399 acorns collected and examined, from weekly and strata sampling, only three eggs were found. The eggs are waxy-white and transparent and are extremely fragile (Figure 27). Eggs are laid singly on the acorns, as was found in this study, or on branches (Brown and Eads 1965). Larvae After the eggs hatch, the larvae burrow into the acorn through the microphile. Filbertworm larvae, in the field, were first found in dissected acorns on July 29th in 1996 (Figure 28), July 8th in 1997 (Figure 29) and August 11th in 1998 (Figure 30). Larvae of the filbertworm are creamy white with a golden head and thoracic shield (Figure 31) and may be up to 15 mm long in the last instar. 105 Figure 27. Filbertworm egg (8x). 106 •61 C \ J CX> C O CNI cx> C D C O cr> C D C O CNI CNI <G 1 — ^— CNI ^ j , : CNI >^  >--=> CJ> <c D l <c CD C O O . CD C O "5. CD C O O -CD C O Collection Date Figure 28. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1996. 107 .5 Collection Date Figure 29. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1997. 108 .16 Collection Date Figure 30. Mean number of filbertworm larvae and emergence holes per acorn in weekly-collected acorns in 1998. 109 Figure 31. Last instar filbertworm larva (5x). 110 The larvae have true legs and crochets on the abdominal prolegs (Brown and Eads 1965) and are highly mobile. Last instar larvae were first observed to have chewed emergence holes (Figure 32) in acorns on August 26, in 1996, August 19, in 1997, and August 25, in 1998. In all 3 years, emergence holes were found in the weekly-collected acorns until the end of September. The emergence holes of the filbert worm were observed to be oval in shape, and a maximum of four was found in one acorn. Filbertworm larvae do extensive damage to acorns, often hollowing out the entire acorn and leaving a mass of frass and webbing (Figure 33). Larvae bore their way out of the acorn to seek a place for hibernation. The last instar larvae overwinter in tough cocoons within the top few centimeters of the soil. Filbertworm head capsule widths were measured in 1996,1997 and 1998. Unfortunately, the number of filbertworm head capsules measured was low in all 3 years of the study (236, 190 and 54 in 1996, 1997 and 1998, respectively). Due to this low number of specimens, a meaningful trend could not be established separately in the 3 years, therefore, the data obtained in 1996,1997 and 1998 were combined into one histogram. 111 re 32. Filbertworm emergence hole (3x). 112 Figure 33. Severe feeding damage caused by the filbertworm. Frass and webbing fill the acorn (2.5x). 113 Even with the combined data from all 3 years, the low number of measurements makes it difficult to determine with certainty the number of peaks corresponding to the larval instars in the histogram (Figure 34). In the histogram, four peaks are obvious, but with more measurements, however, there may be additional peaks. Pupae After the filbertworm larva exits the acorn, it burrows into the duff in the upper 10-15 centimeters of the ground, and remains there as a larva within the cocoon until the following spring (Figure 35). In the spring, the larva turns into a red-brown pupa and emerges 10-15 days later (AliNiazee 1981). Adult The adult filbertworm moths emerge in July or early August, as estimated from the appearance of larvae. The adult is approximately 10mm long at rest with winds folded, and has a wingspan of approximately 18 mm, which is within the 11 to 20 mm range reported by Brown and Eads (1965). They are reddish-brown with a coppery band across the middle of the wing, and a narrower band toward the outer wing margin (Figure 36). The insect has one generation per year, although a few undergo a partial generation and may pupate and emerge as adults in the same year (AliNiazee 1980). 114 40 Head capsule width (mm) Figure 34. Histogram of head capsule measurements of the filbertworm combined from 1996,1997 and 1998. 115 Figure 35. Filbertworm larva overwintering in cocoon (top) (3.5x) and filbertworm pupa (bottom) (7x). 116 ure 36. Filbertworm adult (5.5x). 117 GERMINATION TESTS 1997 In 1997 a sub-sample of 1,500 acorns were randomly selected from a mass collected sample of 5,000 acorns. Each acorn in the sub-sample was processed by measuring its length, width and weight, and then were cut open to identify the insect causing the damage and to assess the amount of feeding. Each acorn was classified into one of four damage categories: healthy (no damage to the kernel); light damage (trace to 20% damage to the kernel); moderate damage (21% to 50% damage to the kernel); and severe damage (>50% damage to the kernel). The measurements of length and weight of each acorn were plotted grouping the four damage categories. Analysis of covariance was used to determine if the four lines differed significantly in both slope, and level. It was found that there was no significant difference between the slope and level of the light and moderate damage categories and, therefore, these two categories were combined to form the new light/moderate damage category. 118 A linear regression equation was developed from the data using length and weight as the independent variables, and damage class as the dependent variable. Y= a + biXi + b2x2 where: Y= damage rating a= 1.97 bi= -0.47 b2= -0.67 xi= weight x2= length Both weight and length were significant (p<0.05) in the equation (Table 33). The equation was also significant (p<0.05) with an Rsq of 0.46 (Table 34). Although linear regression was used for this analysis, a better choice would have been logistic regression since the dependent variable is categorical. 119 Table 33. Significance of the variables weight and length in the regression equation for estimating damage in 1997 Variable Partial F Sig. F Weight 428.96 0.000* Length 607.91 0.000* * Significant at p<0.05 120 Table 34. Regression equation for estimating damage in 1997 Source DF Sum of Mean F Sig.F Squares Square (regression) Regression 2 663.12 331.56 902.99 0.000* Residual 2159 792.74 0.37 significant at p<0.05 RSq=0.46 121 A second sub-sample of acorns was selected randomly from the remaining group of mass collect acorns (from which the equation to estimate damage was determined). The length and width of the acorns were measured and applied to the regression equation to estimate the damage class of the acorn without dissecting it. Acorns were measured until there were 150 acorns in each of the three damage classes. Ninety acorns were randomly chosen from each of the three classes and were planted on November 1,1997 in styroplugs and kept in the greenhouse at PFC. The first acorns germinated on February 16th 1998 and were from the healthy category. A total of 19 acorns germinated from the healthy category and 12 from the light/moderate damage category. No acorns germinated from the severe damage category (Table 35). There was no difference in the mean height of seedlings grown from healthy, or from light/moderately damaged acorns (Figure 37). 122 Table 35. Proportion of the acorns germinating in the three damage classes 1997 Damage Number of Acorns % Class* Planted Germinated Germinated Healthy 90 19a1 21.1 Light/moderate 90 12a 13.3 Severe 90 Ob 0 * Damage Class Healthy: no damage to the kernel Light/moderate damage: trace to 50% damage to the kernel Severe damage: >50% damage to the kernel 1 Means followed by the same letter not significantly different, t-test p<0.05. 