Short-range host preference in snowberry maggot flies depends on life history stage

Closely related animal species are often incompletely isolated reproductively and occasionally hybridize. Many host-specific insects are primarily isolated by the reproductive barrier of host choice and provide model systems to study gene flow in sympatry. Understanding conditions that alter barriers like host choice can help us understand reproductive isolation between these species. Hybridization occurs between microsympatric populations of apple and snowberry maggots in Bellingham, Washington which are also not isolated by mating season or assortative mating. I exposed apple and snowberry maggots to their natal fruits in two-way choice experiments to measure their short-range host preferences. I tested snowberry flies at different life stages to determine whether host preference is constant throughout their lives. Virgin flies show no preference for their natal hosts and rarely oviposit. After mating, female snowberry flies strongly prefer their natal host and oviposit solely in snowberries. Young synovigenic females may balance the costs of exploring nearby novel hosts and occasionally mating with heterospecific males with the benefits of finding nutrients to develop their eggs and mates to fertilize them. Mated females will spend most of their time on their natal host where males will follow them. As a result, hybridization between apple and snowberry maggot populations is most likely in the early season before females have mated and started ovipositing in their natal hosts. The fate of evolutionary interactions between species depends on the life history dynamics of the reproductive barriers that isolate them. Future studies should consider strength of reproductive isolation in this context.