Canadian Forest Service Publications
Diapause and voltinism in western and 2-year-cycle spruce budworms (Lepidoptera: tortricidae) and their hybrid progreny. 2005. Nealis, V.G. The Canadian Entomologist 137: 584-597.
Available from: Pacific Forestry Centre
Catalog ID: 25857
Breeding experiments and rearing under variable controlled conditions have revealed that western and 2-year-cycle spruce budworms (Choristoneura occidentalis Freeman and C. biennis Freeman, respectively) from British Columbia, Canada, and their hybrid progeny have the inherent capacity for a variable number of diapause events and hence voltinism. While all crosses have at least one diapause, variability in the relative frequency of a second diapause is determined by genetic traits modified by the photoperiod and, to a lesser extent, temperature experienced during the larval stages. Second diapause appears fixed in C. biennis but is facultative and most frequent at short photophases (12L:12D) in C. occidentalis. Hybrids and backcrosses had responses intermediate to the parental responses under all environmental conditions. The occurrence of a facultative third diapause in all crosses underlines the inherent capacity for flexibility in voltinism in these species. These results are discussed in the context of past, present, and future distributions of alternative life cycles in closely related species.
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