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Warren’s collar weevil in lodgepole pine stands in the Kispiox Forest District Byford, Geoffrey Thomas 1994

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WARREN’ S COLLAR WEEVILIN LODGEPOLE P1IIE STMDS INTHE KISPIOX FOREST DISTRICTbyGEOFFREY THOMAS BYFORDB.Sc., Simon Fraser University, 1988A THESIS SUBMITTED iN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Faculty ofForestry, Department ofForestSciences)We accept this thesis as conformingTHE UNIVERSITY OF BRITISH COLUMBIAJune 1994© Geoffrey Thomas Byford, 1994In presenting this thesis in partial fulfilment of the requirements for an advanced degree atthe University of British Columbia, I agree that the Library shall make it freely availablefor reference and study. I further agree that permission for extensive copying of this thesisfor scholarly purposes may be granted by the head of my department or by his or herrepresentatives. It is understood that copying or publication of this thesis for financialgain shall not be allowed without my written permission.Department ofFc-c ScitC6SThe University of British ColumbiaVancouver, CanadaDate_______________________ABSTRACTThe distribution and abundance of Warren’s collar weevil, Hylobius warreni Wood(Coleoptera: Curculionidae), was examined in lodgepole pine, Pinus contorta var. latfoliaEngelni, plantations in the Kispiox Forest District in north-central British Columbia. The effectof weevil feeding damage on height growth of dominant and co-dominant trees was alsoexamined. The weevil was found distributed throughout the forest district. All 31 surveyedplantations, ranging in age from 5 years to 16 years, had evidence of larval feeding damage.Weevil-caused mortality ranged from 0-8.8%. The average percentage of sampled trees attackedwas 29%. The percentage of trees attacked within a plantation was directly related to plantationage and average tree height. There was not a significant relationship between the thickness of theorganic layer above mineral soil and the percentage of trees attacked in the first year of the study.Plantation density had no apparent effect on the percentage of trees attacked. The highest levelsof weevil damage were found on circum-mesic, well drained sites in the ICHmc3 biogeoclimaticvariant. Plantations established on sites which originally had a pine component appeared to beparticularly susceptible to weevil damage. It appears that the collar weevil is not reducingplantations to below minimum stocking levels (<700 sph).The populations of the collar weevil found in 2 of the 3 intensively sampled plantations,ranging in age from 13-17 years old, were similarto those reported for naturally regeneratedstands of similar age in Alberta. One plantation had populations considerably higher than reportedelsewhere. This may have been due to a scarcity of lodgepole pine in the surroundingtimbertypes. The percentage of stems attacked within a diameter class increased proportionally withincreasing diameter class, and increasing basal area class.The percentage of the stem11circumference girdled increased with increasing root collar diameter and LFH layer depth. Thepercentage of lodgepole pine attacked within the 3 study sites ranged from 81 % to 92 %. Theseattack rates were higher than rates reported for naturally regenerated stands. This may have beendue to lower tree densities found in planted versus naturally regenerated stands. The highincidence of root collar weevil within the Kispiox Forest District may be related to a man-causedincrease in lodgepole pine within the area. This increase has occurred because of the conversionof mature mixed species coniferous stands to lodgepole pine plantations following clearcutting.Destructively sampled trees indicated that initial weevil attacks within plantations hadoccurred within the previous 6 years. The time of first attack was uniform within plots indicatingthat weevils were not dispersing from the stand margin. Results from stem analysis indicated thatheight growth of weevil damaged trees was not affected in the short term. The long term impactsof sub-lethal multiple weevil attacks and larval damage on height growth are not presently known.111TABLE OF CONTENTSPAGEAbstract iiTable of Contents ivList of Tables viList of Figures viiAcknowledgements ix1.0 Introduction 11.1 Warren’s Collar Weevil 21.2 Biology and Life History 41.3 Effects of Warren’s Collar Weevil at the tree level 51.4 Effects of Warren’s Collar Weevil at the stand level 71.5 Control 81.6 Susceptible sites 91.7 Progression of weevil infestations with stand age 101.8 Warren’s Collar Weevil in British Columbia 112.0 Methods 122.1 Study Area 122.2 Distribution and abundance ofWarren’s Collar Weevil 132.2.1 Selection of sampling method and plot type 132.2.2 Sampling intensity and maximum survey area 132.2.3 Plantation selection 152.2.4 Plot information 152.2.5 Plot summaries 172.2.6 Within plantation distribution 172.2.7 Historical information 192.2.8 Survey summary 19Iv2.3 Height growth and dispersal study 192.3.1 Study locations 192.3.2 Sampling methodology 212.3.3 Height growth study 223.0 Results 243.1 Distribution and abundance of Warren’s Collar Weevil 243.1.1 Selection of plot type 243.1.2 Plantation distribution 243.1.3 Plantation summaries 243.1.4 Weevil incidence in relation to site and stand factors 283.1.5 Within plantation distribution 333.1.6 Within district distribution 343.2 Height growth and dispersal study 343.2.1 Plot summaries 343.2.2 Pattern of attack 443.2.3 Stem analysis 444.0 Discussion 604.1 Distribution and abundance of Warren’s Collar Weevil 604.2 Height growth and dispersal study 675.0 Conclusions 726.0 Recommendations 74Bibliography 76VLIST OF TABLESPAGETable 1. Summary data for plantations surveyed for Hylobius warreniin the Kispiox Forest District, Hazelton B.C., Summer 1989 26Table 2. Number and percentage of sample trees attacked by Hylobius warreni,by host species, at Date Creek in the Kispiox Forest District, Summer 1990 35Table 3. Population estimates ofHylobius warreni and characteristics of attackedlodgepole pine trees at Date Creek in the Kispiox Forest District, Summer 1990 35Table 4. Number and percentage of sample trees attacked by Hylobius warreni, by hostspecies, at Mosquito Flats in the Kispiox Forest District, Summer 1990 40Table 5. Population estimates ofHylobius warreni and characteristics ofattacked lodgepole pine trees at Mosquito Flats in the Kispiox ForestDistrict, Summer 1990 40Table 6. Number and percentage of sample trees attacked by Hylobius warreni,by host species, at Shandilla in the Kispiox Forest District, Summer 1990 45Table 7. Population estimates ofHylobius warreni and characteristics of attackedlodgepole pine trees at Shandilla in the Kispiox Forest District, Summer 1990 45Table 8. Timing of attack ofHylobius warreni on sample trees in a 13 year oldlodgepole pine plantation at Date Creek in the Kispiox Forest District,Summer 1990 49Table 9. Timing of attack ofHylobius warreni on sample trees in a 17 year oldlodgepole pine plantation at Mosquito Flats in the Kispiox Forest District,Summer 1990 50Table 10. Timing of attack ofHylobius warreni on sampled trees in a 17 year oldlodgepole pine lantation at Shandilla in the Kispiox Forest District,Summer 1990 51Table 11. Stem analysis of lodgepole pine trees attacked by Hylobius warreni atDate Creek in the Kispiox Forest District, Summer 1990 53Table 12. Stem analysis of lodgepole pine trees attacked by Hylobius warreni atMosquito Flats in the Kispiox Forest District, Summer 1990 56Table 13. Stem analysis of lodgepole pine treesattacked by Hylobius warreni atShandilla in the Kispiox Forest District, Summer 1990 58viLIST OF FIGURESPAGEFigure 1. Schematic representation of the layout oftwo plot types tested forassessing the incidence ofHylobius warreni damage in the KispioxForest District, Hazelton, B.C., Summer 1989 14Figure 2. Summary plot map for a plantation surveyed for Hylobius warrenidamage in the Kispiox Forest District, Hazelton, B.C., Summer 1989 18Figure 3. Hylobius warreni study sites in the Kispiox Forest District, Summer 1990 20Figure 4. The distribution of pine plantations surveyed for Hylobius warrenidamage in the Kispiox Forest District, Hazelton, B.C., Summer 1989 25Figure 5. Age distribution of pine plantations surveyed for Hylobius warrenidamage, Kispiox Forest District, Summer 1990 27Figure 6. Percentage of sample lodgepole pine with Hylobius warrenidamagein relation to plantation age in the Kispiox Forest District, Summer 1990 29Figure 7. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to average tree height in the Kispiox Forest District, Summer 1990 30Figure 8. Percentage of sample lodgepole pine with Hylobius warrenidamagein relation to plantation density in the Kispiox Forest District, Summer 1990 31Figure 9. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to average organic matter layer depth inthe Kispiox ForestDistrict, Summer 199032Figure 10. Diameter distribution of sampled lodgepole pine trees and proportionattacked by Hylobius warreni at Date Creek in the Kispiox Forest District,Summer 199036Figure 11. Percentage of sample lodgepole pine withHylobius warreni damagein relation to root collar diameter at Date Creek in the Kispiox ForestDistrict, Summer 1990 37Figure 12. Percentage of sample lodgepolepine with Hylobius warreni damagein relation to average organic matter layer depthat Date Creek in theKispiox Forest District, Summer 1990 38Figure 13. Diameter distribution of sampled lodgepolepine trees and proportionattacked by Hylobius warreni at Mosquito Flats in the Kispiox Forest District,Summer 1990 41vi’Figure 14. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to root collar diameter at Mosquito Flats in the Kispiox ForestDistrict, Summer 1990 42Figure 15. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to average organic matter layer depth at Mosquito Flats in theKispiox Forest District, Summer 1990 43Figure 16. Diameter distribution of sampled lodgepole pine trees and proportionattacked by Hylobius warreni at Shandilla in the Kispiox Forest District,Summer 1990 46Figure 17. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to root collar diameter at Shandilla in the Kispiox ForestDistrict, Summer 1990 47Figure 18. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to average organic matter layer depth at Shandilla in theKispiox Forest District, Summer 1990 48Figure 19. Percentage of sample lodgepole pine with Hylobius warreni damagein relation to basal area class for three plantatations in theKispiox Forest District, Summer 1990 52Figure 20. Cumulative average tree height of lodgepole pine, in four Hylobius warrenigirdling classes, at Date Creek in the Kispiox Forest District, Summer 1990 54Figure 21. Cumulative average tree height of lodgepole pine, in four Hylobius warrenigirdling classes, at Mosquito Flats in the Kispiox Forest District, Summer 1990 57Figure 22. Cumulative average tree height of lodgepole pine, in four Hylobius warrenigirdling classes, at Shandilla in the Kispiox Forest District, Summer 1990 59VII’ACKNOWLEDGEMENTSI thank the Prince Rupert Region of the B.C. Ministry of Forests whose financialsupport made this thesis possible; specifically I thank Mr. Tim Ebata, RegionalEntomologist. I also thank the staff at the Kispiox Forest District for there support andservices; Ms. Barb Costerton, Mr. Jeff Lemieux, Mr. Andrew Reviakin, Mr. IanWilliamson, and Mr. Ian Wilson for there assistance in data collection. I thank the ScienceCouncil of British Columbia for financial support through the Graduate ResearchEngineering and Technology Award Program (G.R.E.A.T.). I would like to thank InteriorReforestation Co.Ltd for their support during the preparation of this thesis and Mr. JohnPrzeczek for providing comments on the manuscript. I thank the members of mycommittee: Dr. Peter Marshall, Dr. Tom Sullivan and Dr. Gordon Weetman. I would alsolike to thank Drs. Burton and Kozak. I am especially indebted to my Faculty Advisor, Dr.John McLean, whose patience and valuable advice have enabled me to complete thisthesis. Finally, I would like to thank my family for support throughout my scholasticcareer, especially my wife Jackie for her constant encouragement and unfailing support.ix1.0 INTRODUCTIONThe Kispiox Forest District lies within a coastal-interior transition zone in north-centralBritish Columbia. The vegetation exhibits characteristics of a coastal maritime climate and aninterior cordilleran climate (Haeussler et a!. 1985; Meidinger and Pojar 1991). As a result of thistransitional climate, the forest cover consists ofboth coastal and interior tree species. The majortree species include lodgepole pine (Pinus contorta var. latfolia Engelm.), hybrid spruce (Picea xglauca x sitchensis x engelmannii), sub-alpine and amabilis fir (Abies lasiocarpa (Hook.) Nutt.and A. amabilis (Dougl.) Forbes), western hemlock (Tsuga heterophylla (Raff.) Sarg.), westernredcedar (Thujaplicata Donn), trembling aspen (Populus tremuloides Michx), and paper birch(Betulapapyrfera Marsh.). The timber profile in the district has an overabundance ofmature/over-mature western hemlock and true fir timber types (>140 years old). More than 80%ofthe timber inventory consists of these two species (Ministry ofForests 1981). Timberallocation within the district has concentrated on harvesting these timber types in an attempt tominimize losses expected from insects, disease and windfall.Reforestation of harvested areas is usually achieved by planting spruce and lodgepole pine.Lodgepole pine is planted on drier sites and spruce is planted on wetter sites. The future forestprofile will consist of more spruce and pine than exists in the current inventory due to thereplacement of hemlock and true fir forests with these two species.Approximately 12 000 ha of pine have been planted in the Kispiox Forest District as of1988 (Ministry of Forests 1988). This figure is projectedto increase as more areas are harvested.Associated with this increase in the pine component of the profile is a potential increase of insectsand diseases which attack lodgepole pine. One such insect is Warren’s collar weevil (Hylobiuswarreni Wood .