Dose-response and sublethal effects from insecticide and adjuvant exposure on key behaviors of Trissolcus japonicus

Abstract

In its native range, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is a main egg parasitoid of Halyomorpha halys (Stål) (Hemiptera; Pentatomidae). Adventive populations of this parasitoid have been spreading in Europe and North America, allowing active distribution efforts in these areas to utilize it against H. halys in agriculture. We tested exposure of adults and parasitized egg masses to residues of a range of insecticides an adjuvant that the wasp could encounter in perennial horticultural crops, and how exposure might affect key behaviors. The insecticides included Burkholderia rinojensis, Methoxyfenozide, Sulfoxaflor, and Spinosad, and the adjuvant NuFilm®P. The lethal effects were investigated after exposure for 1, 6, and 24 hours to residues applied to Munger cells using a Potter spray tower to determine mortality levels. Sulfoxaflor and Spinosad resulted in 73% and 100% mortality after 24 hours at field rates, while Methoxyfenozide caused 19% mortality at the same rate. Little mortality occurred with Burkholderia rinojensis and NuFilm®P at recommended rates after 24 hours. Regarding sublethal effects, Spinosad, Sulfoxaflor, and Burkholderia rinojensis negatively impacted reproduction. Sulfoxaflor caused a lower angular velocity in parasitoids exposed to H. halys traces. Spinosad, Methoxyfenozide, and NuFilm®P induced a significantly lower overall circadian activity. Our results showed that precision timing of insecticide sprays to pests is necessary, especially for biocontrol programs that involve the release of parasitoids such as T. japonicus. Our results also illustrate how sensor data acquisition and behavioral analysis software can be utilized to detect important sublethal effects such as circadian disruption in minute parasitoids.