Can Be Used for Augmentative Biological Control of the Brown Marmorated Stink Bug in Fruit Orchards?

The generalist egg parasitoid (Geoffroy) (Hymenoptera: Eupelmidae) is the most prevalent egg parasitoid of the invasive (Stål) (Hemiptera: Pentatomidae) in Europe. To assess its efficacy against the pest and to validate the potential risks for non-target species in a realistic field setting, inundative releases were conducted over three consecutive years in four fruit orchards in Switzerland and Italy. In total, more than 4300 females were released, which was equivalent to 11,000 to 26,000 females per hectare, depending on distances between trees in each orchard. Parasitism of freeze-killed sentinel eggs achieved with the current release strategy was on average 6% (range: 2%-16%) and considered not high enough to effectively suppress the pest. However, the overall impact of on the mortality of eggs was likely underestimated. If pre-imaginal parasitoid mortality (3.3%) and host feeding (6%) are added to the observed parasitism (6%), the actual induced mortality of eggs may reach more than 15%. Parasitism of lepidopteran non-target species reached an average of 8% and thus, some degree of non-target parasitism after mass releases may be expected. To quantify the impact of the parasitoids in the orchards more precisely, naturally laid egg masses should be used in future trials to include host-finding cues of the host and host plants, and larger scale releases with potentially higher densities of parasitoids should be considered.