Competition between two natural enemies of Halyomorpha halys
Halyomorpha halys (Heteroptera: Pentatomidae – formerly EPPO Alert List) is a highly polyphagous pest which is native to Asia. The solitary Asian egg parasitoid Trissolcus japonicus (Hymenoptera: Scelionidae) has been studied as a classical biological control agent against H. halys and has been released in Italy. Adventive populations of Trissolcus mitsukurii (Ashmead) (Hymenoptera, Scelionidae), a less well-studied egg parasitoid of Eastern Asia origin, have recently been found attacking H. halys in Italy and in neighbouring countries, Slovenia and France. Both species can co-occur in the same habitats and can compete for hosts. The foraging behaviour and the progeny production of both species was assessed under laboratory conditions with three different interspecific competition scenarios. For indirect competition (A), H. halys egg masses previously parasitized by the female of one species were offered to the competitor females after 0, 3, 5, or 7 days. For direct extrinsic competition, (B) females of each species were either introduced simultaneously (synchronous release) or (C) when half of the host egg mass had already been parasitized by the other species (asynchronous release). Both Trissolcus species were able to parasitize host eggs already parasitized by the other species, although the progeny production always favoured the species that arrived first on the host egg mass. However, in a synchronous release scenario, T. mitsukurii displayed more aggressive behaviour and spent more time defending the host egg mass compared to T. japonicus, resulting in a higher progeny production. For biological control of H. halys, the results suggest that a single-species release is the best strategy, since multiparasitism behaviour can result in lower reproductive potential.
Sources
Giovannini L, Sabbatini-Peverieri G, Simoni S, Cervo R, Hoelmer KA, Roversi PF (2022) Interspecific competition between Trissolcus japonicus and Trissolcus mitsukurii, two promising candidates for biocontrol of Halyomorpha halys. Biological Control. https://doi.org/10.1016/j.biocontrol.2022.105068