PARENT SESSION
Oral Session #9: Trophic structure and community interactions. Presiding: B. Menge.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.
The effects of parasitoid competition on coexistence and host suppression in a gall-forming midge.
LATTO, JOHN1, BRIGGS, CHERYL1, 1
ABSTRACT- Using a long-term field experiment we are investigating the interaction between two parasitoid species that share a common host. This knowledge will be useful in two related areas: in understanding the mechanisms allowing the co-existence of different species on a common host, and in predicting which combination of parasitoids might best suppress a host insect. In particular, we are testing the prediction that the addition of a larval parasitoid that is superior in larval competition (effectively a facultative hyperparasitoid) but inferior in host searching ability will lead to a disruption of the control of the host achieved by an egg parasitoid acting alone. The field system we are using is the native community of parasitoids on the gall forming midge Rhopalomyia californica that occurs on the shrub Baccharis pilularis in California. Populations of the gall-forming midge have been established on Baccharis plants grown in large enclosures in the field. The experimental treatments consist of: releasing an efficient egg parasitoid; releasing a less efficient larval parasitoid (which is superior in larval competition); releasing neither parasitoid species; or both parasitoid species. We will present the first years experimental data which shows that although the egg parasitoid can reduce the host to a significantly lower density than the larval parasitoid, when they are present together the larval parasitoid does not appear to interfere with the control achieved by the egg parasitoid alone.
KEY WORDS: Rhopalomyia californica, Baccharis pilularis, parasitoid, biological control