Intrinsic competition between larval parasitoids with different degrees of host specificity

1. Interspecific competition among parasitoids may play a key role in the community dynamics of tritrophic plant-herbivore-parasitoid systems and has important implications for management of herbivorous insect pests. 2. A model system was used to explore the outcome of interspecific competition between parasitoids that differ in host specificity. The system included the lepidopteran pest Heliothis virescens, the generalist parasitoid Cotesia marginiventris, and two specialist parasitoids, Microplitis croceipes and Cardiochiles nigriceps. 3. The generalist, C. marginiventris, dominated intrinsic competition when given an 8-h developmental head start over C. nigriceps or when its oviposition was simultaneous with that of M. croceipes. Microplitis croceipes and especially C. nigriceps larvae prevailed when they were allowed to oviposit prior to C. marginiventris. 4. Rates of host mortality prior to parasitoid emergence varied with parasitoid species composition and with the order of oviposition. 5. Implications for integrated pest management and the adaptive significance of competition as related to host specialisation are discussed.