123 5 Date Figure 37. Height growth of Garry oak seedlings grown from healthy and light/moderately damaged acorns planted on November 1st, 1997. 124 1998 Acorns for the 1998 germination tests were sampled and processed in the same way as for the 1997 samples. Again there was no significant difference between the light and moderate damage categories, and these two categories were combined as in 1997. In 1998, it was found that the best correlation of independent variables to damage (dependent variable) was a crude formula for the inverse density of an acorn: (width) 2(length)/weight. This formula gave a correlation coefficient of 0.80 vs. 0.28 for length alone. A quadratic regression equation was developed from the data using density as the independent variables, and damage class as the dependent variable. Y = a+biX+b2X2 where: Y= damage rating a= 0.86 bi= 0.042 b2= -0.006 x= (width)2(length)/weight The equation was significant (p<0.05) (Table 36) with an Rsq of 0.80. 125 Table 36. Regression equation for estimating damage in 1998 Source DF Sum of Mean F Sig. F Squares Square (regression) Regression 1 260.81 260.81 1659.91 0.000* Residual 592 93.01 0.16 significant at p<0.05 RSq=0.80 126 The length and weight of a second sample of acorns (from the same sample that the equation was derived from) was used in the regression equation to estimate acorn damage without dissecting the acorn. Approximately 200 acorns for each damage class were measured and 100 of these acorns were randomly chosen from each of the three damage classes to be tested for germination using the method described by Bonner (1984). Bonner's method for seed testing was used in the second year because of time constraints. After 28 days, 42% of the healthy acorns germinated, 23% of the light/moderately damaged acorns germinated, and 0% of the severely damaged acorns germinated (Table 37). 127 Table 37. Proportion of acorns germinating in the three damage classes in 1998 Damage Number of Acorns % Class* Set up Germinated Germinated Healthy TfJO 42a1 42 Light/moderate 100 23b 23 Severe 100 0c 0 * Damage Class Healthy: no damage to the kernel Light/moderate damage: trace to 50% damage to the kernel Severe damage: >50% damage to the kernel 1 Means followed by the same letter not significantly different, t-test p<0.05. 128 DISCUSSION ACORN PRODUCTION AND INFESTATION The cyclic nature of Garry oak acorn production, with the variation in good and poor crop years (poor crops in 1996 and 1997; good crop in 1998) serves as a form of natural control for the filbertworm, and to a lesser extent, the filbert weevil. There is an inverse trend between Garry oak acorn crop size and acorn infestation, (high infestation in poor crop years and low infestation in mast years) and has been shown by others to be a critical factor limiting pecan weevil (Curculio caryae) populations (Gibson 1964, Myers 1978). There are, however, conflicting reports on the relationship between acorn crop size and insect infestations. Several researchers have also reported a similar inverse trend between acorn production and infestation rates for the filbertworm, and the pecan weevil (Sidney 1948, Beal 1952, Gibson 1972, Beck 1977, McQuilkin and Musbach 1977, Borowicz and Juliano 1986). Others, however, have found no such correlation (Gibson 1971, Kearby et al. 1986). For filbert weevil infestation rate to fluctuate only moderately from high to low crop years, the filbert weevil must infest more acorns in mast crop years than in low crop years. This hypothesis was supported both by the number of oviposition punctures per infested acorn, as well as by the number of infested acorns each year. In low crop years (1996 and 1997) the density of filbert weevil oviposition punctures per infested acorn was higher (2.44 and 1.79 in 1996 and 129 1997, respectively) than in the mast crop year (1.68 in 1998) (Tables 5-7). The poor searching ability of filbert weevil adults (Kearby et al. 1986) may prompt adults to oviposit more frequently on a single acorn when the crop is not abundant. In 1998, the number of healthy acorns collected in acorn traps was almost four times that of low crop years, however, the number of infested acorns collected, remained almost the same (1,126,1,345 and 1,322 infested acorns in 1996,1997 and 1998, respectively) indicating the weevils infest more acorns in high crop years. The inverse relationship between crop size and filbertworm attack may be the result of filbertworm searching ability. It is hypothesized that filbertworm adults may be efficient searchers in low acorn years, but may be unable to respond to, and exploit a large increase in acorn crop size, resulting in a reduced infestation in mast crop years. PROPORTION OF INFESTED ACORNS BY YEAR, SITE AND SAMPLE DATE Infestation of acorns by the filbert weevil and filbertworm were shown to vary significantly (P<0.05) by year, with the filbert weevil attacking more acorns than the filbertworm in each of the 3 years (Table 9). These findings agree with those of Brezner (1960) and Jones (1959), both of whom reported a variation among the proportion of Curculio and Cydia attacked acorns among years. 130 The variation in acorn infestation among the 3 years can be attributed to the variation in crop size among the 3 years, the size of the insect population, and the resulting interaction of the insect population with the acorn crop (Myers 1978). Over-wintering survival, insect searching ability, predation of acorns and larval survival inside the acorns, and competition with other species of insects may effect the insect/crop interaction, and therefore, the year to year variation in infestation and damage. Although there was a significant site x date interaction and, therefore, the main effects could not be analyzed, overall infestation rates at the 10 sites ranged considerably (from a low of 48.24% to a high of 91.39% in 1996, 51.43% to 86.81% in 1997 and 24.29% to 67.62% in 1998). These differences may have been caused by variation of the environment at the study sites that may contribute to differences in filbert weevil and filbertworm survival. Soil temperature and moisture are two variables known to affect overwintering survival in other curculionids, such as boll weevils (Anthonomus grandis B.) (Price et al. 1985, Henneberry et al. 1990, Stone et al. 1990, Slosser and Fuchs 1991). Microclimates at some of the sites, caused by asphalt parking lots and reduced vegetation, could have resulted in higher temperatures, which have been shown to affect insect survival and development (Wellington 1950). At some of the highly used sites, the high traffic by humans may have lead to compaction of the soil, which prevents or reduces the ability of larvae to burrow 131 into the soil to overwinter, thereby causing larval mortality. If the larvae are successful in burrowing into these compacted soils, emergence of adults may be impeded as the adults may not be able to burrow though the compacted layer of the soil to emerge (Harris and Ring 1980, Alverson et al. 1984). This would lead to a decreased adult population, and, therefore, decreased infestation levels. Similarly, the 'natural' areas with loose, undisturbed soils would allow both larvae and adults unimpeded movement and emergence from the soil, thus resulting in increased adult populations and infestation levels (Gibson 1964). The time, location, and method of acorn collection all influence the accuracy of the determination of acorn infestation. Acorns collected from the ground, may have higher rates of infestation than those collected from the tree since insect infested acorns tend to drop in early September, before sound acorns, but after aborted acorns which fall in July and August (Griffin 1971, Boucher and Sork 1979, Schettler and Smith 1980, Menke and Fry 1980, Stephenson 1981, Stein 1990, Swiecki et al. 1991). If all acorns are collected off the ground, before healthy acorns drop, sampling of the acorns from the ground may result in an overestimation of infestation levels. Since the method of collection, time and location will significantly affect the estimate of overall damage levels due to insects, care must be taken when assessing infestation rates. In order to obtain the most accurate infestation levels, acorns should be collected from the ground, after all healthy acorns have also dropped. 