(Coleoptera: Curculionidae)).Ministry of Forests staff, Licensees and silviculture contractors have reported increasingincidence of this insect in lodgepole pine plantations within the Kispiox Forest District in recentyears. These increases were of concern because of the abundance of young lodgepole pine1plantations within the district. Of particular concern was the potential reduction in stocking dueto weevil caused mortality in young stands. As part of the Forest Resources DevelopmentAgreement (FRDA I:1985199O)1between the Province and the Federal government, funding wasmade available to assess the distribution and abundance ofWarren’s collar weevil in pineplantations within the district. The objective of the project was to provide a better understandingofthe relationship between Warren’s collar weevil and lodgepole pine plantations. The specificobjectives of the study were:1) To determine the distribution and abundance of Warren’s collar weevil in 6 to 16 year oldlodgepole pine plantations within the Kispiox Forest District.(2) To assess the impacts of weevil injury on the development of lodgepole pine stands to thefree-growing stage.(3) To determine if weevil incidence is related to predictable site or stand factors. A hazard mapcould be produced, using these factors to identify potential problem areas.(4) To determine timing of the first and subsequent attacks on planted lodgepole pine.(5) To determine the course of infestations within pine plantations.(6) To determine the impact of weevil feeding damage on the height growth of lodgepole pine.1.1 Warren’s Collar WeevilThe larvae of Warren’s collar weevil feed in the root collar region and on the larger lateralroots of a number of coniferous tree hosts (Fumiss and Carolin 1977). Hosts include variousspecies of pines, Pinus spp., spruces, Picea spp., true firs, Abies spp. and tamarack, Larix laricina(DuRoi) K.Koch (Warner 1966; Grant 1966). In western North America, the primary hostspecies is lodgepole pine, while white spruce (Picea glauca (Moench) Voss) is an alternate andless preferred species (Reid 1952; Stark 1959; Cerezke 1969). Larval feeding results in partial orcomplete girdling of the major lateral roots and the root collar of the host tree (Reid 1952).Intensive Forest Management Program - Brushing and Weeding and Pest-control Sub-program2Damage to the root collar region of the tree may cause death either directly or indirectly.Complete girdling of the phloem and cambium tissue at the root collar results in direct mortalitywhile indirect mortality may occur as a result of root decay flingi entering through the larvalwound (Warren 1956a; Stark 1959).Much of the early work on the biology ofWarren’s collar weevil and its relationship withits host tree species was done in the 1950’s and early 1960’s in Manitoba, Saskatchewan andAlberta (Warren and Whitney 1951; Whitney 1952; Reid 1952; Warren 1956a-c, 1958; Stark1959; Whitney 1961). During this period, the taxonomy ofthe genus was being clarified by anumber of researchers (Wood 1957; Warren 1960; Finnegan 1961; Wilson eta!. 1966; Warner1966).Warren’s collar weevil was first recognized as a distinct species by Wood (1957). Prior tothis, it was identified as Hypomolyxpiceus (De 0.). Wood separated H. piceus into two distinctspecies: Hylobius warreni and Hylobiuspinicola (Couper). The primary basis for the separationwas wing form. H. warreni has vestigial wings and is a flightless species while H. pinicola hasfhnctional wings.The majority of our current knowledge regarding Warren’s collar weevil was obtainedthrough the work of Dr. Herb Cerezke in Alberta during the 1960’s and early 1970’s. Hepublished a number of papers including works on the basic biology of the weevil, its effect on hosttrees, and its population dynamics in relation to forest management practices (Cerezke 1967,1969, 1970a-c, 1972, 1973a-b, 1974).31.2 Biology and Life History1.2.1 DescriptionWarren’s collar weevil is a relatively large dark brown to blackish beetle with white topale yellow scales or dots on the elytra (Wood 1957). They range in length from 11.7 mm to 15.1mm, with the females being slightly larger than the males. The sub-globose eggs are a translucentwhite and range from 0.5-0.8 mm (Duncan 1986). The larvae are creamy white with a tancoloured head capsule. They pass through six larval instars and a brief pre-pupal stage (Stark1959). The pupae are approximately 10 mm in length and appear much as the adults do.1.2.2 Life HistoryFemale weevils deposit eggs in the root collar region of susceptible trees from late June toAugust (Stark 1959; Cerezke 1969). The egg is deposited in a protective niche which isexcavated by the female and covered over with excrement (Warren and Whitney 1951; Cerezke1969). The larvae emerge an average of 42 days after oviposition (Cerezke 1969).After emerging, first instar larvae feed randomly on the phloem layer of host trees.However, as the larvae reach the second and third instars feeding becomes more circumferentiallyoriented and often extends into the cambium (Cerezke 1969). Depending on the time of eclosion,weevil larvae may overwinter as first to fourth instars (Stark 1959; Cerezke 1969). During thistime larvae are inactive, and do not commence feeding until the following spring. It is during thissecond year of larval feeding that the host tree sustains the majority of damage (Stark 1959;Cerezke 1969). Larvae overwinter a second time, usuallyas fifth or sixth instars.Larval wounding of the tree base results in the host tree exuding resin at the woundedarea. The larvae use the pitch to form a protective feeding gallery or tunnel. These tunnels arecomposed of a matrix of bark particles, frass and resin, and act as a barrier for the developinglarvae, protecting them from potential predators, parasites and dessication (Warren and Whitney1951; Warren 1956a; Cerezke 1969).4In the spring of the third year larvae feed briefly before constructing a pre-pupal chamber afew centimetres from the base of the tree. This chamber consists of a matrix of resin, frass andbark particles (Stark 1959; Cerezke 1969). The larvae spend a short time in the pre-pupal stagebefore pupating in June (Cerezke 1969).Adults emerge after a 4 week pupation period (Cerezke 1969). Adult emergence occursfrom late June through August (Warren and Whitney 1951; Stark 1959; Cerezke 1969). Theadults can survive for up to four years and they are reproductively mature for at least three years(Cerezke 1970a, 1973). They are nocturnal and emerge from the duflat dusk and either disperseto find suitable host trees or ascend a host to feed in the crown (Cerezke 1969, 1970a). Theyfeed on needles and bark on the upper portion of the branches, and occasionally on the terminalbuds (Cerezke 1969; Warren 1956a; Stark 1959). Adults may also feed on the bark of small roots(Warren and Whitney 1951). Adult feeding rarelycauses significant damage but may cause theterminal shoots to become twisted and distorted (Cerezke 1969). Dispersal is ambulatory, asWarren’s collar weevil has lost the capability for flight (Wood 1957; Warren 1960; Cerezke1969).1.3 Effects of Warrren’s Collar Weevil at the TreeLevelWarren’s collar weevil may affect its host tree in a number of ways. Larval feeding mayresult in direct tree mortality due to mechanicalinjury of the root collar (Warren 1 956c). Indirectmortality may result through windthrow of attacked trees whose roots havebeen weakened bylarval injury (Cerezke 1969). Indirect mortalitymay also occur through attack by secondaryconiferophagous insects, or fungi, invading a tree weakenedby larval damage (Warren andWhitney 1951; Smerlis 1957; Whitney 1961). Weevildamage may also cause growth reductionsand changes in the anatomical structure ofattacked trees (Cerezke 1969, 1970c, 1972, 1974).2Organic layer above mineral soil51.3.1 MortalityThe most evident effect of Warren’s collar weevil larval feeding is direct mortality of thehost tree. Generally, direct mortality occurs in trees less than 30 years old, and rarely occurs inmature trees (Warren 1956a; Cerezke 1969, 1970a-b, 1974). The reason for this is twofold.First, in younger trees larval feeding tends to be oriented circumferentially around the root collar,whereas in older, larger trees feeding tends to occur in patches and on the larger lateral roots(Cerezke 1970a). The feeding pattern in younger trees causes the flow of nutrients from thecrown to the roots to be severed, resulting in root and tree death. In older trees there is often astrip of undamaged bole which continuesto supply the roots with nourishment through theundamaged phloem tissue. Second, the more mature roots of older lodgepole pine may be moreresistant to weevil feeding than those of younger trees (Cerezke 1970b). There is also evidencethat older trees may repair tissue damagecaused by root collar weevil larvae (Cerezke 1969).Larval wounding may pre-dispose trees to attack by secondary organisms. Warren andWhitney (1951) found that larval wounds acted as infection courts for the entrance of the root rotfungi Armillaria and Polyporus in white spruce. It is these secondary organisms whichcause treedeath. There is little evidence of any association between root rots, or other decay fungi, andHylobius wounds in lodgepole pine (Stark 1959; Cerezke 1969).Mortality may also be caused bysecondary bark beetle colonization of weevil-injured trees. The expenditure of energyby the treesto pitch-out weevils and repair larval wounds may reduce their ability to defend against other treefeeding organisms (Coulson and Witter 1984). Larval feeding may also weaken the trees rootsystem to such a degree that it becomes susceptible to windthrow or snowpress (Duncan 1986).1.3.2 Anatomical EffectsWeevil injured trees have a number of ways of compensating for tissue injury. They mayincrease the radial growth of wood on both the girdledand non-girdled portions ofthe stem tocompensate for loss of strength on the wounded portion. This may occuras a °budding” type ofgrowth which seals off the damaged area and increasesthe area of conductive tissue (Cerezke1974). The tree may also respondto weevil injury by producing traumatic vertical resin ducts in6the growth rings directly above the wounded portion of the stem (Cerezke 1972). This greatlyincreases the supply of resin to the injured area and may be an attempt by the tree to “pitch-out”the weevil larvae. Although the tree is rarely successful in pitching-out weevils, the flow of resinmay be beneficial in coating the wound and sealing offthe injured area from the spores ofpathogenic fungi. A third mechanism by which the host compensates for weevil injury is theproduction of adventitious roots above the girdled area (Cerezke 1969). These roots compensatefor the loss of conductive tissue below the wound and provide the crown of the tree with a partialsupply of water and minerals.1.3.3 Growth LossesPartial girdling at the root collar and on lateral roots may lead to significant reductions inboth radial and height increment (Cerezke 1969, 1970c, 1974). Losses of 17.16% in mean radialgrowth and 11.50% in mean height growth were recorded near Robb, Alberta in the second andthird years following 50% girdling of lodgepole pine stems (Cerezke 1970a). There were nosignificant differences in either radial or height growth between attacked and unattacked trees onan ancillary site near Grande Prairie (Cerezke 1 970c). Cerezke (1974) artificially girdled the rootcollars of lodgepole pine trees and found that there was a general decline in height growth withincreased circumference of the root collar girdled. Height increment decreased gradually until 60-80% of the root collar circumference had been girdled, after which there was a rapid decrease.However, losses in radial increment did not exceed 5% when compared with controls for a rangeof girdling classes between 0 and 90%.1.4 Effects of Warren’s Collar Weevil at the Stand LevelWarren’s collar weevil infestations have a number of consequences at the stand level.Mortality of individual or groups of trees may result in pockets ofNot Satisfactorily Restocked(NSR) areas within a stand (Herring and Coates 1981). Similar patches of windthrown orsnowpressed trees may also occur (Duncan 1986).7The primary impact ofH. warreni at the stand level is growth loss. The cumulative loss ofheight and/or diameter growth of individual stems must lead to reduced volume production withina stand. Stand level volume loss attributable to root collar weevil damage has not been quantified;however, Cerezke (1969) states that losses to dominant and co-dominant trees may beconsiderable on good growing sites.1.5 ControlThe strategies for controlling Warren’s collar weevil populations may be grouped into twobroad