Boosting the numbers of a tiny parasitic wasp could help control the brown marmorated stink bug (Halyomorpha halys), an invasive pest threatening crops including apples, cherries and corn.
In the first large-scale European field trial of a biological control against H. halys, mass releases of the wasp (Anastatus bifasciatus) in parts of northern Italy increased parasitism of the bug鈥檚 eggs. The wasp, which is native to Europe, lays its eggs inside the eggs of the pest, where its young develop by feeding on the host egg.
of Bioplanet, a biocontrol company, and her colleagues released 325,000 of the wasps over the summer of 2020. This took place at 11 orchards where the pest was known to be present, at a rate of 1000 per hectare.
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The team then collected stink bug eggs, which usually occur in deposits, or masses, of 20 to 30 eggs, in the field to establish how many had been discovered by the wasps and how effectively they had been attacked. At release sites, A. bifasciatus discovered 31 per cent of the stink bug egg masses and adult wasps emerged from 17 per cent of the discovered eggs, while at comparative sites where no release took place, these rates were 1.7 and 1.2 per cent, respectively.
In addition to these increases, the researchers found that the release of A. bifasciatus had no effect on parasitism by naturally occurring wasps of the same species, as well as by Trissolcus mitsukurii, an invasive wasp that also targets the bug鈥檚 eggs.
The native wasp has been undervalued as a potential biological control of H. halys, says Iacovone. Its true impact is likely to be even greater than simply looking at successful parasitism suggests, since adult wasps also feed intensively on the stink bug eggs.
Other parasitic wasps are also under consideration for control of the stink bug, with trial releases of the non-native species Trissolcus japonicus under way in Italy.
鈥�Anastatus bifasciatus is a common egg parasitoid in parts of Europe and this report is encouraging, showing that augmentative releases of this species enhance parasitism of brown marmorated stink bug egg masses,鈥� says at the Royal Horticultural Society in the UK, who wasn鈥檛 involved in the research.
Though the results show promise, very little is known about the current distribution and ecology of the wasp, says Powell. With models suggesting H. halys could establish as far north as the south of England, greater understanding about this and other potential natural enemies is needed.
Biological Control
