Interspecific competition between Trissolcus japonicus and Trissolcus mitsukurii, two promising candidates for biocontrol of Halyomorpha halys.

The invasive stink bug Halyomorpha halys, native to east Asia, is a severe agricultural pest of worldwide importance and biocontrol is a promising method for its long-term management. The two Asian egg parasitoids Trissolcus japonicus and Trissolcus mitsukurii are considered to be effective candidates as biological control agents. These species can co-occur in the same habitats and interspecific competition for hosts could therefore have an important role in natural control. We assessed the foraging behavior and the progeny production of both species under laboratory conditions with three different interspecific competition scenarios. With indirect competition, 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. With direct extrinsic competition, females of each species were tested in arenas either when introduced simultaneously (synchronous release) or 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 favored the species that arrived first on the host egg mass. However, in the synchronous releases scenario, T. mitsukurii displayed more aggressive behavior and spent more time defending the host egg mass than T. japonicus, resulting in a higher progeny production. Our results showed that multiparasitism among T. japonicus and T. mitsukurii, at least under laboratory conditions, resulted in a general waste of searching time, energy, eggs laid, and a lower reproductive potential by the second-arriving species on the host egg mass.