Assessing Competitive Interactions in Parasite Guilds Prior to Introduction

Abstract

Analysis of interspecific competition among 3 parasites of an endemic, gall-forming midge ( Rhopalomyia californica Felt) is used to illustrate how competitive interactions in parasite guilds can be assessed prior to introduction in classical biological control. Host galls are multi-chambered and contain either hosts, parasites, or both; galls containing parasites contain either 1, 2, or 3 species of parasites. Parasitization by Torymus koebelei (Huber) and Platygaster sp. was highest when these species occurred alone compared to when they occurred with 1 or 2 other species. Parasitization by Zatropis capitis Burks was the same in single and mixed-species samples. In all cases, total parasitization in mixed-species samples was greater than parasitization in single-species samples. Interspecific copetition occurred among the parasites but did not result in reduced levels of total parasitization. It is suggested that analogous methods can be used to evaluate interspectfic competition among parasites in similar situations.