132 SEED TRAPS Patterns of abscission in this study were similar to those of other studies (Williamson 1966, Boucher and Sork 1979, Stephenson 1981, Feret et al. 1982 and others). Non-viable acorns fell in July and August, and made up the majority of acorns overall (Table 12). Healthy acorns, however, were the most common type falling in September with the majority of non-viable acorns falling before September 1st. The response by the tree to drop non-viable acorns may be advantageous. Dropping of undeveloped acorns may save energy, which can then be diverted to the remaining developing acorns left on the tree (Boucher and Sork 1979, Stephenson 1981), as well as act as a natural, thinning process. ACORN VIABILITY The most important factor in reducing the number of viable Garry oak acorns is the consumption of the cotyledon by filbert weevil and filbertworm larvae. Although feeding by these larvae contribute to decreased acorn viability, it was found that not only acorns in the healthy category (category 0: no damage), but, some acorns (up to 23%) in the light/moderate damage category (category 1-3: trace to 50% damage) germinated (Table 24 and 25). Others, (Matsuda 1982, Oliver and Chapin 1984, Ellison and Thompson 1987, Weckerly et al. 1989b, Andersson 1992, Swiecki et al. 1991) also found that a portion of the damaged acorns have the ability to germinate. Seedlings resulting from the acorns with depleted cotyledon however, may be more susceptible to desiccation, 133 environmental stress, and have lower survivorship to sapling age than seedlings originating from sound acorns (Barrett 1931, Barnett 1977, Stein 1990). Weckerly et al. (1989) suggested that germination of damaged acorns has little effect on the overall recruitment of new trees in the population (in their study, only 8% of damaged acorns germinated), but my data suggests otherwise. Acorns in the light/moderate damage category made up 40.8%, 22.4% and 28.5% (Table 10) of acorns overall in 1996,1997 and 1998, respectively. Although the seedlings from these acorns may not be as vigorous as those from undamaged acorns, they represent a large portion of potentially viable acorns, especially in low crop years. Acorns damaged by C. occidentis can still germinate due to a combination of acorn structure, as well as the chemical composition of the acorn. Filbert weevil adults were found to oviposit in the middle and proximal portion of the acorn (76.80% and 19.91%, respectively) and rarely in the distal end (3.29%) which is consistent with observations by Steele et al. (1993) with Curculio caryae (Horn) adults. Oviposition into the middle section of the acorn is regulated by the structure of the acorn, with the cap covering most of the proximal portion of the pericarp. The cap of the acorn is rough and provides a secure hold for the female to grasp onto while she oviposits around the edge of the cap, into the middle portion. Larvae were rarely found in the distal portion of the acorn (6.37%), indicating that larvae feed most often in the middle and proximal end of 134 the acorn. The movement of the larvae inside the acorns may be influenced by the high tannin content of acorns, which has been reported to act as a feeding repellent and can cause direct toxic effects to the larvae by reducing the digestibility, protein availability, or palatability of the acorn (Goldstein and Swain 1963 & 1965, Bennett 1965, Bate-Smith 1973, Chapman 1974, Freeland and Janzen 1974, Feeny 1968, 1969,1970 & 1976, Levin 1976, Bernays 1981, Martin and Martin 1982, Smallwood and Peters 1986, Robbins et al. 1987a & b, Weckerly et al. 1989b, Fleck 1990, Steele et al. 1993). The elevated tannin content in the distal portion of the acorn (Steele et al. 1993) (the portion containing the embryo) may act as a feeding deterrent in the distal end, thereby prompting the insects to feed in the middle and proximal portions of the acorn, protecting the seed embryo and increasing germination success. Healthy Garry oak acorns generally have up to 80% germination success (Stein 1990, Hagel pers. com. 1999). Healthy acorns in this study, however, had only low germination success (21.1% and 42% in 1997 and 1998, respectively). Since acorns grown for the 1997 germination test were planted in the same medium, and grown under the same environmental conditions (temperature, humidity and watering) as those that were grown in the greenhouse at PFC, the only explanation for the discrepancy in germination rates is the storage method and/or the length of the storage time in my study. Garry oak acorns require a moisture content of 30% or more in order to maintain viability (Jones 1959, Burns and Honkala 1990). It is unlikely that the moisture content was lower than 30% 135 since there was condensation in the plastic bags the acorns were stored in, but rotting of the emerging radical, due to the moisture, may have resulted in decreased germination (Jones 1959). Jones (1959) also showed that freezing is detrimental to acorn germination and just 1 hour at -9.5°C will kill the majority or acorns, and -6°C will kill 50% of acorns in 4 hours. However, the acorns in my study were stored at 4°C, thus, the effects of storage temperature were likely to be minimal. STRATA SAMPLING Acorns infested by the filbertworm were distributed homogeneously in both the three levels and the three cardinal directions of Garry oak trees in 1997 and 1998. Filbert weevil infested acorns, on the other hand, were found most often in the lower section of trees in 1998. In both 1997 and 1998, filbert weevil and filbertworm infestation did not differ by cardinal direction. The homogeneous distribution of infested filbertworm acorns in the crown could be attributed to the fact that filbertworm adults are good fliers and can readily reach the upper-, as well as the middle- and lower-sections of the crown (AliNiazee 1981, Peacock et al. 1988). Filbert weevil adults on the other hand, are slow, clumsy fliers (Brooks 1910), and more often exploit the lower-section (Lewis 1992, Eikenbary and Raney 1973). Filbert weevil adults also walk up the bole and branches of a tree, instead of flying, to reach the acorns in the canopy 136 (Brooks 1910, Kearby et al. 1986), therefore making access to the upper branches