Influence of intra- and inter-specific competition between egg parasitoids on the effectiveness of biological control of Euschistus heros (Hemiptera: Pentatomidae)

Abstract

Telenomus podisi and Trissolcus basalis are two important parasitoids used as biological control agents against the brown stink bug Euschistus heros. The interaction between these parasitoid species in the field, however, can have different effects on the effectiveness of pest control, depending on the density of the species present and the conditions under which the species find their host's eggs in the field. This study aimed to analyze the effects that may arise when two parasitoid species interact directly or indirectly during foraging at E. heros egg sites. Through experimental scenarios, the effects of intra- and inter-specific competition on unparasitized and previously parasitized host eggs (i.e. simultaneous and sequential parasitism, respectively) on the parasitism rates, emergence rates and emergence patterns were evaluated. For simultaneous parasitism, high emergence rates occurred when T. podisi was the only parasitoid species present in the system. In the presence of T. basalis, the parasitism rates remained high only when T. podisi was also present, although the emergence rate was considerably reduced due to multiparasitism. In sequential parasitism, T. podisi showed higher parasitism rates and offspring emergence due to its greater ability to discriminate eggs previously parasitized by conspecifics. In this scenario, the offspring of the first parasitoid that interacted with host eggs had greater success; however, the larval competition inside the host eggs led to changes in the species emergence patterns as well as to high offspring mortality. Competition changed the emergence pattern of the parasitoid offspring, which can lead to a decoupling of the host-parasitoid dynamics synchrony, by reducing the chances of encounters between the species and consequently the effectiveness of long-term pest control.