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Rearing studies of the Douglas-fir cone moth, Barbara colfaxiana (Kearfott) (Lepidoptera: Tortricidae)

University of British Columbia

Several attempts were made at improving an artificial rearing method developed by Ruth and Hedlin (1969) for the Douglas-fir cone moth from 1983 to 1985. During 1983 and 1984, different container types, establishment methods and diet formulations were tested resulting in the production of a method that reduced both larval handling and media moisture loss. However, unexpected high mortality occurred during the late L4 stage when the insect constructed a cocoon within or adjacent to the media, and at pupation when developmental problems became obvious. These symptoms suggested the presence of a disease, however, no pathogens were observed with the light microscope. These forms of mortality had not been reported by Ruth and Hedlin (1969). It was postulated that media nutrient degradation was one cause since the method described by Ruth and Hedlin (1969) allowed the larvae to feed continuously on relatively fresh (nutrient rich) media while the larvae fed on unchanged media throughout the larval feeding period with my method. In 1985, two spruce budworm diets (Robertson’s 1981 and Bioserv) were replaced with freshly made media of the same formulation two weeks after establishment with eggs. Although pupal survival differed considerably between the two diets, no significant improvements in larval or pupal survival were obtained by changing media. In a second experiment, the initial concentrations of linolenic and L-ascorbic acid contained in Robertson's (1981) diet were varied to produce 12 different diets. Both nutrients were reported to degrade in artificial diets. Larval survival and pupal production were directly related to the dietary concentration of linolenic but not L-ascorbic acid. The best overall pre-winter survival of 53.9% and post-winter survival of 37.8% were obtained on Roberston's (1981) diet with four times and two times the normal concentration of linolenic acid, respectively. Linolenic acid appeared to be an essential nutrient for the cone moth since its absence produced the worst pre- and post-winter survival. Bioserv -reared pupae and pupae resulting from either of these "best" diets were not significantly different in weight from naturally-reared pupae. Adult emergence success was not affected by increasing quantities of dietary linolenic acid above the normal concentration. The incidence of 2YD appeared related to rearing temperature. Prolonged diapause incidences were significantly different between artificially- and naturally-reared pharate adults for each year of artificial rearing (1983 through 1985). A sample of cone moths from 40 trees revealed that within stand variation of 2YD incidences was relatively narrow. This result suggested that the proportion of cone moths entering 2YD may be regulated by factor(s) that uniformaly affect the stand, such as temperature, rather than as a response to the individual tree's reproductive potential in the year following larval feeding. This relationship and the improvement of the 1985 rearing method requires further investigation.

Text

2010-06-20

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http://hdl.handle.net/2429/25871

Forestry

University of British Columbia

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