Polyandry across Behavioral Classes in Female Spruce Budworm

Reproduction in spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), is characterized by sedentary oviposition in the natal forest patch early in life (gravid females are incapable of flight due to their heavy abdomen) followed by windborne migrations among females that have laid >50% of their eggs; the nature of migrations (facultative or obligatory) remains unknown. The incidence of polyandry (females with more than one spermatophore in their reproductive tract) was evaluated for several thousand field-collected female budworms (data professionally archived at Canadian Forest Service) using an array of sampling procedures that can be delineated along four behavioral classes: (1) resident females collected on host trees; (2) in-flight females captured while foraging in forest canopies; (3) migrant females captured above tree canopies; and (4) females collected postmortem on drop trays. Overall, polyandry increased over time (reflecting the ageing of local populations) and with female body size (likely due to male mating preference for large, most fecund females). Polyandry did not increase postmortem realized fecundity of females. The level of polyandry was lowest among migrants, intermediate for in-flight and resident females, and highest for naturally dead females. Sedentary reproduction among young female budworms may limit gene flow and increase the risk of inbreeding; a low level of polyandry among migrants may thus be due to females not only seeking novel habitats for their progeny but also mating partners that are not closely related genetically.