Document: JOH-3-56-33

The community ecology of tachinid-host interactions.

STIREMAN III, J.O.*

University of Arizona, Tucson, AZ 85721 USA ¹

Abstract:
Tachinid flies are a diverse and widespread group of insect parasitoids. Despite their importance as enemies of herbivorous insects in many natural and agricultural ecosystems, their ecological relationships with hosts are largely unknown. Analyses of hymenopteran parasitoid communities and literature databases of parasitoid-host records have revealed a number of factors that influence the richness and character of parasitoid complexes. These include host morphology, host-plant architecture, and host taxonomic affiliation. However, tachinids differ from the better studied hymenopteran parasitoids in a variety of ways that are likely to influence patterns of host use including their avoidance of host immune defenses, their frequent habit of indirect oviposition, and perhaps most importantly, their relatively wide host ranges. These and other traits suggest that ecological characteristics of a host are more important in determining whether it is used by a particular tachinid than its physiology or phylogenetic affinity. In order to examine how ecological characteristics of hosts influence the diversity and identity of tachinids that attack them, I conducted a four year sampling program of diurnal exophytic macrolepidoptera and their parasitoids in the mesquite-oak grasslands of Southeastern Arizona. From this program I have constructed a semi-quantitative parasitoid-host web. Preliminary analyses of these data demonstrated a high variability in local host range among tachinids, with many species being restricted to a single host while others attacked hosts in close accordance with their abundance in the field. In contrast to previous studies, parasitoid species richness was found to be higher on herb-feeding hosts relative to those on trees and higher for hairy caterpillars as opposed to smooth ones. I also found tachinid species richness inversely correlated with the level of host-plant specialization of the host. Host microhabitat, along with certain taxonomically widespread morphological traits, was demonstrated to be of primary importance in determining patterns of host use in tachinids.

Keywords: Parasitoid, Tachinidae, Community Ecology, Lepidoptera, parasitoid-host interactions

This abstract is being presented at: 1:45 PM in session:
Oral Session #15: Parasitoids and Diseases.