Effects of classical biocontrol agents on indigenous natural enemies: reproduction in pomegranate butterfly Deudorix livia eggs by native and imported parasitoids

Abstract

Exotic natural enemies that are imported to control a target pest may attack non-target species or disrupt the performance of other natural enemies of the target that are already present. We evaluate possible interactions between three parasitoid species, the native Telenomus nizwaensis and the imported Trichogramma brassicae and Trichogramma evanescens, when presented with Deudorix livia host eggs under high-density laboratory conditions. Deudorix livia is a butterfly which is an economically damaging pest in the Omani pomegranate agro-ecosystem. Most (73.5% overall) of the observed parasitism was by T. nizwaensis. It performed best when presented with host eggs in the absence of either of the Trichogramma species. These imported species thus have some potential to disrupt suppression of the pest by the indigenous natural enemy under lower-density conditions in the field, and neither of them achieved high parasitism rates themselves (laboratory conditions: T. brassicae = 12.5%; T. evanescens = 18.5%; with no evidence for any parasitism of field-collected eggs). Future efforts in this agro-ecosystem would best be directed towards encouraging T. nizwaensis, rather than towards importation of Trichogramma. Screening for negative effects of natural enemies on the pest suppression provided by other natural enemies is recommended.