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Ecological factors influencing diapause in the spruce budworm, Choristoneura fumiferana (Clem.). (Tortricidae) Campbell, Douglas Kennedy

Abstract

Investigations were carried out to determine the effect of ecological factors on the induction of diapause in the spruce budworm. Experimental rearings were conducted at elevations of 2500, 4200 and 4750 feet. The foliage of spruce, Douglas fir and alpine fir were used as hosts. Progeny of Ontario, two-year and one-year types reared under one-year and two-year life cycle conditions were used as experimental insects. A trend was observed in emergence from hibernation with the one-year type leading, followed by the two-year and finally the Ontario type. It was shown that the one-year type larvae may adopt the two-year habit. The main factor influencing this is a prolonged development period for the parents. The larvae reared at the higher elevations showed a greater proportion entering diapause. Food played a smaller role with spruce and Douglas fir being more favourable for diapause than alpine fir. The increased percentage of larvae in diapause in 1952 is attributed to a longer development period for their parents and to a sharp drop in temperature occurring about 12 days prior to diapause. The Ontario material may adopt the two-year habit. The factors contributing to this have not been clearly shown as the rearing results are inconclusive. There were no definite differences shown in the time for development among the three foods. The insects at the lowest station developed in approximately three weeks less time than at the highest. The difference between the upper stations was slight. The impracticability of converting a one-year life cycle population to a two-year cycle by forest management is noted. The diapause theories of Wigglesworth and Andrewartha are commented on. A possible course of evolution leading to the establishment of a two-year life cycle population is given.

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