Abstract
The generalist egg parasitoid Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) is the most prevalent egg parasitoid of the invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) in Europe. To assess its efficacy against the pest H. halys 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 A. bifasciatus 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 H. halys 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 A. bifasciatus on the mortality of H. halys 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 H. halys 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.
Highlights
Egg Masses (Eggs) parasitoids (e.g., Trichogramma spp.) are advantageous for augmentative biological control because they reduce host populations before the damaging stages of the pest [1,2]
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
In Switzerland and Italy, Anastatus bifasciatus (Geoffroy) is the most prevalent native parasitoid successfully parasitizing H. halys eggs in the field [25,26,27]. It is one of the two European egg parasitoids capable of developing in viable H. halys eggs [26,28] and it was selected as a potential candidate for inundative biological control of H. halys in Europe
Summary
Egg parasitoids (e.g., Trichogramma spp.) are advantageous for augmentative biological control because they reduce host populations before the damaging stages of the pest [1,2]. Since its arrival in Switzerland, it has spread throughout many European countries [17] It is a pest of a wide variety of economically important vegetable, fruit, and leguminous crops as well as ornamentals in both its native and invaded range [18,19]. In Switzerland and Italy, Anastatus bifasciatus (Geoffroy) is the most prevalent native parasitoid successfully parasitizing H. halys eggs in the field [25,26,27]. It is one of the two European egg parasitoids capable of developing in viable H. halys eggs [26,28] and it was selected as a potential candidate for inundative biological control of H. halys in Europe. Comprises more than 50 heteropteran and lepidopteran species and there are concerns that mass releases of A. bifasciatus might lead to undesired non-target effects [29,30]
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