classes: chemical controls and silvicultural controls. Chemical controls are implementedafter stands have become infested, while silvicultural controls are designed to prevent weevilsfrom invading or re-invading a stand.1.5.1 Chemical ControlsDuring the 1950’s, ethylene dichloride was effective in killing larvae of Warren’s collarweevil and benzene hexachloride (Lindane©)was effective in preventing the re-invasion ofpreviously attacked trees (Warren 1 956a). These chemicals were applied directly to the base ofinfested trees and were extremely toxic. Carbosulfan granular insecticides have been used tocontrol a related Hylobius sp. in Europe (Castellano and Marsh 1987). These are also applieddirectly to the root collar of individual trees. The cost of this labour intensive activity limits theiruse to intensively managed, high value plantations, and precludes their use in more extensivelymanaged timber production plantations. . The negative impact of such chemicals on non-targetorganisms must also be considered.1.5.2 Silvicultural ControlsThe first step in implementing silvicultural controls for Warren’s collar weevil isidentifying high risk stands which are scheduled for harvest. After identification of susceptiblestands, it is necessary to develop a prescription which will reduce weevil populations in thesubsequent stand. The most effective means of reducing populations is through clearcut8harvesting and site preparation (Cerezke 1970a). Infested stands should be clearcut harvestedleaving no residual susceptible trees, and site prepared either with scarification or prescribedburning (Cerezke 1969, 1970a). Clearcut harvesting reduces weevil populations by up to 88%,and site preparation results in a further reduction of the residual population by removing orreducing the duff layer, which is critical for larval survival (Cerezke 1973b). Weevil populationsin the subsequent stand are reduced accordingly.There are also silvicultural controls which can be applied after weevils have invaded astand. These involve screefing the area around the base of infested trees and pruning the lowerbranches (Warren 1956a; Wilson 1967). Screefing removes the LFH layer at the root collar ofhost trees thus greatly reducing the weevil habitat. Pruning of the lower branches increases thelight and heat around the tree base. This dries out the LFH layer making it unsuitable foroviposition by adult females. As for chemical controls, pruning and screefing may be effective inhigher value stands but the, high labour costs make them unsuitable on an operational basis forlower value timber production plantations.1.6 Susceptible SitesThe relationship between forest site type and weevil abundancewas first recognized byWarren (1956a-b). He found that damage in spruce standsin Manitoba increased as the averagemoisture content of the humus layer increased. The highest population of Warren’s collar weevilwas found on a very wet site characterized by a peat layer overa gleyed soil. In B.C. and Alberta,the weevil is found on drier sites. Stark (1959) foundthe weevil distributed throughout theforested regions of Alberta, predominantly in the boreal forest. Cerezke (1969,1970a-b) furtherrefined the weevils site requirements. He found theweevil primarily on moist, rich sites within theboreal region. These were sites with good drainagecharacteristics, strong soil development andan abundance of herbaceous, moss and shrub species.In Alberta, the weevil shows a definitepreference for lodgepole pine stands (Cerezke 1970b). Standsat low elevations have a higherincidence of weevil damage than stands at higher elevations(>1600m).9In central British Columbia, plantations with the highest incidence of weevil were foundon coarse textured, well drained soils, while those found on wet sites with poor drainage were lessseriously affected (Herring and Coates 1981). In northwestern B.C., Garbutt (1988) found thatweevil damage was confined to trees within one biogeoclimatic variant, the ICHmc3 (i.e. Interior-Cedar-Hemlock, moist, cold- Lower Nass Basin) (Meidinger and Pojar 1991). Susceptible siteswithin this variant were circum-mesic sites with well drained soils.Warren’s collar weevil is found on sites containing a relatively thick duff layer composedof a mixture of moss and herb species (Cerezke 1970a). There was a strong relationship betweenthe depth ofthis layer at the tree base and the distribution ofweevils withina stand. In general,the number of weevils per tree increased as the thickness of the duff increased (Cerezke 1969).This relationship was stronger as tree size increased.1.7 Progression of Weevil Infestations with Stand AgeHost trees become susceptible to weevil attack between the ages of 6 and 16 years, whenthey reach a size of 1-1.5 m tall and 5 cm in diameterat stump height (30 cm) (Warren andWhitney 1951; Reid 1952; Cerezke 1969, 1 970a). Warren’s collar weevil attacks healthy,vigorous trees and shows a preference for dominant and co-dominants, although intermediate andsuppressed trees may also be attacked (Reid 1952). Once weevils become established ina standthey remain there until stand replacement (Warren and Whitney 1951; Reid 1952; Cerezke 1969).The initial infestation of a regenerating pine stand is believed to originate fromsurrounding older stands of a susceptiblehost species (Cerezke 1969). In 15-25 year oldlodgepole pine stands in Alberta, Cerezke (1969,1 970b) found that infestations spread intopineregeneration at a rate of 10-15 rn/year from adjacent infested mature pine. Treesat the peripheryof a plantation or naturally regeneratingcutbiock are attacked first, and the infestation proceedsinward as the population increases.Cerezke (1969) found an increase in attack incidence withinstands between the ages of 10 and 60 years. After 60years, the infestation rate levelled off whenup to 90% of trees within a stand had evidence of previousweevil injury. Generally, there is an10increase in the number of weevil larvae found on individual trees as stand age increases, howeverthe total population of larvae within a stand during its life remains relatively constant. This is dueto natural stand thinning processes which result in the same number ofweevils being concentratedon a fewer number of stems (Cerezke 1970c).The final stage in the cycle of a weevil population occurs when an infested stand isreplaced.. This can occur either by natural means such as wildfire, or by artificial means such asharvesting. Following clearcutting of infested stands, large increases in weevil populations insurrounding stands have been recorded (Cerezke 1969, 1973b). It is believed that surviving adultweevils migrate from the clearcut into surrounding trees. The adjacent timber, whether mature orimmature, provides suitable habitat to maintain populations of the weevil. This “reservoir”population then re-invades the regenerating stand once trees reach a susceptible size.1.8 Warren’s Collar Weevil in British ColumbiaIn British Columbia, outbreaks of Warren’s collar weevil have traditionally been sporadicand localized. Recently, however, populations of the weevil have been on the increase inlodgepole pine stands in the Prince George and Prince Rupert Forest Regions.The first report of the insect having adverse impacts on forest stands occurred in thePrince George Forest Region (Herring and Coates 1981). Warren’s collar weevil was found in 9of 11 lodgepole pine plantations. The percentage of living trees attacked ranged from 1.2% to5.0%, and the mortality rate ranged from less than 1% to 8.2%. They estimated an annualincrease of between 1.2% and 5.0% in the percentage of trees attacked within a plantation.Warren’s collar weevil has also increased in the Prince Rupert Forest Region in recentyears. Specifically, there have been increases inpopulations of the insect in lodgepole pineplantations near Hazekon (Garbutt 1988). An averageof 76% of 4 to 20 year old lodgepole pinetrees sampled in five plantations were infestedwith weevil larvae (Garbutt 1988).112.0 METHODSThe study was completed over two field seasons: from May 1989 to August 1989 andfrom May 1990 to August 1990. The first field season concentrated on assessing the distributionand abundance of Warren’s collar weevil within the Forest District. The second field seasonconcentrated on assessing the epidemiology of Warren’s collar weevil and the potential impact itmay have on the height growth of lodgepole pine.2.1 Study AreaThe study was done in the Kispiox Forest District in north-central British Columbia and allsurvey areas were in the Interior Cedar-Hemlock biogeoclimatic zone, moist cool biogeoclimaticsubzone (Meidinger and Pojar 1991). The climate is transitional between coastal and interiorinfluences. It is characterized by warm moist summers, cool wet falls, and cold winters. Theaverage precipitation ranges from 500 - 1200 mm per year. The average daily temperature rangesfrom -13.9°C for the coldest month to 22.5°C for the warmest month (Haeussler eta!. 1985).The majority of sites surveyed over the two year period were within the ICHmc3 variantof the subzone (Meidinger and Pojar 1991) (ICHg3 under the previous classification system(Haeussler et a!. 1985)). The major tree species include lodgepole pine, hybrid spruce, subalpinefir, amabilis fir, western hemlock, western redcedar, trembling aspen, and paper birch. As thename ofthe zone implies, hemlock and cedar are the true climatic climax species, however theirdistribution has been limited by a history of frequent natural fires and human disturbance.Because of this frequent disturbance, the variant is characterized by widespread seral stands ofaspen, paper birch, hazelnut (Corylus cornuta Marsh.) and other shrubs (Haeussler eta!. 1985).122.2 Distribution and Abundance of Warren’s Collar WeevilTo assess the distribution and abundance of Warren’s collar weevil in the Kispiox ForestDistrict, a representative sample of pine plantations within the district had to be surveyed. Thetarget plantations to survey were 5-to 16-year-old pine stands within the ICHmc3 variant(Meidinger and Pojar 1991), as these plantations were considered to be the most susceptible tocolonization by Warren’s collar weevil. Additionally, the target was to sample a minimum of 30pine plantations over the 4 month period.2.2.1 Selection of sampling method and plot typeBefore proceeding with the survey, an appropriate sampling method had to be chosen.Two plot types were selected for evaluation: a 2 m by 25 m strip plot adapted from Fletcher(1986) and a 3.99 m radius circular plot commonly used in B.C. Ministry of Forests silviculturesurveys. Both plot types had areas of 50 m2. A 4 ha area in a Date Creek plantation (Figure 1),known tobe infested by Warren’s collar weevil (Garbutt 1988), was selected for comparisontesting of the 2 plot types. Alternate transects of strip and circular plots were oriented in an East- West direction. Circular plot centres were placed at 25 m intervals while strip plots wereoriented sequentially along a transect, with 25 m between transects. The percentage of sampletrees with larval damage was determined for each plot type. Dominant and co-dominantlodgepole pine trees with either old or current weevil scarring were considered attacked. Thepercentage of sample trees attacked was pooled for all plots within each plot type and the twoplot types were compared using a Z statistic (Zar 1984).2.2.2 Sampling intensity and maximum survey areaLogistical constraints necessitated a maximum sampling intensity of 1% (2 plots/ha) forsurveyed plantations. This was to ensure that the sampling of the desired number of plantations13Figure 1. Schematicrepresentation ofthelayout oftwo plot types tested for assessing theincidence ofHylobiuswarreni damage in the Kispiox Forest District, Hazelton,B.C., Summer 1989.I.Scale: 1:10000Circular plots(3.99rn radius)I—I Strip plots(2rn X 25m)14was completed within the study timeframe (16 weeks). The maximum area surveyed within anyplantation was 50 ha. For plantations greater than 50 ha, an arbitrary 50 ha area was delineatedfor sampling. Approximately eight weeks into the project it became apparent that due to time,and budget constraints, the minimum number of plantations could not be surveyed using asampling intensity of 1 %. Therefore, the sampling intensity was reduced to 0.5% oftheplantation area (1 plot/ha) for the final 15 plantations.2.2.3 Plantation SelectionThirty plantations were selected randomly from a pooi of plantations meeting thefollowing criteria: they had to be predominantly pine(>50% of total stems), they had to be aminimum of 5 years old, and they had to meet the B.C. Ministry of Forests minimum stockingstandards (a minimum of 700 well spaced stems per hectare).2.2.4 Plot informationThe following information, was collected from each plot:i). The total # of trees within the plot, classified by species and age class, where 2 broadage classes were established: Layer 1 and layer 2 trees. Layer 1 trees included all speciesthat had seeded in naturally since the time of planting. Layer 2 trees were plantedlodgepole pine trees. Layer 2 trees were characterized by the average height and dbhvalues given for each plantationii) The # of dead lodgepole pine (P1) and spruce (Sx) and the cause of death from visiblesymptoms.iii) The # of dying or chiorotic P1 and thecause of stress from visible symptoms.iv) The # of green healthy looking pine with root collar weevil damage.v) The # of well-spaced trees per plot based on stem