Irradiation-induced sterility in an egg parasitoid and possible implications for the use of biological control in insect eradication.

Classical biological control is a pest control tool involving the release of imported natural enemies. The Sterile Insect Technique (SIT) comprises releasing sexually sterile insects of a pest into the wild population for suppression or eradication. Both these approaches are environmentally friendly and their combination can result in a synergistic impact on pest populations and improve eradication. However, stringent regulation surrounding the introduction of biological control agents limits their use in eradication owing to the perceived risk of effects on non-target organisms. We investigated the irradiation biology of the egg parasitoid Trissolcus basalis to ascertain whether sterile parasitoids could mitigate the risk of potential sustained non-target impacts. Mated female T. basalis were gamma-irradiated at doses between 120 and 150 Gy and exposed to egg masses of their host Nezara viridula throughout their lifespans. This resulted in host mortality, despite a substantial reduction in developing parasitoid offspring, which followed a negative dose-response. There was no emergence of parasitoid offspring at 140 Gy and above. Irradiation did not affect oviposition behaviour but caused an increase in longevity. Consequently, sterile parasitoids could possibly alleviate concerns regarding the irreversibility of biological control release, which promotes further investigation of their potential role in eradication.

Egg Sterilisation of Irradiated Nezara viridula (Hemiptera: Pentatomidae).

Nezara viridula Linnaeus (Hemiptera: Pentatomidae) is a polyphagous pest of a wide range of economically important crops. Because the control of this species and other pentatomids relies primarily on insecticide application, investigation into the Sterile Insect Technique (SIT) is warranted. We aimed to investigate the irradiation biology of N. viridula for the potential application of SIT against this pest. Male and female N. viridula were gamma-irradiated at doses between 4 and 28 Gy and mated with both irradiated and nonirradiated conspecifics. Sterility of the resulting eggs followed a dose-response in each case. Irradiated males crossed with untreated females showed higher F1 egg sterility than crosses where the female was irradiated. The greatest F1 egg sterility was observed when both parents were irradiated. There was no obvious dose-response for the longevity of irradiated males, and for the fecundity of nonirradiated females mated with irradiated males. The fecundity of irradiated females appeared to decrease with irradiation dose. These results can be applied to a potential future application of SIT against N. viridula, but predominantly supports the ongoing development of SIT for Halyomorpha halys Stål (Hemiptera: Pentatomidae) and hemipteran pests in general.