an arduous task. Differences in infestation rates of acorns within the tree canopy may also be due, in part, to uneven acorn distribution in the crown. Lewis (1992) reported that Quercus agrifolia in Marin County, CA, USA, had three times more acorns in the lower- and middle-sections of the tree than the top section. In contrast, a similar study in Berkeley, about 100km away, showed Q. agrifolia had the most acorns in the top section (Lewis 1989). However, Lewis (1992) attributed these differences in acorn abundance in the crown levels to the pruning and watering practices at the Berkeley site. Since acorn abundance in the crown levels of Garry oak trees was not examined in this study, it is not known if acorn abundance and distribution within the crown had any effects on the within tree distribution of filbert weevil or filbertworm infested acorns. FILBERT WEEVIL Although the rearing and oviposition tests conducted in the laboratory on the filbert weevil were not entirely representative of the natural environmental conditions, the information obtained from these laboratory observations, in combination with observations and data from the weekly collected acorns in the field, allow inferences to be made on the behavior and biology of the filbert weevil. 137 Filbert weevil adults began to emerge in the field in the first week of July, indicated by the presence of oviposition punctures on the acorns. Since in the laboratory, oviposition occurred, as early as, the first day of emergence (Table 23), the presence of oviposition punctures was used as an indicator of adult emergence in the field. In both field and laboratory rearing the emergence of the adults occurred over a 3-month period. However, the emergence of the adults in the laboratory was delayed by 2 months. Others (Dutcher and Payne 1986) have also found emergence of Curculio adults to span up to 3 months. The 2 month delay of filbert weevil adult emergence in the laboratory may be attributed to the medium used to overwinter the larvae (sand), although the sand was chosen based on a previous study (Gibson 1964) which resulted in superior emergence rates of pecan weevil adults from this medium. Soil moisture content in the buckets used to over-winter the larvae may also have contributed to the delayed emergence. Reduced soil moisture has been shown to increase the penetration resistance of the soil, thereby possibly contributing to the delay of adult emergence (Dupree and Bissell 1965, Harris and Ring 1980, Alverson et al. 1984, Schraer et al. 1998). Although all attempts were made to keep the sand uniformly moist, there was a concern that over-watering the soil may result in anoxic soil conditions or drowning of the larvae (Ricca et al. 1996). It is possible, therefore, that the sand in the buckets was not moist enough, and this 'artificial drought' may have caused the delayed emergence of the adults, as Harris and Ring (1980) reported for the pecan weevil. Reduced temperature has also been 138 shown to delay emergence of the pecan weevil adult (Curculio caryae) by up to 3 months (Kearby et al. 1986). However, in this study, temperature is not thought to be a factor affecting adult weevil emergence since the larvae were over-wintered outside, at ambient temperatures. There was no way to ascertain from field-collected acorns the total number of eggs that one female deposited. In my laboratory studies, the maximum number of eggs deposited by one female weevil was six, which is considerably less than what Criswell et al. (1975) found in Curculio caryae where one female could lay up to 96 eggs. Since oviposition is most likely influenced, and closely related to acorn phenology, the disparity between the number of eggs laid by C. caryae and C. occidentis may be due to unsuitable host acorn conditions in the laboratory (acorns may have been too mature for oviposition), unsuitable mating chamber, or simply a difference in the egg laying capacity of C. caryae and C. occidentis. Laboratory reared larvae were shown to complete four successive instars, which is consistent with studies of larval stages of other Curculio species (Sidney 1948, Gibson 1969, Harp and VanCleave 1976a,b & c). Development times for the instars of laboratory reared Curculio occidentis are longer than those reported for Curculio caryae (Sidney 1948, Harp and Van Cleave 1976a). The length of each larval instar may have been influenced by many factors, the most important being that the larvae were reared on artificial diet, and not on acorns. In addition, disturbing the larvae to measure head capsule size, and the constant 139 temperature maintained in the growth chamber are unnatural conditions, which may have effected the length of each instar. Unfortunately, it was not possible to determine the duration of individual instars from the larvae collected in the field because of the cryptic location of the larvae in the acorn. The adult females live about 1 day longer than males (although the difference was not significant) with females living approximately 28.1 days and males 26.8 days. This is considerably longer than the 2-week life span reported by Brezner (1960) for the pecan weevil. Harris and Ring (1980) also found that males lived longer than females. The availability of food did not influence longevity of adults in this study, as the duration of the adult life stage was longer for starved specimens than for fed insects. Similarly, Brezner (1960) found no difference in the longevity of Curculio caryae adults regardless whether they were supplied with food or not. Feeding, therefore, is not absolutely essential to the long term survival of filbert weevil adults. Crisswell et al. (1975) found that pecan weevils that emerged early in the season (July 21- Aug.8) had a longer life span than those that emerged in the middle (Aug 12-26) and late (September 1-17) portion of the emergence period. They reported that weevils that emerged in the middle of the emergence period had a longer average life span than those that emerged in the late part of this period. This is in direct contradiction to what was found for the filbert weevil. Adults that emerged late in the season (October/November) lived significantly longer than 140 those that emerged in the middle portion (September) or early (August) in the season. There is no good explanation for this increased longevity of the adults later in the season. There is no evolutionary benefit for the adults to live past the end of September, when the acorns mature, as laboratory reared females did not oviposit in mature acorns with a hardened shell. Calcote (1975) also found that pecan weevil adults did not oviposit into mature fruit. The timing of adult emergence and oviposition has to be closely timed with the development of acorns, which ensures survival of future generations of the insect. However, it was not determined, that shell hardness was the factor that prevented shell penetration and oviposition of laboratory reared adults in this study. Survival of larvae within an acorn is dependent on the size of the acorn and the nutritional needs of the larvae. The maximum number of young larvae found in one Garry oak acorn both in 1996 and 1998 was 10, and eight larvae in 1997. Potentially, the number of larvae per Garry oak acorn could be much higher since as many as 19 eggs were