form and spacing (an arbitraryminimum 2 rn distance from competing conifers). The maximum # of well-spacedtrees/plot was 6.vi) The # of weevilled (evidence of old or new larval feeding damage) potential well15spaced stems (i.e., meet all requirements of v) and have evidence of weevil damage).vii) The average LFH depth (organic layer above mineral soil), calculated by taking 4depth samples every 4th plot. The plot was divided into 4 equal quadrants and ameasurement was taken from the centre of each. Sample depths were pooled and theaverage calculated for each plantation. LFH, as defined in this study, included all organicmatter above mineral soil including the moss layer, if present.Trees were recorded as weevil damaged if they had evidence of new or old attacks. Newattacks were distinguished from old attacks by the presence of fresh pitch exudation and/or thepresence of larvae.The average percentage of the stem circumference girdled by weevil larvae and theaverage number of larvae present per tree for each plantation were also determined for thoseplantations surveyed at the 0.5% intensity. This was done by arbitrarily selecting the first tree perplot with larval feeding damage and excavating the root collar and larger lateral roots. Thepercentage of the stem circumference girdled was estimated to the nearest 10%. The totalnumber of larvae per tree was also recorded.162.2.5 Plot SummariesEach plantation was summarized in terms of the following attributes:I) Total trees/haii) Total well-spaced trees/haiii) Total trees/ha with weevil damageiv) Total well-spaced trees/ha3with weevil damagev) % of weevil caused mortality to layer 2 pinevi) Total # of chiorotic and dead trees due to agents other than weevilvii) Average tree heightviii) Average diameter at breast height (dbh), where trees were at least 3 m in height.Average tree height and dbh values for each plantation were determined by measuring aminimum of 30 dominant / co-dominant lodgepole pine trees per plantation.The age of the dominant/co-dominant trees was assumed to be the same as the plantationage. This was confirmed by sampling a few trees per plantation with an increment borer and alsoby conducting whorl counts.2.2.6 Within Plantation DistributionA 1:10 000 or 1:20 000 scale plot map was produced for each plantation showing thedistribution of plots with and without weevilled trees (Figure 2). This was done to determine ifthere was any apparent stratification of weevil damage within a plantation. This was then3Well-spaced and weevilled well-spaced trees are not necessarily additive. A smaller non-weevilled tree would betallied as a well-spaced tree even if it was within 2 m of a taller weevilled tree. The weevilled tree would then betallied as a weevilled well-spaced tree. In the absence of weevil, only one well-spaced tree would have been tallied.17Kispiox Forest District1989 Warren’s collar weevilsurvey summaryOpening #: 93M032-005Location: N. of SalmonRiverDate surveyed: May 1989Scale: 1: 10000Figure 2. Summaryplot map for aplantation surveyedfor Hylobius warrenidamage inthe KispioxForest District,Hazelton, B.C.,Summer 1989.‘ITotal area (ha): 58Area surveyed (ha): 58$77History symbol:N81NI,I,III,‘II’I’I’LEGENDPo.C. A Pointof commencement• Plots withweeviled treeso Plots without weeviledtreesI’I’18compared with field information (i.e. plot notes) to determine the pattern of weevil attack withinthe sampled area.2.2.7 Historical InformationThe B.C. Ministry of Forests history record system provided historical backgroundinformation on surveyed plantations. This included information on original stand type, sitepreparation method, plantation establishment and, in some cases, ecosystem classification. Thisinformation was then used to determine if site history is usefhl in predicting weevil abundancewithin plantations.2.2.8 Survey SummaryAfter data compilation was completed for all plantations, simple linear regression (Zar1984) was used to determine the relationship between percentage of sample pine attacked, andplantation age, tree height, tree density and LFH depth. Regression analysis was done usingMIDAS (Fox and Guire 1976) on the University of British Columbia computing services network.2.3 Height Growth and Dispersal Study2.3.1 Study LocationsThe study was replicated at three locations within the Kispiox Forest District: Date Creek,Mosquito Flats, and Shandilla Creek (Figure 3). These locations had been surveyed in 1989 aspart of the distribution study and were knownto support weevil infestations. All plantations weresurveyed from May through August 1990. All plantations were within the ICHmc3biogeoclimatic variant (Meidinger and Pojar 1991).19_KISPIOXFOREST DISTRICTFigure 3. Hylobiuswarreni studysites in the Kispiox ForestDistrict, Summer 1990N202.3.1.1 Date CreekThis opening was clearcut logged in 1975 and was spot burned and planted in 1976. Theoriginal stand type was spruce-hemlock. The elevation is 457 m, the average slope is 20%, and ithas a southerly aspect. Stand density was estimated at 5455 sph in 1989 (first year of study),however a large portion of this density was relatively small natural seedlings which had ingressedsince planting. Lodgepole pine is the major species, while spruce is a minor component on wettermicrosites. Natural regeneration included western redcedar, western hemlock and true fir. The1989 survey found 45% of sampled trees had evidence of weevil feeding.2.3.1.2 Mosquito FlatsThis opening was clearcut logged and broadcast burned in 1972, and planted in 1973. Theoriginal stand type was hemlock-pine. The plantation was manually weeded in 1985 and fertilizedin the fall of 1989. The elevation is 487 m, the average slope is 10-20%, and the aspect west.Stand density was estimated at 1054 sph in 1989 (first year of study). Lodgepole pine is themajor species, with spruce making up a minor component. Natural regeneration included westernhemlock, western redcedar and some true fir. The 1989 survey found 84% of sampled trees hadevidence of weevil feeding.2.3.1.3 Shandilla CreekThis opening was clearcut logged in 1968, burned in 1969, 1970 and 1972, and planted in1973. The original stand type was hemlock-spruce. This plantation was fertilized in the fall of1989. The elevation is 381 m, the average slope is 50%, and theaspect north. Stand density wasestimated at 3095 sph in 1989 (first year of study). Lodgepole pine is the major species, withspruce making up a minor component. Natural regeneration includes western hemlock andwestern redcedar. The 1989 survey found 55% of sampled trees had evidence of weevil feeding.2.3.2 Sampling MethodologyA single rectangular plot 20 m wide and 150 m long (200 m long in the Date Creekplantation) extended perpendicularly from the stand margin into the plantation. The point ofcommencement for the plot was chosen for ease of location and proximityto mature timber21(preferably pine). Plot boundaries were located using a compass and 50 m nylon chain, and weremarked with flagging tape. The four corners ofthe plot were marked with wooden stakes and theP.O.C. was marked with a metal tag.Within each plot all pine and spruce trees were permanently numbered and tagged andsampled for the following parameters:i) Organic layer depth (LFH) at the root collar of all sampled trees. Two measurementswere taken on opposite sides of the tree and LFH depth was recorded as the mean of thesetwo values. Measurement location was arbitrary. Notes were also recorded on thecomposition of the LFH layer at the tree base and within the plantation, in general.ii) Root collar diameter.iii) Number and age of weevil life stages present.iv) Percentage of root collar circumference girdled for attacked trees. Girdles wereclassed as new or old: new attacks had fresh resin and larvae were present, while oldattacks were characterized by hard, whitish resin deposits.vi) Presence of other damaging organisms.2.3.3 Height Growth Study2.3.3.1 Tree SelectionAfter all trees were sampled and damage assessments were completed, the trees weregrouped into four girdling classes according to the amount of the root collar circumferencegirdled: 0%, 1-50%, 51-80% and 81-99% of the root collar girdled. The categories for the DateCreek plantation were 0%, 1-50%, 5 1-70%, and 71-99%. The girdling classes were changed forthe former two plantations in mid-project because it was felt that growth losses may become moreevident after 80% of the root collar has been girdled(Cerezke 1974). The five largest diametertrees in each class were selected for stem analysis.222.3.3.2 Stem AnalysisEach ofthe selected trees was felled and the internodal growth over the life of the treewas measured. Wooden discs were removed from the root collar and the years of weevil attackwere assessed using a starch staining method developed by Cerezke (1972). When injury to thecambium of the tree occurs, the tree responds by producing traumatic resin ducts. Thesetraumatic ducts show up as tangential bands in the annual rings in the years in which the damageoccurs, and can be used to determine the time of the injury. Using this method and the presenceof old weevil feeding scars, it was possible to determine when the tree was attacked.2.3.3.3 Statistical AnalysisAnalysis of variance (one-way) was used to compare girdling classes for differences inroot collar diameter, breast height diameter, and annual height increment. A Student-NewmanKeuls test was used to test for significant differences among means for these parameters (Zar1984). Annual height increments from 1979 to 1989 were tested for significant differencesbetween girdling classes for the Mosquito Flats and Shandilla plantations. Height incrementsbetween 1980 and 1989 were tested for significant differences between classes in the Date Creekplantation. Pre-1979 height increments for Mosquito Flats and Shandilla, and pre-1980 heightincrements for Date Creek were excluded from analysis to ensure that growth was relatively linearfrom year to year. Reliability of height measurements below breast height was somewhat suspect.233.0 RESULTS3.1 Distribution and Abundance of Warren’s Collar Weevil3.1.1 Selection of plot typeThere was no significant difference in the percentage of sampled trees with weevil damagebetween the 2 plot types (Z=0.176; p > 0.05). In strip plots, 46.3% of sampled stems hadevidence of weevil feeding. In circular plots, 45.2% of sampled stems had evidence ofweevilfeeding.3.1.2 Plantation distributionSurveyed plantations were distributed throughout the Kispiox Forest District (Figure 4).Plantations ranged in age from 5 to 16 years (Table 1, Figure 5). The average age of surveyedplantations was 9 years. Plantation size ranged from 4 ha to 107 ha. The average plantation sizewas 58 ha. The average area surveyed was 40 ha.3.1.3 Plantation summariesThe average % of sampled pine with Warren’s collar weevil larval damage was 29 %(S.D.=26%; Range:0-100%) (Table 1). The average % of sampled spruce with larval damagewas 1.4% (S.D.= 3.5%; Range: 0-15%). Weevil caused mortality was low in most plantations,averaging 1.5% (S.D.1.9%; Range:0-8.8%).The average percentage of the circumference of the root collar girdled of sampled treesfor the final 15 plantations was 50% (S.D.=32%, n=107) and the average number of larvae pergirdled tree was 0.33 (S.D.=0.49, n107).In most cases there were sufficient unattacked well spaced trees to maintain plantations atminimum stocking (20 of 31 plantations> 700 stemslha)(Table 1). Four of the eleven plantationswhich were below minimum stocking had less than 600 stems/ha.24FigUre 4. The distribution of pineplantations surveyed for Hylobius warreni damagein the Kispiox ForestDistrict, Hazelton, B.C., Summer1989KISPIOXFORESTDISTRICTNA Numberandlocation ofsurveyedplanLations25Table1.SummarydataforplantationssurveyedforHylobiuswarreniintheKispioxForestDistrict,HazeltonB.C.,Summer1989.LocationOpeningPlantationSiteEcosystemOriginalElevationSlopeAspectSoilLFHAreaSampling%1%WellWeevilled2TotalTreeDBH#AgePreparationClassificationStand(m)(96)Texture(cm)(ha)IntensityWeevilledWeevilSpacedWellTrees!Height(cm)Type(%)MortalityStems!haSpacedlhaha(m)Shandilla93M001-009W.ofSkeenax93M001-013NashV93M011-041SuskwaR.93M024-007SuskwaR.93M024-018MosquitoFlat93M024-025RobinsonLk.93M033-005NashV93M011-047SeelyLk.93M022-019SuslcwaR.93M024-005N.SalmonR.93M032-005UtsunCr.93M042-007DateCr.93M042-026N.KlineLk93M051-002MurderCr.93M051-006LOT302093M051-014CullonCr.93M061-016CullonCr.93M061-030IronsideCr.103P060-002IronsideCr.103P070-010IronsideCr.103P070-023StenittCr.93M052-023SalmonR.93M032-01ISalmonR.93M032-014NatlanCr.93M034-0055m.NashY93M011-045LunoCr.93M014-062SwanRd.93M032-007SterrittCr.93M052-0107Sisters103P009-011NangeeseR.103P079-005BroadcastburnICHg3.01109BroadcastburnlCHg2.01BroadcastburnICHg3.01!.09BroadcastburnICHg2-3BroadcastbumlCHg3.01BroadcastbumICHg3.01BroadcastburnICHg3.03a38150N45720N54910SE61015S45720N48710W88420N54910SE45020576210S3050F53410V45720S3900F58015SW54930W50010F45020S45010SW45015SE42520V45015SW3000F30015NW76220545010SW40020W27515V4505F46015N5500FSL750-750SL430-1550-1246-638-1114SL833-550SiL843SiL758SLILS750-54-850-742SL450CL750IJCL730L517SiCL750SL450L736LS528SiCL847C1350-650CIISL722SL-L64CILS849SL839LS6141551.16081340.56141751.02401270.37261711.14281841.317714306001231.210300.5350.14401342.28251421.4361166.310248452.47100.51907120.5121.68120.5230.36480.560.76880.5509000.5lOO28290.583.68960.56010120.541.49710.5228.88561346.07631308881120.39021174.08230.53108000.5317780.5008560.58081449230957.0410.121428946.468.154028607.3210.520217506.379.340529597.459.556410545.0710.325018846.8910.127265203.604.746469444.094.513826664.165.735727304.084.32891323.314.45455--1219202.57-7634682.47-31662083.865.42415002.081725502.14-1418561.64-2826881.86-3634842.01550601.97-024712.16-16746371.67-229840.95-18037404521731.74-40028501.75514542.00-039591.59-14317001.85-a.Expressedas96ofweevilledlayer2pine(characterizedbyaverageheightanddbhvalues).b.Meetallrequirementsofawallspacedtreewiththeexceptionofweevildamage(i.e.goodformandspacing).c.n=3trees.26HSx