The Biological Effects of Venom Derived from the Ectoparasitic Wasp Eulophus pennicornis (Nees) (Hymenoptera: Eulophidae): Evidence for Dual Endocrine Regulation

ABSTRACT

The venom of the ectoparasitoid Eulophus pennicornis is known to induce developmental arrest in parasitized hosts through the prevention of moulting. However, little work has explored how the venom affects different host stages, whether the observed effects vary with different doses, and whether the venom has activity in non-host species. Injections of venom doses of ≥0.5 μg protein prevented the development of > 90% of both fifth and sixth instar Lacanobia oleracea larvae. In fifth instars, developmental arrest at doses of ≥ 1.0 μg occurred prior to ecdysis to the sixth stadium, whilst the 0.5 and 0.25 μg treatments allowed 36% and 77% of injected larvae, respectively, to moult although most subsequently failed to pupate. Although naturally parasitized hosts always showed reduced growth, lower doses of venom often prevented pupation without affecting this parameter, particularly in sixth instar larvae where only the highest dose (2.0 μg) reduced the mean maximum weights achieved. Two factitious lepidopteran hosts, Manduca sexta and Spodoptera littoralis, were also affected by injection of the venom at w/w doses equivalent to those used for L. oleracea although larvallarval moulting was only prevented in the former. Fractionation of venom using gel-filtration FPLC indicated the presence of at least two factors that markedly affected host development. One series of contiguous fractions, on injection, prevented larval-larval ecdysis in a similar way to whole venom. A second series of fractions had no effect on larval-larval ecdysis but resulted in the formation of deformed pupae, an effect that closely resembled the application of a juvenile hormone (JH) analogue, which may indicate the presence of a factor within the venom that modulates host levels of this hormone.