found in one acorn, although it has been reported that survival of larvae in the host decreases with increasing egg density (Butkewich et al. 1987). It is unlikely that all 10 larvae within one acorn would survive, because even two or three larvae can completely destroy the kernel of an acorn (pers. obs.), and four emergence holes was the maximum found in one acorn in all 3 years of the study. Swiecki et al. (1991) found up to eight filbert weevil larvae in one blue oak acorn (Quercus douglasii Hook. & Am.), although two or more larvae per acorn is more common (Sidney 1948, Anonymous 1990) in these 141 acorns, which are smaller than Garry oak acorns. Brezner (1960) reported that on average, only one larva is found in the small pin oak acorns. FILBERTWORM The infrequent observation of filbertworm eggs in this study may be due to several reasons. It has been documented that filbertworm adults also lay their eggs on foliage and branches (Dohanian 1944, AliNiazee 1981), as well as on acorns. Foliage and branches were not examined for the presence of eggs in this study. Also, the eggs of the filbertworm are very delicate and may have been damaged during collection, or after collection while they were stored in plastic bags in the refrigerator. Some authors have reported that only a single filbertworm larva is found in each infested acorn (blue oak) (Anonymous 1990, Swiecki et al. 1991). However, in this study, up to five larvae were found in a single acorn. As with the filbert weevil, it is not known if all five larvae could have obtained sufficient nutrients from one acorn to survive. However, It has been reported that filbertworm larva will leave an acorn before they are fully fed, and may enter two or three other acorns to complete development (Winston 1956). It is impossible to say if larvae found in the acorns in this study had entered the acorn from another acorn, or were still in the acorn in which the young larvae originally started feeding. 142 MANAGEMENT IMPLICATIONS Extensive control programs have been conducted in the U.S. on pecans (a high value crop) against Curculio spp. and Cydia latiferreana using chemical insecticides (Harris 1976, Schraer et al. 1998). In the past, chemicals such as DDT (Nickels 1950, Nickels 1952, Passon 1990), ethylene dibromide and carbofuran (Polles et al. 1973, Polles and Payne 1973, Tedders 1976), were widely used, much to the detriment of the environment. The application of the systemic insecticides phorate and Di-Syston® has been shown to increase the incidence of premature abscission of developing acorns (Dorsey et al.1962), although the reduction in infestation results in a net increase in the production of healthy acorns. The long-term effects of such an artificially increased acorn crop however, are not known, as populations of the filbertworm (and filbert weevil to a lesser extent) are linked to yearly fluctuations in the acorn crop. The finding in this study, that even moderately damaged Garry oak acorns have the potential to germinate, reduces the negative implications of high rates of acorn infestation. Therefore, I feel that control measures against the filbert weevil and filbertworm are not necessary. Any chemical control measures should be discouraged simply because of the complex relationship between the acorn crop, the insects inside the acorns and birds and mammals that eat the acorns. Since it has been found that blue jays may actually benefit from 143 consuming weevil infested acorns (Johnson et al 1993), reduction of the weevil larval population may have a detrimental effect on blue jays. The use of parasitoids to reduce infestation of acorns by the filbert weevil and filbertworm does not seem to be a viable option. Unfortunately, no parasitoids of either the filbert weevil, or the filbertworm were reared in this study. Although native parasitoids of both the filbert weevil and the filbertworm have been reared in the past, these parasitoids do not contribute substantially to decreases in the insect population (Brooks 1910, Thompson 1938, Dohanian 1940, Muesbeck et al. 1951, Brezner 1960, Gibson 1969, Harp and Vancleave 1976d, Kearby et al. 1986). The use of introduced parasitoids as biological control agents would require years of study and considerable expenditure to determine the effects of the introduced parasitoids on the complex Garry oak ecosystem. The most feasible way to ensure that future generations of seedlings are produced is through efforts of collection and manual planting of healthy seedlings. 144 LITERATURE CITED Agriculture Canada Expert Committee on Soil Survey. 1987. The Canadian system of soil classification. 2nd ed. Agriculture. Canada Publishing. 1646. 164 pp. AliNiazee, M. T. 1980. Insect and mite pests of filberts. Oregon Agricultural Experiment Station Bulletin, 643, p. 2-6. . 1981. Biology and control of the filbertworm, Melissopus latiferreanus. Proceedings of the Nut Grow Society of Oregon, Washington, and BC. Tigard, Oregon.: The Society. 66th p. 101-103. . 1983. A degree day method for predicting the filbertworm emergence. Proceedings of the Nut Grow Society of Oregon, Washington, and BC. Tigard, Oregon.: The Society. 68th p. 37-39. Alverson, D.R., M.K. Harris, C.E. Blanchard, and W.C. Hanlin. 1984. Mechanical impedance of adult pecan weevil (Coleoptera: Curculionidae) emergence related to soil moisture and penetration resistance. Environmental Entomology. 13:588-592. Andersson, C. 1992. The effect of weevil and fungal attacks on the germination of Quercus robur acorns. Forest Ecology and Management. 50: 247-251. Anonymous. 1948. Woody-plant seed manual. U.S. Department of Agriculture. Miscellaneous Publication No. 654. Pp. 297-304. Anonymous. 1990. Disease and insect impacts on life stages of blue oak. Fremontia. 60pp. Armstrong, T. 1958. Life history and ecology of the plum Curculio, Conotrachelus nenuphar (Hbst) (Coleoptera: Curculionidae), in the Niagara Peninsula, Ontario. Canadian Entomologist. 90:8-17. Association of Official Seed Analysts. 1978. Rules for testing seeds. Journal of Seed Technology. 6:1-126. Ballardie, R. T., and R.J. Whelan. 1986. Masting, seed dispersal and seed predation in the cycad Macrozamia communis. Oecologia. 70:100-105. Barrett, L.I. 1931. Influence of forest litter on the generation and early survival of chestnut oak, Quercus montana. Wildl. Ecology. 12: 476-484. Barnett, R.J. 1977. The effects of burial by squirrels on germination and survival of oak and hickory nuts. American Midland Naturalist. 98:319-330. 145 Bate-Smith, E.C. 1973. Haemanalysis of tannins: the concept of relative astringency. Phytochemistry, 12:907-912. Beal, J.A. 1952. The more important insects of Duke forest and the Piedmont Plateau. In: Forest Insects of the Southeast. Duke University School of Forestry Bulletin. 44: 18-24. Beck, D.E. 1977. Twelve-year acorn yield in southern Appalachian oaks. U.S.D.A. For. Serv. Res. Note SE-244. Southeast Forestry Experimental Station, Asheville, N.C. 8pp. Bedard, W.D. 1933. The number of larval instars and the approximate length of the larval stadia of Dendroctonus pseudotsugae Hopk., with a method for their determination in relation to other bark beetles. Journal of Economic Entomology. 26: 1128-1133. Bennett, S.E. 1965. Tannic acid as a repellent and toxicant to alfalfa weevil larvae. Journal of Economic Entomology. 