HCw PIH CwB HCw HPI HB16 16 16 13 16 16 16 10 13 108 7137 6126 6 5 6 6 5 5 5 5 9 5 5 5 6 6Spotburn Spotburn Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Spotbum Scarified Scarified Scarified Scarified Nil Nil Nil Nil Nil NilICHg3.01PISxICHg3PISxlCHg3.01PIHICHg3.08P1ICHg3.01HCwICHg3.01SxHwICHg3.01102!03SxPIICHg3.OlaHBICHg3.01PIAtICHg3.01HPIICHg2.01HSxICHg3.09bSxPllCHg3.01103SxBICHg3.01103PISxlCHg3.01103HlCHg3.01109SxPIICHg3.09PISxICHg2.04HBlCHgS.01102PISxICHg3.01l03SPIICHg3.01!03PIAtICHg3.01SxCwICHg2.01104HSxICHg3.01SB109876z4320Figure 5. Age distribution of pine plantations surveyed for Hylobius warrenidamage, Kispiox Forest District, Hazelton, B.C., Summer 1989.5 6 7 8 9 10 11 12 13 14 15 16PLANTATION AGE273.1.4 Weevil incidence in relation to site and stand factorsThe incidence of root collar weevil damaged trees was greater in older plantations thanyounger plantations (Table 1, Figure 6). The average percent oftrees attacked in plantationsolder than 10 years was 48%, but was only 14% in plantations younger than 10 years. Thepercentage oftrees damaged by Warren’s collar weevil also increased with increasing average treeheight (Figure 7). Average tree height increased with increasing plantation age (Tree height =0.45 xPlantation age -0.51, R2 = 0.91, SE = 0.64, p< 0.05).There was no apparent relationship between the percentage of trees with weevil damageand the total number of stems/ha (sph) (Figure 8). Surveyed plantations ranged from 1054 sph to9132 sph.There was not a good relationship between average LFH layer depth and the percentageof pine with root collar weevil damage (Figure 9). The LFH layer depth varied from 3-15 cm.Burning or scarification did not reduce the abundance of weevils (Table 1). The averagepercentage of trees with larval damage was 55.7% on broadcast burn blocks, 26% on spotburnblocks, 15.8% on scarified blocks and 13% on blocks with no site preparation treatment. Theaverage age of plantations with each treatmenttype was 16 years for broadcast burned blocks, 8years for spotburn blocks, 6 years for no treatment and 5 years for scarified blocks. Two SalmonRiver plantations which were scarified had high levels of weevil damage (Table 1; 93M032-01 1and 93M032-014).28100%90%.80%.70%% OF STEMS ATTACKED = -12.03 + 4.20 x PLANTATION AGE60%R2 = 0.64, SE = 13.37, p<O.OOl50%.z40%• .•.30%‘F0o.z•.zA .10%/.S.$0% I I I I I0 2 4 6 8 10 12 14 16 18 20PLANTATION AGEFigure 6. Percentage of sampled Lodgepole pine with Hylobius warreni damagein relation to plantation age in the Kispiox Forest District, Hazelton,B.C., Summer 1989.29100%90%.80%.70%% OF STEMS ATTACKED = - 4.27 + 8.69 x AVERAGE TREE HEIGHTR2 = 0.61, SE = 14.5, p <0.001uv,,o50°/.. 40%©.30%....20%...10%.II •. S0% I •i I I0 1 2 3 4 5 6 7 8 9 10AVERAGE TREE HEIGHT (m)Figure 7. Percentage of sampled Lodgepole pine with Hylobius warrenidamage in relation to average tree height in the Kispiox ForestDistrict, Hazelton, B.C., Summer 1989.30100%% OF STEMS ATTACKED = 32.75 - 1.83 x 10 x SPH90%R2 = 0.02, SE = 22.64, p > 0.05.80%.70%60%.50%..40%.. .30%...20%....10%.. .• ••0% I0 2000 4000 6000 8000 10000STEMS PER HECTAREFigure 8. Percentage of sampled Lodgepole pine with Hylobius warrenidamage in relation to plantation density in the Kispiox ForestDistrict, Hazelton, B.C., Summer 1989.31100%% OF STEMS ATTACKED = 29.12 -0.37 x AVG. LFH DEPTH90%R2 = 0.002, SE = 22.88, p > 0.0580%.o.70/o‘no,v’J/o.50%..40%o..30%20° 0... .10%.• a..0% I I I0 2 4 6 8 10 12 14 16 18 20AVERAGE LFH DEPTH (cm)Figure 9. Percentage of sampled Lodgepole pine with Hylobius warrenidamage in relation to average organic matter layer depth in theKispiox Forest District, Hazelton, B.C., Summer 1989.32Eighty-seven percent of sampled plantations were within the ICHg3 subzone. Of these87%, 85% were within the ICHg3.01 ecosystem association. One hundred percent of plantationssurveyed were within the ICHmc3 biogeoclimatic variant. There was a wide range ofweevilincidence within all sampled plantations irrespective of ecosystem association. In general, weevildamage was prevalent on circum-mesic well drained sites. Within the Kispiox District thisincludes the ICHg3. 01/03/08/and 09 ecosystem associations. Under the new classificationsystem susceptible site series would include the ICHmc3/0 1/04/05.Plantations on sites which had a pine component prior to harvest, or were adjacent tostanding mature pine, appeared to be most susceptible to weevil damage (Table 1). The averagepercentage of stems with weevil attacks in plantations established on sites which previously had aP1 component in the inventory was 31%; the average for plantations on sites with P1 as a minorcomponent (or no component) in the previous stand was 20%. However, some plantations whichhad minor components of P1 prior to harvest had relatively high rates of weevil damage (Table 1).There was no indication that elevation, slope, or aspect had an impact on weevilabundance. The elevational range of the plantations varied from 300 m to 884 m (average:487 m;S.D. :137 m) (Table 1). The slopes on surveyed plantations ranged from 0-50% (average:15%;S.D. :9.9%).3.1.5 Within plantation distribution.Weevil attack pattern was not stratified within a plantation. Weevil damaged trees wereeither randomly distributed within sampled plantations or the distribution was clumped in noparticular pattern.333.1.6 Within district distribution.Root collar weevil was found in all surveyed plantations within the Kispiox Forest District(Table 1). The Seven Sisters plantation (103P009-O1 1) had a 0 % infestation rate based on oursurvey data; however, weevil damaged trees were found outside of the plot boundaries. Highweevil attack rates were found in all older pine plantations within the district. Plantations withparticularly high levels of infestation were found in the Suslcwa River, Nash Y and Shandilla areasof the district. Salmon River plantations, which were considerably younger, were also heavilyinfested. The upper Kispiox drainage (Sterritt Cr., Ironside Cr., Cullen Cr.) had relatively lowlevels of weevil damage.3.2 Height Growth and Dispersal Study3.2.1 Plot summaries3.2.1.1 Date CreekSeventy percent of all sampled trees had evidence of weevil damage (Table 2). Eighty-onepercent of all sampled lodgepole pine had evidence of attack, while 37% of all sampled spruce hadevidence of attack. All dead pine appeared to have died as a result of weevil feeding as indicatedby root collars which were completely girdled. The total mortality attributed to Warren’s collarweevil was only 3% of sampled trees (Table 2).The average diameter of attacked pine was 7.9 cm (Table 3). The average number oflarvae per tree was 1.2. The number of weevils per hectare, based on the average number ofweevils per tree and the estimated stems per hectare, was 850. The percentage of trees attackedwithin a diameter class increased with increasing diameter class (Figure 10). There was asignificant relationship between root collar diameter and percentage of stem girdled (Figure 11).The regression of percent of stem girdled on LFH depth was also significant (Figure 12).34Table 2. Number and percentage of sample trees attacked by Hylobius warreni, by host species,at Date Creek in the Kispiox Forest District, Summer 1990.Lodgepole pine SpruceAttacked Unattacked Dead Attacked UnattackedTotal Trees 265 66 9 18 49Stems per hectare 663 165 23 45 123% of Species Total 78 19 3 37 63Table 3. Population estimates ofHylobius warreni and characteristics of attacked lodgepole pinetrees at Date Creek in the Kispiox Forest District, Summer 1990.Weevil Numbers per TreeRCDa_______________________________LFII(cm) % GIRDLED 1STYEARC2NDYEARd3RDyEAReTOTAL (cm)AVERAGE 7.9 34 0.5 0.3 0.5 1.2 7S.D. 3.9 33 1.0 0.6 1.0 0.9 4a. Root Collar Diameterb. % ofroot collar circumference girdledc. Larvae hatched from the current years eggs (1990)d. Larvae hatched from 1989 eggs.e. Larvae and pupae from 1988 eggsf. Average depth oforganic layer above mineral soil.357060c,)5040300Z2010030ROOT COLLAR DIAMETER (cm)Figure 10. Diameter distribution of sampled Lodgepole pine trees and proportionattacked by Hylobius warreni at Date Creek in the Kispiox ForestDistrict, Summer 1990.0 5 10 15 20 2536100%80%60%40%20%0% - —— — — — — — I — I I I0 2 4 6 8 10 12 14 16 18 20ROOT COLLAR DIAMETER (cm)Figure 11. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to root collar diameter at Date Creek in the Kispiox Forest District,Summer 1990. (% of stem girdled =11.00 + 3.36 x RCD, R2 = 0.14,SE 30.41,p<0.05)... ..• •••...• .•.••••.••••.••..•• ••••.•.••.••lI••.. i%i•.*••lb..•. I•...•••••..S.••••l••...*n330••••••.•*.37z0%0 2 4 6 8 10 12 14 16 18 20LFH DEPTH (cm). ....•:•. •I•••.•....... ......•••• II.••II ••S••.I.•I100%80%60%40%20%•.I.I•.•1a•1.•I• .%..SII.•I...•i•II••1.11.—I..I...II...••••••S.I.•IS.II• ••• :.%.:II....I.•.I.II•In313I0•Figure 12. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to average organic matter layer depth at Date Creek in the KispioxForest District, Summer 1990. (% of stem girdled = 18.67 + 3.06 x AVGLFH depth, R2 = 0.10, SE = 31.06,p<0.05)383.2.1.2 Mosquito FiatsEighty-four percent of all sampled trees had evidence of weevil feeding (Table 4). Eighty-eight percent of all sampled pine had evidence of weevil damage, while 11% of sampled sprucehad been damaged by root collar weevil feeding. Sixty percent of the dead pine were killed byweevil girdling and 40% were killed by stem infections of western gall rust (Endocronarliumharknessii (J.P.Moore) Y.Hirat). However, total mortality within the plot was only 2% ofsampled stems (Table 4).The average diameter of attacked lodgepole pine was 14.1 cm (Table 5). The averagenumber of weevil larvae per tree was 1.4. The number of weevils per hectare, based on theaverage number of weevils per tree and the estimated stems per hectare, was 1100. Thepercentage of trees attacked within a diameter class increased with increasing diameter class(Figure 13). There was a significant regressions between percentage of the root collar girdled andboth root collar diameter (Figure 14) and LFH depth (Figure 15).The Mosquito Flats plantation had a small outbreak ofa sawfly (Neodiprion nanuluscontortae Ross) (Rod Garbutt Pers. Comm.)4during thesummer of 1990; however, damage wasminor.4Forest Insect and Disease Ranger, Prince Rupert Forest Region39Table 4. Number and percentage of sample trees attacked by Hylobius warreni, by host species,at Mosquito Flats in the Kispiox Forest District, Summer 1990.Lodgepole pine SpruceAttacked Unattacked Dead Attacked UnattackedTotal Trees 235 34 5 1 9Stems per hectare 783 113 17 3 30% of Species Total 86 12 2 11 89Table 5. Population estimates ofHylobius warreni and characteristics of attacked lodgepole pinetrees at Mosquito Flats in the Kispiox Forest District, Summer 1990.Weevil Numbers per TreeRCD’______________________________LFH(cm) %GIRDLEb ISTYEARC 2NDYEARd 3RDyEAReTOTAL (cm)AVERAGE 14.1 60 0.2 0.5 0.7 1.4 7S.D. 4.2 30 0.5 1.0 1.1 0.9 4a. Root Collar Diameterb. % ofroot collar circumference girdledc. Larvae hatched from the current years eggs (1990)d. Larvae hatched from 1989 eggs.e. Larvae and pupae from 1988 eggsf. Average depth oforganic layer above mineral soil.4070605040j)2010ROOT COLLAR DIAMETER (cm)Figure 13. Diameter distribution of sampled Lodgepole pine trees and proportionattacked by Hylobius warreni at Mosquito Flats in the Kispiox ForestDistrict, Summer 1990.00 5 10 15 20 25 3041100%80%c-)z60%40/oj)C20%0%0 5 10 15 20 25 30ROOT COLLAR DIAMETER (cm)Figure 14. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to root collar diameter at Mosquito Flats in the Kispiox ForestDistrict, Summer 1990. (% of stem girdled = 21.10 + 2.27 x RCD,R2= 0.12, SE =30.11,p<0.05). . *,ii• ••••••• . ...... ..S •.••.••.•••••. ••••• I• •••• .$•••••••••••S.••.....•.... %......I..••.I••.I •I•.•_#•4h•• •I•:••I . •II• In=256II42100% •...••.•••• ......Figure 15. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to average organic matter layer depth at Mosquito Flats in theKispiox Forest District, Summer 1990. (% of stem girdled = 38.60 +1.91 x LFH depth, R2 = 0.05, SE = 31.23,p< 0.05).... . ...$...w.. •..••.••. S.•••.•••.•.......•.•I.80%60%40%20%•0%•......I..a...••..