Document: CHE-3-51-28

The influence of seasonality on parasitoid coexistence and host abundance.

BRIGGS, C.J.* and J.LATTO

University of California, Berkeley, CA 94720, U. S. A. ¹

Abstract:
Many insects support a rich fauna of parasitoids and predators and competition between these natural enemies is likely to be strong. Here we investigate how seasonality in natural enemy attack influences (a) the potential for coexistence of multiple natural enemy species and (b) the combined impact of these enemies on host abundance. Field experiments have been carried out in Berkeley, California, using a native gall forming midge, Rhopalomyia californica, and its suite of parasitoids and predators. Although the midge has continuous, overlapping, generations there is considerable seasonality within the system. Midge development time can be as short as 40 days in the field but is strongly influenced by the highly variable growth rate of its host plant, Baccharis pilularis. Predation on the egg and early larval stages of the midge was a much higher mortality source on this species than previously appreciated and varied greatly throughout the year. Galls formed at all times of year, but the number of galls formed successfully per female varied seasonally. Development rate of the midge also varied seasonally, as did the relative parasitism of the egg and larval stages which, combined, were as high as 90% of the available hosts. These findings will be combined into a seasonal stage structured model to illustrate how only certain forms of seasonality can promote natural enemy coexistence.

Keywords: host-parasitoid, gall-forming insects, parasitoid competition, seasonality

This abstract is being presented at: 2:45 PM in session:
Oral Session #15: Parasitoids and Diseases.