Palaearctic Egg Parasitoids Interaction to Three Grapevine Exotic Pests in Northwestern Italy: A New Association Involving Metcalfa pruinosa

The most important exotic leafhopper pests currently affecting the Italian vineyards are the leafhoppers Scaphoideus titanus, Orientus ishidae and the planthopper Metcalfa pruinosa. Their highest population density is detected in the uncultivated areas with wild grapevines. Should these habitats be considered only a problem or a potential resource for Palearctic entomophagy of these three exotic pests? The aim of this work was to study the biotopes and biocoenosis present in the Piedmontese vineyard agroecosystem, evaluating the parasitization rate and other crucial aspects for a possible application in biological control. Several specimens of egg-parasitoid wasps were obtained from filed-collected two-year-old grapevine canes. The most prevalent one belonged to the Oligosita collina group (Trichogrammatidae) emerged only from M. pruinosa eggs with a parasitization rate of over 40%. The new association is the first report of such a high level of parasitization on the flatid planthopper. The parasitization rate mainly relied on the host egg density and the abundance of plants suitable for the oviposition. A second parasitoid generation on the overwintering eggs is discussed, as well as other hypothesis. Furthermore, the parasitization rate was higher than the one showed by the dryinid Neodryinus typhlocybae, the control agent introduced in Italy under the biological control strategy, highlighting a possible implication in this biocoenosis. We assume that the egg parasitoid adaptation may contribute to M. pruinosa control.