•.n=256•0 5 10 15 20 25 30LFH DEPTH (cm)433.2.1.3 ShandillaNinety-two percent of all sampled trees had evidence of weevil feeding (Table 6). Ninety-one percent of all sampled pine had evidence of weevil feeding, while 25 % of sampled sprucewere attacked. Weevil caused mortality was 0.6 %.The average diameter of attacked pine trees was 13.8 cm (Table 7). The average numberof weevil larvae per tree was 2.6. The number ofweevils per hectare, based on the averagenumber ofweevils per tree and the estimated stems per hectare, was 3680. The percentage oftrees attacked within a girdling class increased with increasing diameter class (Figure 16). Therewas a significant regression between the percentage of the stem girdled and both root collardiameter (Figure 17) and LFH layer depth (Figure 18).3.2.2 Pattern of AttackDestructively sampled trees had been attacked within the last 5-6 years (Tables 8-10).The earliest attacks on trees in Date Creek and Mosquito Flats occurred in 1984, while theearliest attacks in Shandilla occurred in 1987. The majority of attacked trees had both old andnew attacks.The time of weevil attack was uniform throughout the plots (Tables 8-10). Trees at theperiphery of the plot were attacked during the same years as those within the interior of the plot.The proportion of trees attacked within a basal area class increased with increasing basalarea for all three surveyed plantations (Figure 19).3.2.3 Stem Analysis3.2.3.1 Date CreekRoot collar diameter (RCD) and diameter at breast height (DBH) were significantlygreater in the attacked girdling classes than in the unattacked girdling class (Table 11). Averagetree height in all three damaged girdling classes was greater than the average total height ofunattacked trees (Figure 20). Annual height increment in the 1-50 % girdling class during 198944Table 6. Number and percentage of sample trees attacked by Hylobius warreni, by host species,at Shandilla in the Kispiox Forest District, Summer 1990.Lodgepole pine SpruceAttacked Unattacked Dead Attacked UnattackedTotal Trees 424 35 3 1 3Stems per hectare 1413 117 10 3 10% of Species Total 92 7.5 0.5 33 67Table 7. Population estimates ofHylobius warreni and characteristics of attacked lodgepole pinetrees at Shandilla in the Kispiox Forest District, Summer 1990.Weevil Numbers per TreeRCD______________________________LFI1(cm) %GIRDLEb1STYEARC2NDYEARd3) TOTAL (cm)AVERAGE 13.8 60 0.2 0.6 1.8 2.6 9S.D. 3.2 30 0.5 0.8 2.7 1.3 4a. Root Collar Diameterb. % ofroot collar circumference girdledc. Larvae hatched from the cuerent years eggs (1990)d. Larvae hatched from 1989 eggs.e. Larvae and pupae from 1988 eggsf. Average depth of organic layer above mineral soil.45160990/C HEALTHY TREES140ATI’ACKED TREES100%12010095%8006040z21% 83%100%r100%200% 100%00510 15 2025 30ROOT COLLAR DIAMETER (cm)Figure 16. Diameter distribution of sampled Lodgepole pine trees and proportionattacked by Hylobius warreni at Shandilla in the Kispiox ForestDistrict, Summer 1990.46100% . . . —••.80%z60%40%20%0% -0 5 10 15 20 25ROOT COLLAR DIAMETER (cm)Figure 17. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to root collar diameter at Shandilla in the Kispiox Forest District,Summer 1990. (% of stem girdled = 13.44 + 2.99 x RCD, R2 = 0.15,SE = 28.76,p<0.05)....S.•...........%....• .•,•.S..•.•II•.IIIIn=459III•I•I• I.“v.•••.• I.•,I..I•I•I.I•IIIa aa a47100%80/az60%10j) 40/o020%0%0 5 10 15 20 25LFH DEPTH (cm)Figure 18. Percentage of sampled Lodgepole pine with Hylobius warreni damage inrelation to average organic matter layer depth at Shandilla in the KispioxForest District, Summer 1990. (% of stem girdled = 24.71 + 3.32 x LFH,R2= 0.15, SE = 28.83,p<0.05).. .* ... ..•. ••*.:: .••. •••• •..•• ••.:•••• :.‘;;: • ••?:•;:•.•••. •..:.•••• 0•/•••••.•,••.••I•I•••a.:1.••.I••.- .0••.•.••.I.•0•*11•••.•• ••.••.•:•.1.•n=459••.-9--•.48Table 8. Timing of attack ofHylobius warreni on sample trees in a 13 year old lodgepole pineplantation at Date Creek in the Kispiox Forest District, Summer 1990.Tree # %Girdleda RCDb(cm)Year(s) of Attack44 0 11.5 Nil206 0 10.2 Nil239 0 9.3 Nil318 0 9.5 Nil341 0 10.3 Nil376 16 18.0 1987-198996 20 16.3 1986-1989287 20 15.1 1987-1989345 30 15.5 1987-198970 47 13.2 1985-1989212 53 14.4 1987-1989216 53 14.2 1987-1989371 61 16.0 1985-1989207 62 16.5 1984-1989139 66 13.2 1985-198998 72 15.2 1985-1989178 75 18.0 1986-1989389 84 16.3 1984-1989221 89 15.0 1984-1989277 99 14.0 1987-1989a. % ofroot collar circumference girdled.b. Root Collar Diameter49Table 9. Timing of attack ofHylobius warreni on sample trees in a 17 year old lodgepole pineplantation at Mosquito Flats in the Kispiox Forest District, Summer 1990.Tree # % Gird1ed’RCDb(cm)Year(s) of Attack83 0 12.6 Nil107 0 10.9 Nil160 0 10.6 Nil179 0 20.4 Nil20 8 20.5 1987-1988198 17 21.1 1987-1989273 18 20.2 1987-198939 22 19.5 1987-1989182 48 20.6 1988-1989254 57 20.9 1987-198948 62 23.3 1984-1989281 63 21.5 1988-1989284 65 21.8 1987-198944 69 21.6 1987-198932 82 18.2 1987-1989127 84 17.7 1986-1989277 85 21.2 1985-1989280 85 20.2 1985-198946 98 22.4 1987-1989a. % ofroot collar circumference girdled.b. Root Collar Diameter.50Table 10. Timing of attack ofHylobius warreni on sampled trees in a 17 year old lodgepole pineplantation at Shandilla in the Kispiox Forest District, Summer 1990.Tree # %Girdleda RCDb(cm)Year(s) of Attack510 0 10.2 Nil531 0 11.6 Nil547 0 14.2 Nil626 0 11.1 Nil966 0 12.0 Nil612 8 19.2 1989591 21 17.6 Pre-1987880 21 18.4 1987-1989549 38 14.9 1987-1989668 38 20.1 1987-1989876 51 21.4 1988-1989921 55 20.6 1987-1989877 63 19.9 1987-1989743 79 19.6 1987-1989862 79 19.6 1987-1989871 84 20.2 1987-1989771 89 18.9 1987-1989673 94 20.4 1986-1989889 98 20.2 1987-1989727 99 19.8 1987-1989a. % ofroot collar circumference girdled.b. Root Collar Diameter.51c-)(I)I100%80%60%40%20%0%0 5 20 44 79 123 177 241 314 398 491 594 707TREE BASAL AREA CLASS (cm2)Figure 19. Percentage of sample lodgepole pine with Hylobius warreni damage inrelation to basal area class for three plantations in the Kispiox ForestDistrict, Summer 1990.52Table11.StemanalysisoflodgepolepinetreesattackedbyHylobiuswarreniatDateCreekintheKispioxForestDistrict,Summer1990.AverageInternodeLengthGirdle’RCD2DBH3Class(cm)(cm)19801981198219831984198519861987198819890%1O.2a47.7a27.4a37.4a47.2a54.2a60.Oa49.8a48.8a47.2a44.Oa55.6ab1-50%16.2b11.3b47.Oa45.2a59.8a54.2a59.6a62.2a51.8a49.8a42.4a72.Ob51-70%14.91,1O.7b49.6a48.Oa62.8a61.4a60.4a57.6a59.Oa57.8a49.2a49.2a71-99%15.7b11.2b47.2a54.6a44.2a46.8a66.6a69.2a59.2a45.2a45.6a42.6a1.%ofrootcollarcircumferencegirdled2.RootCollarDiameter3.DiameteratBreastHeight4.Meansfollowedbythesameletternotsignificantlydifferent(SNK;P<O.05)531000400100Figure 19. Cumulative average tree height of lodgepole pine, in four Hylobiuswarreni girdling classes, at Date Creek in the Kispiox ForestDistrict, Summer 1990.90080070060050030020001976 1978 1980 1982 1984 1986 1988YEAR54was significantly greater than the height increment in all other girdling classes (Table 11).However, there were no significant differences in annual height increments between the girdlingclasses in any other year.3.2.3.2 Mosquito FlatsRoot collar diameters were significantly greater in all attacked girdling classes than in theunattacked girdling class (Table 12). The 1-50 % and 5 1-80 % girdling classes had significantlylarger DBIfs than did the unattacked girdling class. Average tree height was greater in all threedamaged classes than in the unattacked girdling class (Figure 21). Height increment wassignificantly larger for attacked trees in all girdling classes in 1979 when compared withunattacked trees (Table 12). There were also significant differences between unattacked trees andtrees in both the 51-80 % and 81-99 % girdling classes in 1980. However, unattacked trees hadshorter height increments in both years.3.2.3.3 ShandillaRoot collar diameters were significantly larger in all attacked girdling classes whencompared with the unattacked class (Table 13). The 1-50 % girdling class had significantlysmaller RCD’s than did the 51-80 % and 81-99 % girdling classes. Unattacked trees hadsignificantly smaller DBHs than did attacked trees, while trees in the 1-50 % girdling class hadsignificantly smaller DBH’s than those in the 51-80 % girdling class. The average heights ofattacked trees in all three girdling classes were taller than trees in the 0% girdling class (Figure22). Unattacked trees had significantly shorter height increments than those in the 5 1-80%girdling class during 1979 and 1980 (Table 13). Unattacked trees had significantly shorterincrements than trees in all other girdling classes in 1984. Height increments were significantlygreater in the 1-50 % class than in the 5 1-80 % class during 1989.55Table12.StemanalysisoflodgepolepinetreesattackedbyHylobiuswarreniatMosquitoFlatsintheKispioxForestDistrict,Summer1990.AverageInternodeLength(cm)Girdle1RCD2DBH3Class(cm)(cm)197919801981198219831984198519861987198819890%13.6a41O.2a18.5a27.8a29.8a61.Oa53.8a61.Oa61.3a50.8a48.Oa44.3a55.5a1-50%20.4b13.5b50.8b45.8ab63.Oa54.6a58.2a61.2a59.4a65.4a52.Oa52.4a52.2a51-80%21.8b14.2b61.8b52.8b50.8a57.8a51.8a47.2a39.2a45.Oa45.8a51.8a39.8a81-99%19.9b12.5ab57.2b55.6b46.4a59.8a51.6a70.4a38.8a51.8a47.8a43.8a39.8a1.%ofrootcollarcircumferencegirdled2.RootCollarDiameter3.DiameteratBreastHeight4.Meansfollowedbythesameletternotsignificantlydifferent(SNK;P<O.05)561000400300200100YEARFigure 21. Cumulative average tree height of lodgepole pine, in four Hylobius warrenigirdling classes, at Mosquito Flats in the Kispiox Forest District, Summer1990.90080070060050001973 1975 1977 1979 1981 1983 1985 1987 198957Table13.StemanalysisoflodgepolepinetreesattackedbyHylobiuswarreniatShandillaintheKispioxForestDistrict,Summer1990.AverageInternodeLength(cm)Girdle1RCD2DBH3Class(cm)(cm)197919801981198219831984198519861987198819890%11.8a48.7a1-50%18.Ob12.6b51-80%20.2c15.lc81-99%19.9c13.Sbc37.Oa40.6a41.4a49.8a51.Oa56.2a52.4a49.Oa58.6a44.3a52.Oa44.8ab51.Oab48.6a53.6a68.8a71.4b67.8a52.6a49.2a56.6a60.Ob55.4b61.4b64.8a71.Ob70.6a74.8b64.Oa56.4a55.8a55.4a38.4a46.Oab56.4ab62.8a67.4b66.Oa76.8b56.8a62.4a57.Oa50.2a52.Oab1.%ofrootcollarcircumferencegirdled2.RootCollarDiameter3.DiameteratBreastHeight4.Meansfollowedbythesameletternotsignificantlydifferent(SNK;P<Z0.05)5810004003002001001975 1977 1979 1981 1983 1985 1987 1989Figure 22. Cumulative average tree height of lodgepole pine, in fourHylobius warreni girdling classes, at Shandilla in the KispioxForest District, Summer 1990.90080070060050001973YEAR594.0 DISCUSSION4.1 Distribution and Abundance of Warren’s Collar WeevilThe 3.99 m radius circular plot was chosen for the district wide survey for a number ofreasons. First, circular plots were easier to establish than were strip plots. One person could putin a circular plot, whereas two people would be needed to establish a strip plot, thus requiringtwice the time. Ease of establishment was important for the following reasons. In order to fi.iffillthe goal of surveying 30 plantations in a 16 week period, it was necessary to optimize labourresources. The circular plot enabled almost twice the area to be surveyed with the same sizecrew. Also, if the survey was to be cost effective in the long run (i.e. could be integrated into thepresent Ministry of Forests silviculture surveys format), it was advantageous to have a methodthat could be implemented by a crew of one. This would keep survey costs at a reasonable level.Second, circular plots are commonly used in other silviculture assessments such asregeneration and free-growing surveys. The data required to assess Warren’s collar weevilabundance could be easily collected at the same timeas a free-growing survey. The surveymethod was quite effective in assessing weevil damage. In only one case, the Seven-Sistersplantation in the SW region of the district, did the plots failto contain trees with weevil larvaldamage when there was evidence of it within the plantation.Third, the time required to establish a circular plot was generally less than the time neededto put in strip plots (this was dependent on tree density). For strip plots,data gathering was acontinuous process, whereas in circular plots, more time wasspent travelling between plots.60Fourth, circular plots could be distributed more evenly throughout a plantation than stripplots. Because of the continuous nature of strip plots, the minimum coverage within a givenhectare was 2% of the area. To achieve the desired sampling intensity of 1% of the area for thestudy, it would not be possible to survey every hectare within a plantation using the strip plotmethod. The circular plot ensured that there were at least two plots per hectare (or 1 plot/ha fora 0.5 % intensity survey). Weevil populations are contagious in distribution (Cerezke 1969), thusthe circular plot survey may be more usefhl for detecting weevil attacked trees, since it coversmore ground than does the strip survey.The lesser perimeter of the circular plot (25 m vs 54 m for strip plots) resulted in fewerjudgement calls ofwhether a tree was in or out of the plot. This minimized potential errorassociated with judgement calls. It also reduced the time spent determining if a tree was within aplot or outside of it.The surveyed plantations were well distributed within the district, and provided a goodoverview of the distribution of Warren’s collar weevil. The wide range of ages of plantationssurveyed provided some insight into the expected levels of Warren’s collar weevil in thedevelopment of plantations to the free-growing stage. For example, based on this survey, a 6 yearold stand with 5 % weevil incidence might be expected to have a 45 % weevil incidence by age 15years. Plantations within a given drainage were of similar ages. For example, plantations in theUpper Kispiox River were relatively young (5-7 years), while plantations in the Suskwa Riverdrainage were among the oldest in the district (10-16 years).The average percentage of sampled lodgepole pine with larval damage was found to begreater in the Kispiox Forest District than values reported in Alberta. Near Robb, Alberta,Cerezke (1969) reported attack rates ofbetween 2.8% - 13.7% for 2.8 m -3.2 m tall lodgepolepine.61The average number of weevils per tree was greater than