Lethal interference competition in the whitefly parasitoids Eretmocerus eremicus and Encarsia sophia.

Recent population-dynamic theory suggests that mechanisms of lethal interference competition can have profound effects on parasitoid coexistence and pest suppression in biological control systems. We investigated lethal intraspecific and interspecific interference competition in Eretmocerus eremicus and Encarsia sophia, parasitoids of the whitefly pest, Bemisia tabaci. Our first experiments evaluated whether one or both species could suppress the progeny production of the other species through two mechanisms of lethal interference competition: (1) usurpation of hosts in cases of multiparasitism, and (2) host feeding on and killing parasitised hosts. We found that both species could suppress the progeny production of the other. E. eremicus' effect on E. sophia appeared to reflect multiparasitism. E. sophia's effect on E. eremicus appeared to reflect a combination of multiparasitism and host feeding on parasitised hosts. Second, we investigated the effects of lethal intraspecific interference on conspecific progeny production in both species. E. sophia interfered intraspecifically by host feeding on parasitised hosts. E. eremicus also apparently host fed on parasitised hosts, however the effect of host feeding on conspecific progeny production was slight. Third, host dissections and behavioral observations confirmed the mechanisms inferred from the progeny production experiments. Our results suggest a need to consider mechanisms of lethal interference competition in theoretical and empirical research on parasitoid competition.