LARVAL FEEDING-BEHAVIOR AFFECTS THE IMPACT OF STAMINATE FLOWER PRODUCTION ON THE SUITABILITY OF BALSAM FIR TREES FOR SPRUCE BUDWORM

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in con junction with field rearing indicated that the feeding behaviour of th e larvae, which is affected by the insect population density, signific antly influenced the impact of balsam fir, Abies balsamea, staminate f lowering on spruce budworm biology. At low budworm density, the produc tion of pollen in the midcrown of host trees reduced the insect develo pment time by 5 days without affecting pupal weight, fecundity and sur vival. However, at high budworm density, the small amount of current-y ear foliage produced by flowering branches forced old larvae (sixth in star) either to feed on 1-year-old foliage (backfeeding) or to move fr om the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fe d on old foliage, they exhibited reduced pupal weight and fecundity wi thout losing the advange in development time that they obtained from f eeding on pollen during their early stages of development. On the othe r hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in develop ment time that was gained from feeding on pollen. Results from this st udy indicated that the production of staminate flowers by balsam fir t rees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.