those previously reported forsimilar stands. Cerezke (1970c) found between 0.03 and 0.13 weevils per tree in 15 and 20 yearold stands in Alberta. This was considerably less than the 0.33 weevils per tree found in thisstudy. The higher weevils per tree found in this study may have been a result of differences instand density and not population levels. In Alberta, Cerezke’s studies were done in naturallodgepole pine stands where tree densities were quite high(> 2500 sph). This study concentratedon pine plantations in which planting densities were generally in the range of 1100 -1300 sph.Thus, in plantations, weevil numbers per tree may be greater than would be found in naturallyregenerated pine plantations.The average mortality rates attributed to Warren’s collar weevil larval damage were withinlevels reported by Cerezke (1969). Some young plantations within the district had high levels oflarval caused mortality. In particular, two 5 year old plantations in the Salmon River area hadhigh mortality levels (6% and 8.8%). These plantations were established on a flat bench adjacentto the Salmon River. The high mortality levels may have been a result of the harvesting pattern inthis area. The original stands were dominated by mature lodgepole pine which was attacked bymountain pine beetle (Dendroctonusponderosae Hopkins). These stands were salvage harvestedand planted to lodgepole pine the following year. Residual mature lodgepole pine within the areaexhibited evidence of root collar weevil. The weevil populations in the clearcut areas immediatelyfollowing harvesting (i.e., the first two years post-harvest) would have increased due to decreaseddevelopment times in the cut stumps (Cerezke 1973b). These weevils would have dispersed fromthe clearcut areas to find any available suitable host. In this case, they attacked residual pineadjacent to clearcut areas. These adjacent areas were subsequently logged (i.e. 3 and 4 yearsfollowing the harvest of the surveyed plantations), further decreasing the pine component in thearea. Weevil populations in these blocks following harvest would also have increased; however,62the residual populations would have had few places to inhabit because of the continued removalof the pine type. Because of a lack of larger, more suitable pine trees in the area, adult weevilswould have then invaded the original pine plantations, which were then 4 or 5 years old. The highlevels of mortality would have been a result of both the high weevil populations and the small sizeof the host.The free-growing status of surveyed plantations was being affected by root collar weevil.By definition, a free-growing, or acceptable well-spaced stem, must be free of insect damage.The survey indicated that potential well-spaced stems were being attacked by root weevil. Theeffect that this insect will have over the duration of the stand is not known. Mortality rarelyoccurs in attacked trees older than 30 years (Cerezke 1969). Perhaps free-growing assessmentsshould be delayed in plantations known to support weevil infestations to ensure that the weevil isnot preventing free-growing standards from being achieved. Another alternative would be toschedule reconnaissance surveys in plantations between 20 and 30 years old to assess the healthand stocking of stands which have been declared free-growing.In the Kispiox Forest District, it can be expected that the percentage of trees attacked byroot collar weevil will increase as stand age and average tree height within plantations increase.This will occur for two reasons: increasing suitability of the host trees, and relatively constantstand densities. The population ofweevils within naturally regenerated stands is constant over thelife of that stand (Cerezke 1 970a). As the stand ages, natural thinning processes reduce treedensities. Those trees that remain will be the larger, more dominant trees which are better able tocompete for light and available resources. It is this group of trees which is most susceptible toattack by Warren’s collar weevil. In plantations, trees are planted at target harvest densities, sonatural mortality is much lower than in natural stands. Therefore, the percentage of stems63attacked in plantations will increase much more rapidly than in natural stands since the number ofstems are already at culmination densities. In addition, diameter growth will be greater inplantations because resources are not being lost to trees that would be naturally thinned out.Thus planted trees may provide better weevil habitat at a younger age than naturally regeneratedtrees.The probability of a tree being attacked was related to its basal area. The proportion oftrees attacked within a basal area class increased with increasing basal area. This may be relatedto the nutritional quality of the host tree. The suitability ofthe phloem as a nutritional source forlarvae may increase with increasing tree size. It has also been suggested (G. Weetman pers.comm.) that the incidence of the weevil may be related to crown closure. The ability of a stand tosupport a weevil infestation may increase as it approaches 100% crown closure. The understoreyshading associated with crown closure may be a critical factor in weevil survival.There was no apparent relationship between the percentage of trees with Warren’s collarweevil damage and the total number of stems/ha (Figure 5). Cerezke (1970c) reported evidencethat excessively stocked stands provided poor weevil habitat. None of the plantations surveyedwere excessively stocked with dominant/co-dominant pine, as is found in some natural stands.Therefore, I would not expect tree density to have a large effect on the percentage of treesattacked. Some surveyed plantations had higher tree densities(>2500 sph). These werecomposed of two tree layers. Trees that had seeded in naturally since planting (layer 1 trees)were generally smaller trees and germinants. It was this layer that resulted in the high densitiesrecorded. Planted trees (layer 2 trees) were larger and at lower densities(—-1200 sph). Thesetrees had the most influence on stand conditions, and they better reflect the conditions that mayaffect the susceptibility of that stand to support weevil populations.5Professor, Faculty of Forestry, The University of BritishColumbia64The depth of the LFH layer did not appear to be important in determining if trees wereattacked in either study year. Cerezke (1970c) found that the duff depth (LFH) gave an indicationof the quality of habitat, with the thicker, moister duff depths being the most suitable for larvalsurvival. The method used to measure LFH depths in the first year of the study did not measureduff depth directly at the tree base. It was thought that this may have been the reason why a goodrelationship was not found. During the second year of the study, measurements of the LFH weremade directly at the tree base. Measuring the LFH depth in this manner did show a significantrelationship between the percent of the stem circumference girdled and the LFH depth. Althoughsignificant the equations accounted for only a small portion of the variation in circumferencegirdled at all three study sites. A more important factor to consider when assessing weevil habitatmay be the quality of the LFH layer. Cerezke (1969) found that there were similarities in the LFHlayer at the base of attacked trees. He found that sites witha mixture of a moss and herb layerover the LFH layer were common in attacked trees. This wasalso the case in the Kispiox district.Those sites with a mixture of herbs and mosses anda moist LFH layer had higher attackincidences. The presence of slash and small logsat the base of trees was also common in attackedtrees. Presumably, this woody debris provides moisture andprotection for developing larvae.Pine plantations on circum-mesic, well-drained sites willbe susceptible to infestation byWarren’s collar weevil. Generally, these are the moreproductive sites for growing lodgepolepine. Proposed openings on such sites should be examinedcarefully at the pre-harvestprescription phase to assess the probability that weevils willaffect the next stand. Suitableprescriptions can then be developed to limit the impact ofWarren’s collar weevil over the nextrotation. The presence of pine adjacentto a plantation is important in determining itssusceptibility to root collar weevil infestation (Cerezke1989). The adjacent pine serves as areservoir for root collar weevil populations.65Surveyed plantations which were site prepared either with burning or with scarification didnot have lower percentages of weevil attacked trees than those plantations with no sitepreparation. In fact, openings which had a site preparation treatment had higher percentages ofweevil attacked trees than those that did not. Site preparation is thought to reduce weevilsurvival by reducing the LFH layer, which is important to adult weevil survival (Cerezke 1973b,1989). The benefits of site preparation may be being masked by the age of the plantationssurveyed and the harvest scheduling. The average age for broadcast burned blocks was 16 years,8 years for spotburn blocks, 6 years for no treatment, and 5 years for scarified blocks. Perhapsenough time had elapsed to allow for sufficient build-up of organic material in the burned blocksto support weevil re-invasion. Of the scarified blocks, only two had high weevil incidence. Thesewere found in the Salmon River area, discussed above. The change in forest structure as a resultof mountain pine beetle salvage may be more responsible for the high weevil populations than thefailure of scarification to reduce the LFH layer. Site preparation may be an effective tool indelaying the onset of infestations. This may include broadcast burning and scarification.664.2 Height Growth and Dispersal StudyWith the exception ofthe Shandilla plantation, weevil populations found in the three studyareas were consistent with those previously reported (Cerezke 1 970c). In Alberta, weevilnumbers per hectare in 15-20 year old stands were in the range of 375 to 920. The populations atDate Creek and Mosquito Flats were 850 weevils/ha and 1100 weevils/ha, respectively.Populations at Shandilla were considerably higher, with almost 3700 weevils/ha. The reason forthe high populations may have been related to the original stand composition and the surroundingforest cover. The original stand was composed of approximately 15 -20 % lodgepole pine. Theleading species on the site were hemlock and spruce. The surrounding forest cover consisted ofmixed species stands dominated by western hemlock. The pine component in the area wasnegligible. The existing stand was an island of pine within a hemlock dominated forest. Afterharvesting of the original block, weevils may have dispersed to surrounding residual pine, andmaintained the population until the planted pine was of susceptible size. The population thenincreased as a result of an increase in their preferred host. Dispersal from the pine plantationwould be limited by the lack of lodgepole pine at the plantation periphery. When searching forhosts, adult weevils would be more successful if they remained within the plantation. This likelycontributed to very high population levels within the Shandilla plantation.There was a significant relationship between the root collar diameter of attacked trees andthe percentage of the stem circumference girdled in all three sampled plantations. Although therelationship was significant the equation accounted for onlya small portion of the variability in thepercent of the root collar circumference girdled. The percent ofthe stem girdled increased with67increasing root collar diameter; however, the usefi.ilness of this relationship is limited by the lowR2 value associated with it.The destructively sampled trees in this study had been attacked within the previous 5-6years. This would imply that weevil populations may have increased dramatically within theprevious five years. For instance, 92% of all lodgepole pine at Shandilla had been attacked withinthe previous four years. Likewise, 81 % and 87 % of lodgepole pine trees at Date Creek andMosquito Flats respectively, had been attacked within the previous six to seven years. Theseattack rates were much greater than those reported in Alberta. Cerezke (1969) estimated that 10- 30 % of the trees in 16-25 year old natural pine stands had evidence ofweevil attack. Also,attack levels of greater than 90 % of a stand did not occur until they were at least 60 years old.His studies were done in natural stands in which high initial tree densities occurred. These standswill gradually thin by natural mortality, thus the increase in the percentage of trees attacked withrelation to stand age is partially an artifact of decreasing stand density. In north central BritishColumbia, however, where plantations are planted at or near target densities, there is relativelylittle change in tree density during the life of the stand. Additionally, there are relatively few treesfor weevils to attack compared to natural pine stands of similar age.The high incidence of root weevils within the Kispiox Forest District in general, may be aresult of the conversion of natural mixed species stands to pine plantations. The short period overwhich the natural pine stands within the district were harvested could also have contributedto thecurrent high population levels. Weevil populations were likely present as small endemicinfestations in natural stands prior to