58: 372. Bernays, E.A. 1981. Plant tannins and insect herbivores: an appraisal. Ecological Entomology. 6: 353-360. Bio-Serve Inc.. 1997. Insect rearing media and supplies 1997 catalog. Frenchtown, NJ. Boethel, D.J., R.D. Eikenbary, J.R. Bolte, CR. Gentry. 1974. Sampling pecan weevil nut infestations: effect of tree height and sector. Environ. Entomol. 3: 208-10. Bolsinger, CL. 1988. Hardwoods of California's timberlands, woodlands and Savannas. USDA Forest Service. PNW RB-148 Bonner, F. T. 1984. Testing for seed quality in southern oaks. Research Note SO-306. USDA. Bonner, F. T., and J.A. Vozzo. 1987. Seed biology and technology of Quercus. USDA Forest Serv., Southern Forest Exp. Sta., New Orleans, Louisiana. General Technical Report. SO-66. 21pp. Borowicz, V.A. and S.A. Juliano. 1986. Inverse density-dependent parasitism of Cornus amomum fruit by Rhagoletis cornivora. Ecology. 67: 639-643. Bossema, I. 1979. Jays and oaks: an eco-ethological study of a symbiosis. Behaviour. 70:1-117. Boucher, D. H., and V.L. Sork. 1979. Early drop of nuts in response to insect infestation. Oikos. 33: 440-443. 146 Bramlett, D.L. 1972. Cone crop development records for six years in shortleaf pine. Forest Science. 18:31-33. Brezner, J. 1960. Biology, ecology, and taxonomy of insects infesting acorns. Mo Agricultural Experimental Station Research Bulletin 726:1-40. Brooks, F.E. 1910. Snout beetles that injure nuts. West Va. Agricultural Experimental Station Bulletin 128:143-185 Brown, L. R., and CO. Eads. 1965. A technical study of insects affecting the oak trees in Southern California. Calif. Agric. Exp. Stn. Bull. 810. Butkewich, S.L., R.J. Prokopy, and T.A. Green. 1987. Discrimination of occupied host fruit by plum curculio females (Coleoptera: Curculionidae). Journal of Chemical Ecology. 13: 1833-1840 Calcote, V.R. 1975. Pecan Weevil: feeding and initial oviposition as related to nut development. Journal of Economic Entomology 68: 4-6. Casey, T.L. 1897. Coleopterological notices Vll. Annuals of the New York Academy Science. 9: 655-64. Chapman, R.F. 1974. The chemical inhibition of feeding by phytophagous insects: a review. Bulletin of Entomological Research. 64: 339-363. Chittenden, F.H. 1927. Classification of the nut curculios, (formerly Balaninus) of Boreal America. Entomology America. 7:129-208. Coward, G. 1992. The tree book: learning to recognize trees of British Columbia. Forestry Canada and Forest Service Information Division. Pp. 42. Crawley, M.J. 1992. Seed predators and plant population dynamics. In: Seeds: The ecology of regeneration in plant communities. Ed M. Fenner. Redwood Press Ltd. Pp. 165-191. Crawley, M. J., and CR. Long. 1995. Alternate bearing, predator satiation and seedling recruitment in Quercus robur L. Journal of Ecology. 83: 683-696. Crisswell, J.T., D.J. Boethel, R.D. Morrison, and R.D. Eikenbary. 1975. Longevity, puncturing of nuts and ovipositional activities by the pecan weevil on three cultivars of pecans. Journal of Economic Entomology. 68: 173-177. Cypert, E. and B.S. Webster. 1948. Yield and use by wildlife of water and willow oaks. Journal of Wildlife Management. 12: 227-231. Darley-Hill, S. and W.C Johnson. 1981. Acorn dispersal by the blue jay (Cyanocittacristata). Oecologia. 50: 231-232. 147 Davidar, P., and E.S. Morton. 1986. The relationship between fruit crop sizes and fruit removal rates by birds. Ecology. 67: 262-265. Dennis, W. 1930. Rejection of wormy nuts by squirrels. Journal of Mammalogy. 11: 195-209. Dohanian, S. M. 1940. Melissopus latiferreanus as a pest of filberts in the northwest. Journal of Economic Entomology. 33: 852-856. Dohanian, S.M. 1944. Control of the filbertworm and filbert weevil by orchard sanitation. Journal of Economic Entomology. 37: 764-766. Dorsey, C. K., E.H. Tyron, and K.L. Carvell. 1962. Insect damage to acorns in West Virginia and control studies using granular systemic insecticides. Journal of Economic Entomology. 55: 885-888. Downs, A.A. 1944. Estimating acorn crops for wildlife in the southern Appalachians. Journal of Wildlife Management. 8: 339-340. Downs, A.A., and W.E. McQuilkin. 1944. Seed production of southern Appalachian oak. Journal of Forestry. 42: 913-920. Dryer, H. G. 1890. The number of moults in lepidopteran larvae. Psyche. 5: 420-422. Dupree, M., and T.L Bissell. 1965. Observations of the periodic emergence of the pecan weevil. Proceedings of the south eastern Pecan Growers Association. 58: 50-1. Dutcher, J.D. and J.A. Payne. 1986. Pecan weevil (Curculio caryae, Coleoptera: Curculionidae) bionomics: a regional research problem. USDA Miscellaneous publication. Duvendeck, J. P. 1962. The value of acorns in the diet of Michigan deer. Journal of Wildlife Management. 26: 371-379. Eikenbary, R.D., and H.G. Raney. 1973. Intratree dispersal of the pecan weevil. Environmental Entomology. 2: 927-930. Ellison,R.L, and J.N. Thompson. 1987. Variation in seed and seedling size: the effects of seed herbivores on Lomatium gray! (Umbelliferae). Oikos, 49: 269-280. Erickson, W. 1996. Classification and interpretation of Garry oak (Quercus garryana) plant communities and ecosystems in southwestern British Columbia. M.Sc. thesis, University of Victoria. 148 Farmer, R.E. 1982. Variation in seed yields of white oak. Forest Science. 27: 377-380. Feeny, P.P. 1968. Effects of oak leaf tannins on larval growth of the winter oak moth Operophtera brumata. Journal of Insect Physiology. 14: 805-817. . 1969. Inhibitory effect of oak leaf tannins on the hydrolysis of proteins by trypsin. Phytochemistry. 8: 2119-2126. . 1970. Seasonal changes in oak leaf tannins and nutrients as a cause of spring feeding by winter moth caterpillars. Ecology. 51: 565-581. . 1976. Plant apparency and chemical defense. Recent Advances in Phytochemistry. 10:1-40. Fenner, M. 1991. Irregular seed crops in forest trees. Quarterly Journal of Forestry. 85:166-172. Feret, P.P, R.E. Kreh, S.A. Merkel, and R.G. Oderwald. 1982. Flower abundance, premature acorn abscission, and acorn production in Quercus alba L. Botanical Gazette. 143:216-218. Fleck, D.C. and J.N. Layne. 1990. Variation in tannin activity of acorns of seven species of central Florida oaks. Journal of Chemical Ecology. 16: 2925-2934. Forbes, E.B., LF. Marcy, A.L. Voris, and C.E. French. 1941. The digestive capabilities of the white-tailed deer. Journal of Wildlife Management. 5: 108-114. Franklin, J.F. and CT. Dryness. 1973. Natural vegetation of Oregon and Washington. U.S. Deptartement of Agriculture Forest Service, General Technical Report. PNW-8. Portland, Org. Freeland, W.J., and D.H. Janzen. 1974. Strategies in herbivory by mammals: the role of plant secondary compounds. American Naturalist. 108: 269-289. Fuchs, M.A. 1998. Seedling ecology of Garry oaks in British Columbia and dispersal of Garry oak acorns by Steller's jays. M.Sc. Thesis. University of British Columbia. Gaines, J.C. and F.L. Campbell. 1935. Dyar's rule as related to the number of instars of the corn ear worm, Heliothis obsoleta (Fab.), collected in the field. Annals of the Entomological Society of America. 28: 445-461. Gibson, L. P. 1964. Biology and life-history of acorn-infesting weevils of the genus Conotrachelus (Coleoptera: Curculionidae). Annals of the Entomological Society of America. 57: 521-526. 149 _. 