PARENT SESSION
Oral Session # 89: Insect Ecology II.
Presiding: R Sears
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 101.

Parent-offspring conflict in the walnut fly, Rhagoletis juglandis .

Nufio, Cesar ^{*,1, 2}, Papaj, Daniel², ¹ Natural History Museum, University of Colorado, Boulder, CO² University of Arizona, Tucson, AZ

ABSTRACT- Choosing where offspring will develop is especially important for insects whose larval stages are restricted to a particular host resource. In such insects, maternal egg laying decisions may not only involve choosing optimal hosts based on their intrinsic qualities but also avoiding hosts occupied by conspecific brood. In many insects, the ability to discriminate between previously exploited and unexploited hosts is often mediated by the use of a marking pheromone. Despite engaging in what appears to be host-marking behavior, the walnut fly Rhagoletis juglandis prefers to deposit clutches into previously exploited hosts. In this study, we quantified host reuse in R. juglandis and assessed its impacts on offspring fitness. We also explored the role that marking pheromone plays in determining the level to which hosts are reused. Host reuse by the walnut fly was common in the field, where trees were synchronously infested over a 14 to 17 day period. Field and laboratory experiments showed that increases in larval densities within fruit reduced larval survival and pupal weight, the latter being strongly correlated with the number of eggs a female produced over her lifetime. In field-cage experiments, fruit that were host marked by females for longer durations were less acceptable to other females. Moreover, the duration of time that a female marked a fruit was positively correlated with the size of her clutch. These results indicate that, while females commonly reuse fruit, they nevertheless signal the level of larval competition associated with a fruit and adjust allocation of eggs to fruit accordingly. Host reuse by R. juglandis appears to reflect a strategy by which females attempt to maximize the number of clutches they deposit over a lifetime at the expense of the per capita fitness of her brood.

Key words: Parent-offspring conflict, oviposition decisions, Rhagoletis juglandis, larval competition