Behavioral Ecology of the Walnut Husk Maggot, Rhagoletis Suavis

Annamarie Pasqualone, Vassar College ’10 and Prof. Jeremy Davis

The walnut husk maggot, Rhagoletis suavis, utilizes the black walnut tree (Juglans nigra) throughout the eastern coast of North America as a site for aggregation, female egg-laying, and larval development. While research has been conducted on closely related west coast species (R. juglandis and R. completa), little is known about the conspecific interactions and reproductive decisions of R. suavis. Our work includes an array of analyses on this species designed to determine optimum laboratory conditions for behavioral analysis and seek out promising new research directions.

We have determined that these files are most active between the hours of 7:00-8:00 and 15:00-18:00, which has allowed us to focus our observations on those times when the animals are most likely to be conducting behaviors of interest. Because much of this species’ behavior centers around ripe walnut fruit, we used preference assays to determine the qualities model walnuts must possess in order to effectively serve as an arena for behavioral observations. For example, we found that wooden spheres coated in paint color-matched with ripe walnuts elicited more male territorial behavior than agar spheres dyed with food coloring.

Throughout the course of this study, a number of novel observations were made that may provide future research opportunities. Among these, we found an extreme sex-ratio bias within flies emerging from pupae collected in the fall of 2008 (~2 females:1 male). In addition, several behaviors were exhibited that have not been observed in other walnut infesting species, including a behavior in which males mount mating pairs in an apparent attempt to disrupt copulation events.

Two pilot studies were also conducted that provided promising results. The first suggests that newly emerged females maintained in the presence of mature, egg-bearing females begin developing their own eggs earlier than those maintained in the presence of same-aged females lacking eggs. In a study of male territorial behavior, we found a positive correlation between the proportion of time males spent on the model nut and the frequencies of both mating and intersexual competition, suggesting that males who gain access to the nut have higher mating success. In this study, we also found that male flies display consistent individual differences in both their level of mating effort and in their response to potential predators, suggesting the presence of individual “personalities”. We intend to follow up on these pilot studies over the course of the upcoming academic year.