1969. Monograph of the genus Curculio in the New World Part I. United States and Canada. In: Miscellaneous Publication 6, Entomological Society of America p. 239-285. . 1971. Insects of Bur oak acorns. Annuals of the Entomological Society of America. 64:232-234. . 1972. Insects that damage White Oak acorns. US Forest Service Research Paper Northeast Forest Experimental Station. No. NE-220, pp.7. . 1982. Insects that damage northern red oak acorns. Research paper, forest service USDA No. NE-492, 6pp. Glendenning, R. 1944. The Garry oak in British Columbia; an interesting example of discontinuous distribution. Canadian Field-Naturalist. 58: 61-5. Goldstein, J.L. and T. Swain. 1963. Changes in tannins in ripening fruits. Phytochemistry. 2: 371-383. . 1965. The inhibition of enzymes by tannins. Phytochemistry. 4: 185-192. Goodrum, P.D., V.H. Reid and C.E. Boyd. 1971. Acorn yields, characteristics and management criteria of oaks for wildlife. Journal of Wildlife Management. 35: 520-532. Griffin, J.R. 1971. Oak regeneration in the upper Carmel Valley, California. Ecology. 52: 862-868. Gysel, L. W. 1957. Acorn production on good, medium and poor sites in southern Michigan. Journal of Forestry. 55: 570-574. Hagel, R. 1999. Personal Communication. Natural Resources Canada. Pacific Forestry Center, Victoria, BC. Harlow, W.M., and E.S. Harrar. 1968. Textbook of Dendrology. McGraw-Hill. Pp. 291-313. Harp, S.J., and H.W. Van Cleave. 1976a. Biology of the pecan weevil. Southwest Entomol. 1: 21-30 . 1976b. Biology of the subterranean life stages of the pecan weevil in two soil types. Southwestern Entomol. 1: 31-34. . 1976c. Evidence of diapause in the pecan weevil. Southwestern Entomol. 1:35-37. . 1976d. New records of natural enemies of the pecan weevil. Southwestern Entomol. 1: 38-39. 150 Harper, J.L. 1977. Population biology of plants. Academic Press, London, England. Harris, M.K. 1976. Pecan weevil infestations of pecans of various sizes and infestations. Environmental Entomology 5: 248-250. Harris, M.K., and D.R. Ring. 1980. Adult pecan weevil emergence related to soil moisture. Journal of Economic Entomology. 73: 339-343. Henneberry, T.J., T. Meng Jr. and L.A. Bariola. 1990. Overwintering survival and emergence of boll weevils (CopeopteraL Curculionidae) in cotton bolls in Arizona. Journal of Economic Entomology. 83: 1879-1882. Horton, J.S. and J.T. Wright. 1944. The wood rat as an ecological factor in southern California watersheds. Ecology. 25:341-351. Hosie, R.C. 1973. Native trees of Canada. Canadian Forest Service. Crown Copyrights. Pgs. 184-186. Howe. H.F., and D. De Steven. 1979. Fruit production, migrant bird visitation and seed dispersal of Guarea glabra in Panama. Oecologia. 39: 185-196. Howe, H.F., and J.Smallwood. 1982. Ecology of seed dispersal. Annual Review of Ecology and Systematics. 13: 201-228. Janzen, D.H. 1969. Seed eaters versus seed size, number, toxicity and dispersal. Evolution. 23:1-27. . 1971. Seed predation by animals. Annual Review of Ecology and Systematics. 2: 465-492. Jones, E. W. 1959. Quercus L. Biological flora of the British Isles. Journal of Ecology. 47: 169-222. Johnson, W. C, L. Thomas, and CS. Adkisson. 1993. Dietary circumvention of acorn tannins by blue jays. Oecologia. 94:159-164. Kaushal, B.R., M.C. Pant, S. Kalia, Joshi, and R. Bora. 1993. Aspects of the biology and control of three species of acorn infesting oak acorns in Kumaun Himalaya. Journal of Applied Entomology. 115:388-397. Keen, F. P. 1958. Cone and seed insects of western forest trees. USDA Technical Bulletin 1169. p. 43,145-146. Kearby, W. H., D.M. Christisen, and S.A. Myers. 1986. Insects: Their biology and impact on acorn crops in Missouri's upland forests. Missouri Department of Conservation Terrestrial Series 16. 151 Koening, W. D., R.L. Mumme, W.J. Carmen, and M.T. Stanback. 1994. Acorn production by oaks in central coastal California: Variation within and among years. Ecology. 75: 99-109. Korstain, C. F. 1927. Factors controlling germination and early survival in oaks. Yale University School Forestry Bulletin 19:1-115. LeConte, J.L. 1857. U.S. Pacific Railroad report of exploration and surveys. Zoology. Part 3(1): 57-58 Levin, D.A. 1976. Chemical defenses of plants to pathogens and herbivores. Annual Review of Ecology and Systematics. 7: 121-159. Lewis, V. R. 1989. Host-interactions in the California oak-coast live oak ecosystem. Ph.D. University of California, Berkeley. . 1992. Within-tree distribution of acorns infested by Curculio occidentis and Cydia latiferreana. Environmental Entomology. 21: 975-982 Malliard, J. 1931. Redwood chickaree testing and storing hazelnuts. Journal of Mammalogy. 72:513-517. Marquis, D. A. P.L. Eckert, and P.A. Roach. 1976. Acorn weevils, rodents and deer all contribute to oak-regeneration difficulties in Pennsylvania. USDA Forest service research paper, Northeastern forest experiment station. No. NE-356, 5pp. 6 ref. Martin, J.S., and M.M. Martin. 1982. Tannin assays in ecological studies: lack of correlation between phenolics, proanthocyanidins, and protein-precipitating constituents in mature foliage of six oak species. Oecologia. 54: 2205-211. Matsuda, K. 1982. Studies on the early phase of the regeneration of a Konara oak {Quercus settata Thunb.) secondary forest I. Development and premature abscissions of Konara oak acorns. Japanese Journal of Ecology. 32: 293-302. McMinn, R.G., S. Eis, H.E. Hirvonen, ET. Oswald, and J.P. Senyk. 1976. Native Vegetation in British Columbia's Capital Region. Environment Canada, Forestry Service Report BC-X-140. McQuilkin, R.A., and R.A. Musbach. 1977. Pin oak acorn production on green tree reservoirs in southeastern Missouri. Journal of Wildlife Management. 41: 218-225. Meidinger, D. and J. Pojar. 1991. Ecosystems of British Columbia. BC Ministry of Forests Special Report Series 6. Menke, J. W. and M.E. Fry 1980. Trends in oak utilization - firewood, mast production, animal use. General Technical Report PSW-44 p.297-305. 152 Moore, L.A., and M.F. Willson. 1982. The effect of microhabitat, spatial distribution, and display size on dispersal of Lindera benzoin by avian frugivores. Canadian Journal of Botany. 60: 557-560. Muesebeck, C.F.W., K.V. Krombein and H.K. Townes, eds. 1951. Hymenoptera of America north of Mexico, synoptic catalog. U.S.D.A. Monog. No.2. Myers, S.A. 1978. Insect impact on acorn production in Missouri upland forests. Ph.D. Dissertation. University of Missouri.246 pp. Nichol,A.A. 1938. Experimental feeding of deer. University of Ariz. Agriculture Experimental Station, Technical Bulletin No. 75. 39pp. Nickels, CB. 1950. Experiments in control of the pecan weevil. Journal of Economic Entomology 43: 552-554. . 1952. Control of pecan weevil in Texas. Journal of Economic Entomology. 45: 1099-1100. Nilsson, S. G. 1985. Ecological and evolutionary interactions between reproduction of beech Fagus silvatica and seed eating animals. Oikos. 44:157-164. Nuszendorfer, F.C, K. Klinka, and D.A. Demarchi. 1991. Coastal Douglas-fir zone. In Ecosystems of British Columbia. Eds. Meidinger and Pojar. BC Ministry of Forests Special Report Series 6. Pp. 81-111. Oliver, A.D., and J.B. Chapin. 1984. Curculio fulvus (Coleoptera: Curculionidae) and its effects on acorns of live oaks, Quercus virginiana Miller. Environmental Entomology. 