these stands being convertedto managed forests. Relianceon lodgepole pine for regenerating circum-mesic sites within the district has resulted ina largeincrease in available weevil habitat. Contributing to this increasewas the removal of much of themature pine during mountain pine beetle salvage operations. Removing the majority of pine in68certain areas, the Salmon River area for example, forced the weevil to disperse into young pineplantations. Had remnant pine stands been harvested over a longer time period, the populationpressure within young plantations may have been reduced.The time of weevil attack found on destructively sampled trees was uniform throughoutthe plots. Trees within the interior of the plot were attacked during the same time period as thosetrees at the periphery of the plot located at the stand margin. Cerezke (1969) estimated thatweevil dispersal rate from the stand margin into naturally regenerated stands would be 10-15 mper year. To support this, destructively sampled trees at the stand periphery should indicateyounger ages of attack than those sampled toward the interior of the plantation. This was not thecase for the Kispiox. Weevils may be capable of longer distance dispersal than previouslythought. Another possibility is that weevils remain in the clearcut and do not disperse tosurrounding mature trees. Weevil larvae may complete development in cut stumps and theresultant adults could survive for up to four years. During this time, the adults would feed onresidual conifer species until trees reached a size suitable for females to oviposit. Since it requirestwo years for newly hatched larvae to complete development within the cut stumps (Cerezke1973b), the time from development of an adult to the time of its death would be six years afterharvest. Thus planted trees within the cutblock would just be susceptible to attack prior to thefourth year of an adult weevil’s lifespan. The pattern of weevil infestations was not clarified inthis study.Destructive sampling indicated that trees in the attacked girdling classes were significantlygreater in size than were trees in the unattacked girdling class for all three study sites. Thisillustrated the weevil’s preference for the larger dominant and co-dominant trees within a stand(Cerezke 1 970a). Adult weevils oviposit at the root collars of the larger trees, presumablybecause they provide a better food source for the developing larvae. The mechanismby which69adults select the larger trees within the stand is not known. Adults may choose trees based onvisual cues such as stem thickness or tree height. This method of host selection has beendemonstrated for the white pine weevil, Pissodes strobi Peck (VanderSar and Borden 1977).Alternatively, adults may choose trees based on olfactory cues. A related species, Hylobius pales(Herbst), a pest of plantation pines, has been shown to be attracted by a combination ofturpentine and ethanol (Phillips et. at. 1988). Adults of Warren’s collar weevil may respond tothese compounds which are released by host trees. Weevil response may be dependent on therelease rates of these compounds: i.e. larger trees emit larger quantities of such compounds thando smaller trees, thus attracting more weevils.The results from the stem analysis indicated that there were no short-term impacts onlodgepole pine height growth as a result of weevil injury. Previous studies had found that girdlingdamage to the stem or root collar of lodgepole pine may result in growth losses. Cerezke (1 970c)found reductions in height growth in pine damaged by root weevil larvae. Height growth wasreduced by 11.5 % in the second year and 16.4 % in the third year following 50 % of the stemcircumference girdled. In a partial girdling experiment, height growth declined gradually until 60% of the stem was girdled. After 60 % of the stem was girdled, height growth declined rapidly(Cerezke 1974). Sullivan and Sullivan (1986) found that semi-girdling by the snowshoe hare(Lepus americanus Erxleben) significantly reduced height growth in lodgepole pine. Trees lessthan 6.0 cm at d.b.h. were most affected. Sullivan and Vyse (1987) reported conflicting results onthe impact of semi-girdling damage by red squirrels (Tamiasciurus hudsonicus Erxleben) onheight growth of lodgepole pine. Height growth was significantly affected in one stand, but it wasnot affected in another stand. However, they warned that growth impacts may not becomeevident until several years following the damage. Additionally,further feeding damage mayadversely affect already damaged trees and thus increase the probability of future height growth70reductions. This may reflect the situation found in this study. As trees are further damaged bysubsequent weevil attacks, it is likely that growth reductions will occur. The average d.b.h. valuesfor sample trees in this study were between 7.9 cm and 14.1 cm. These values are greater thanthe 6.0 cm values reported by Sullivan and Sullivan (1986). It is possible that the larger trees aremore capable of repairing or overcoming weevil injury, although there was no evidence to indicatethis in this study. Further, this study may not have found significant differences in height growthbecause of the obvious differences between girdled and control trees.The Kispiox Forest District will likely continue to support higher weevil populations thanthose experienced in the past. The reliance on the use of lodgepole pine for reforesting naturalmixed species stands will provide increasing habitat for Warren’s collar weevil. The challenge isto keep populations of this insect at levels which are tolerable from a timber managementperspective. Some management strategies which have been suggested include delaying plantinguntil 2-3 years post-harvest, mixed species planting, planting at higher densities, and sitepreparation (Cerezke 1989). Management regimes which more closely mimic natural stands mayreduce the impact of the weevil. These would include regeneration of mixed species historicallyfound in the region.715.0 CONCLUSIONS1. Warren’s collar weevil is found throughout the Kispiox Forest District.2. Warren’s collar weevil is not reducing plantations to below minimum required stocking levels.Weevil-caused mortality was generally quite low(<5%) with a few exceptions. The free-growing status of lodgepole pine plantations is being affected by Warren’s collar weevil. Thepresence of larvae and/or larval damage to well-spaced trees prevents them from being declaredfree-growing under current Ministry of Forests guidelines.3. This study did not identify specific site factors which could be utilized to predict or identifyareas which have the potential to support Warren’s collar weevil infestations. A combination ofgeneral site conditions can identify potential problem areas. Pine plantations established oncircum-mesic sites which previously had, or were adjacent to, timber types with a pine componentappear to be most susceptible to colonization by Warren’s collar weevil.4. Destructively sampled lodgepole pine trees with Warren’s collar weevil damage have beenattacked over the previous 5 - 6 years. Trees have been attacked more than once during this timeperiod.5. Destructively sampled lodgepole pine trees with Warren’s collar weevil damage were attackedduring the same time period. There was no apparent progression of weevil infestation from thestand margin to the interior of the stand as reported in Alberta.726. Warren’s collar weevil has not yet had an effect on the height growth of attacked lodgepolepine trees. This finding may be confounded by the weevils apparent preference for largerdiameter, dominant and co-dominant trees within a stand.736.0 RECOMMENDATIONS1. Warren’s collar weevil should continue to be monitored in pine plantations within the KispioxForest District. The most suitable means of doing this is through the silviculture surveys systemcurrently in use. The impact of the weevil on a site specific basis should be monitored either inconjunction with stocking surveys or through forest health surveys.2. Warren’s collar weevil should be monitored on a regional and district basis to betterunderstand the impact of the weevil on a forest level basis.3. The acceptability of well-spaced trees with Warren’s collar weevil damage as free-growingstems should be resolved. The high incidence of damage within existing lodgepole pineplantations poses a potential liability to both the Crown and Licencees in the event that attackedstems cannot be declared free-growing.4. The impact of Warren’s collar weevil on the growth of attacked stems should be furtherstudied. Longer term, more tightly controlled studies should be implemented to fi.irther determinethe impact of larval feeding damage on the growth of attacked trees.5. Operational trials that reduce populations of Warren’s collar weevil in infested stands shouldbe implemented in conjunction with harvesting activities. Thebest opportunity to limit damage byWarren’s collar weevil is by limiting their re-invasion into plantations. The best means ofachieving this should be examined.746. Implement a detailed study of post-harvest survival of Warren’s collar weevil in a stand, orstands, with a chronic infestation.75BIBLIOGRAPHYCastellano, A., and M. Marsh. 1989. Control of the bark feeding weevil (Hylobius abietis) usinga controlled release of the insecticide carbosulfan. Incitec Ltd., Queensland Australia.Promotional publication. 8pp.Cerezke, H.F. 1967. A method for rearing the root weevil Hylobius warreni Wood (Coleoptera:Curculionidae). Can. Entomol. 99:1087-1090.Cerezke, H.F. 1969. The distribution and abundance of the root weevil, Hylobius warreniWood, in relation to pine stand conditions in Alberta. Ph.D. thesis, University of BritishColumbia, xvii + 221pp.Cerezke, H.F. 1970a. A method for estimating abundance of the weevil, Hylobius warreniWood, and its damage in lodgepole pine stands. For. Chron. 46:392-396.Cerezke, H.F. 1970b. Survey report of the weevil, Hylobius warreni Wood, in the foothills ofAlberta. Can. For. Serv., For. Res. Lab., Edmonton, AB. Tnt. Rep. A-38. 40pp.Cerezke, H.F. 1970c. Biology and control of Warren’s collar weevil, Hylobius warreni Wood, inAlberta. Can. For. Serv., For. Res. Lab., Edmonton, AB. Tnt. Rep. A-27. 28pp.Cerezke, H.F. 1972. Effects of weevil feeding on resin duct density and radial increment inlodgepole pine. Can. J. For. Res. 2:11-15.Cerezke, H.F. 1973 a. Bark thickness and bark resin cavities on young lodgepole pine in relationto Hylobius warreni Wood (Coleoptera: Curculionidae). Can. 3. For. Res. 3:599-601.Cerezke, H.F. 1973b. Survival of the weevil, Hylobius warreniWood, in lodgepole pine stumps.Can. J. For. Res. 3:367-372.Cerezke, H.F. 1974. Effects of partial girdling on growth in lodgepole pine with application tothe weevil Hylobius warreni Wood. Can. 3. For. Res. 4:312-320.Cerezke, H.F. 1989. Proceedings of root collar weevil meeting, August 1989, Hazelton, B.C.B.C. Ministry of Forests, Prince Rupert Forest Region, Memorandum. 14pp.Coulson, R.N., and J.A. Witter. 1984. Forest Entomology.Wiley-Interscience. New York.669pp.Duncan, R.W. 1986. Terminal and root-collar weevils of lodgepole pine in British Columbia.Can. For. Serv., Pac. For. Ctr., For. Pest Leaflet 73. 6pp.Finnegan, R.J. 1961. A field key to the North American species ofHylobius (Curculionidae).Can. Entomol. 93:501-502.76VanderSar, T.J.D., and J.H. Borden. 1977. Visual orientation ofPissodes strobi Peck(Coleoptera:Curculionidae) in relation to host selection behaviour. Can. J. Zool. 55:2042-2049.Warner, R.E. 1966. A review of the Hylobius ofNorth America with a new species injurious toslash pine (Coleoptera: Curculionidae). The Coleopterists’ Bull. 20:65-81.Warren, G.L. 1956a. Root injury to conifers in Canada by species ofHylobius and Hypomolyx(Coleoptera: Curculionidae). For. Chron. 32:7-10.Warren, G.L. 1956b. The effect of some site factors on the abundance ofHypomolyxpiceus(Coleoptera: Curculionidae). Ecology. 37:132-139.Warren, G.L. 1956c. ph and the incidence of attack ofHypomolyxpiceus (DeG.). Can. Dept.Agric., Sci. Ser., For. Biol. Div., Bi-Monthly Prog. Rep. 12:2-3Warren, G.L. 1958. A method of rearing bark and cambium-feeding beetles with particularreference to Hylobius warreni Wood (Coleoptera: Curculionidae) Can. Entomol. 90:425-428.Warren, G.L. 1960. External anatomy of the adult ofHylobius warreni Wood (Coleoptera:Curculiomdae) and comparison with H. pinicola (Couper). Can. Entomol. 92:321-341.Warren, G.L., and R.D. Whitney. 1951. Spruce root borer (Hypomolyx sp.), root wounds, androot diseases of white spruce. Can. Dept. Agric., Sci. Ser., For. Biol. Div., Bi-MonthlyProg. Rep. 7:2-3Whitney, R.D. 1952. Relationship between entry of root-rotting fungi and root wounding byHypomolyx and other factors in white spruce. Can. Dept. Agric., Sci. Ser., For. Biol. Div.,Bi-Monthly Prog. Rep. 8:2Whitney, R.D. 1961. Root wounds and associated root rots of white spruce. For. Chron.37:401-411.Wilson, L.F. 1967. Effects of pruning and ground treatments on populations of the pine rootweevil. J. Econ. Entomol. 60:823-827.Wilson, L.F., C.D. Waddell, and I. Millers. 1966. A wayto distinguish adult Hylobius weevils inthe field. Can. Entomol. 98:1118-1119.Wood, S.L. 1957. The North American allies ofHylobiuspiceus (DeGeer) (Coleoptera:Curculionidãe). Can. Entomol. 89: 37-43.Zar, J.H. 1984. Biostatistical Analysis. 2nd Ed. Prentice-Hall Inc. 718pp.78

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