13: 1507-1510. Olson, D.F. Jr. 1974. Seeds of the woody plants in the United States. U.S. Department of Agriculture. Agriculture handbook no. 450. Passon, D. E. 1990. Controlling the filbert moth. Proceedings of the Nut Growers Society of Oregon, Wash, and BC. Tigard, Oregon: The Society. (75th) p. 111-113. Peacock, J.W., S.L. Wright and J.R. Galford. 1988. Attraction of the acorn-infesting Cydia latiferreana (Lepidoptera: Tortricidae) to pheromone-baited traps. Great Lakes Entomologist. 21: 151-156. Pojar, J. and A. MacKinnon. 1994. Plants of coastal British Columbia including Washington, Oregon & Alaska. BC Ministry of Forests and Lone Pine Publishing. Polles, S.G, and J.A. Payne. 1973. Pecan weevil: toxicity of insecticides in lab tests. Journal of Economic Entomology. 66: 479-498. 153 Polles, S.B., J.A. Payne and E.J. Wehunt. 1973. Pecan weevil: control with soil-applied insecticides and nematicides. Journal of Economic Entomology. 66: 501-503. Price, J.R., J.E. Slosser, and G.J. Puterka. 1985. Factors affecting survival of boll weevils in winter habitat in the Texas rolling plains. Southwestern Entomologist. 10: 1-6. Pucat, A.M. 1994 Filbertworm. Agriculture and Agri-Food Canada. Plant Health Risk Assessment Unit. Raney, H. G., and R.D. Eikenbary. 1969. A simplified trap for collecting adult pecan weevils. Journal of Economic Entomology 62: 722-723. Reid V.H. and P.D. Goodrum. 1957. Factors influencing the yield and wildlife use of acorns. In: Special problems in southern forest management. Proceedings of the sixth annual forestry symposium, April 4-5 1957. Pp. 46-79. Ricca, M.A., F.W. Wecherly, and R.D. Semitsch. 1996. Effects of soil moisture and temperature on overwintering survival of Curculio larvae (Coleoptera: Curculionidae). American Midland Naturalist. 136:203-206. Robbins, C.T., S. Mole, A.E. Hagerman and T.A. Hanley. 1987a. Role of tannins in defending plants against ruminants: reduction in protein availability. Ecology. 68:98-107. Robbins, C.T., S. Mole, A.E. Hagerman and T.A. Hanley. 1987b. Role of tannins in defending plants against ruminants: reduction in dry matter digestion. Ecology. 68: 1606-1615. Schettler, S. and M.N. Smith. 1980. Nursery propagation of California oaks. In: Plumb, T.R., tech coord. Proceedings of the symposium on the ecology, management, and utilization of California oaks: June 26-28, 1979, Claremont, CA. Gen Tech. Rep. PSW-44. Berkeley California: Pacific Southwest Forest and Range exp. Stn., Forest Service, USDA: 143-148. Schraer, S.M., M. Harris, J.A. Jackman, and M. Biggerstaff. 1998. Pecan weevil (Coleoptera: Curculionidae) emergence in a range of soil types. Environmental Entomology. 27:549-554. Semel, B., and D.C. Andersen. 1988. Vulnerability of acorn weevils (Coleoptera : Curculionidae) and attractiveness of weevils and infested Quercus alba acorns to Peromyscus leucopus and Blarina brevicauda. American Midland Naturalist. 119:385-393. Sharp, W. M., and H.H. Chisman. 1961. Flowering and fruiting in the white oaks. I. Staminate flowering through pollen dispersal. Ecology. 42: 365-372. 154 Sharp, W. M., and V.G. Sprague. 1966 Flowering and fruiting in the white oaks. Pistillate flowering, acorn development, weather, and yields. Ecology. 48:243-251. Sidney, C. 1948. Acorn weevils of the North Carolina Piedmont: Their biology and method of sampling infestation. M.A. Thesis. Duke University. 70 pp. Silverton, J.W. 1980. The evolutionary ecology of mast seedling in trees. Biological Journal of the Linnean Society. 14: 235-250. Slosser, J.E. and T.W. Fuchs. 1991. Overwintering survival of boll weevils (Coleoptera: Curculionidae) in the Texas rolling plains. Environmental Entomology. 20: 877-881. Smallwood, P.D., and W.D. Peters. 1986. Grey squirrel food preferences: the effects of tannin and fat concentrations. Ecology. 67: 168-174. Smith, CC. and D. Follmer. 1972. Food preferences of squirrels. Ecology. 53: 83-91. Sork, V. L. 1987. The effects of predation and light on seedling establishment in Gustavia superba. Ecology 68: 1341-1350. Sork, V. L, and D.H. Boucher. 1977. Dispersal of sweet pignut hickory in a year of low fruit production, and the influence of predation by a Curculionid beetle. Oecologia. 28: 289-299. SPSS. 1998. SPSS Advanced and base statistics 9.0. SPSS Inc., Chicago, IL. Stapanian, M.A. 1982. A model for fruiting display: seed dispersal by birds for mulberry trees. Ecology. 63: 1432-1443. Steele, M.A., L.Z. Hadj-Chikh, and J. Hazeltine. 1996. Catching and feeding decisions by Sciurus carolinensis: responses to weevil-infested acorns. Journal of Mammalogy. 77: 305-314. Steele, M.A, T. Knowles, K. Bridle, and E.L. Simms. 1993. Tannins and partial consumption of acorns: implications for dispersal of oaks by seed predators. American Midland Naturalist. 130: 229-238. Stein, W.I. 1990. Quercus garryana Dougl. Ex Hook. Pp. 650-660 in Burns, R.M. and B.H. Honkala, tech. Coords. Silvics of North America. Volume 2: Hardwoods. Agricultural Handbook 654. Forest Service, U.S. Department of Agriculture. Washington, DC. Stephenson, A.G. 1981. Flower and fruit abortion: proximate causes and ultimate function. Annual Review of Ecology and Systematics. 12: 253-279. 155 Stone, N.D., D.R. Rummel, S. Carroll, M.E. Makela and R.E. Frisbie. 1990. Simulation of boll weevil (Coleoptera: Curculionidae) spring emergence and overwintering survival in the Texas rolling plains. Environmental Entomology. 19: 91-98. Sudworth, G.B. 1908. Forest Trees of the Pacific Slope. U.S. Department of Agriculture, Forest Service, pp. 283-278. Swiecki, T. J., E.A. Bernhardt, and R.A. Arnold. 1991. Monitoring insect and disease impacts on range oaks in California. In Standiford, 1991. pp. 208-213. Tamas, I.A., D.H. Wallace, P.M. Ludford, and J.L. Ozbun. 1979. Effect of older fruits on abortion and abscisic acid concentration on younger fruits in Phaseolus vulgaris L. Plant Physiology. 64: 620-622. Tapper, P.G. 1992. Irregular fruiting in Fraxinus excelsior. Journal of Vegetation Science. 3:41-46. Tedders, W.L. 1976. Pesticides for pecan pests. Pecan south 3: 376-379. Thompson, B.G. 1938. Trichogramma evanescens Westwood, a parasite of Melissopus latiferreanus Wlshn. Journal of Economic Entomology. 31:129. Valentine, K.W.G., P.N. Sprout, T.E. Baker and L.M. Lavkulich. 1978. The soil landscapes of British Columbia. Resource analysis branch, Ministry of Environment, Victoria, British Columbia. Pp. 101-120. Wainio, W.W., and E.B. Forbes. 1941. The chemical composition of forest fruits and nuts from Pennsylvania. Journal of Agriculture Research. 62: 627-635. Waller, D. M. 1993. How does mast-fruiting get started? Trends in Ecology and Evolution. 8: 122-123. Weckerly, F.W., K.E. Nicholson, and R.D. Semlitch. 1989a. Experimental test of discrimination by squirrels for insect-infested and non-infested acorns. American Midland Naturalist. 122:412-415. Weckerly, F. W., D.W. Sugg, and R.D. Semlitsch. 1989b. Germination success of acorns (Quercus): insect predation and tannins. Canadian Journal of Forest Research. 19: 811-815. Wellington, W.G. 1950. Effect of radiation on the temperature of insects' habitats. Scientific Agriculture 30: 209-233. Williamson, M.J. 1966. Premature abcissions and white oak acorn crops. Forest Science. 12:19-21. 156 Winston, P.W. 1956. The acorn microsere, with special reference to arthropods. Ecology. 37: 120-132. 157 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0099321/manifest

Comment

Related Items