Combined Non-Target Effects of Insecticide and High Temperature on the Parasitoid Bracon nigricans

We studied the acute toxicity and the sublethal effects, on reproduction and host-killingactivity, of four widely used insecticides on the generalist parasitoid Bracon nigricans(Hymenoptera: Braconidae), a natural enemy of the invasive tomato pest, Tuta absoluta(Lepidoptera: Gelechiidae). Laboratory bioassays were conducted applying maximuminsecticide label rates at three constant temperatures, 25, 35 and 40°C, considered as regular,high and very high, respectively. Data on female survival and offspring production wereused to calculate population growth indexes as a measure of population recovery after pesticideexposure. Spinetoram caused 80% mortality at 25°C and 100% at higher temperatures,while spinosad caused 100% mortality under all temperature regimes.Cyantraniliprole was slightly toxic to B. nigricans adults in terms of acute toxicity at the threetemperatures, while it did not cause any sublethal effects in egg-laying and host-killing activities.The interaction between the two tested factors (insecticide and temperature) significantlyinfluenced the number of eggs laid by the parasitoid, which was the lowest in thecase of females exposed to chlorantraniliprole at 35°C. Furthermore, significantly lower B.nigricans demographic growth indexes were estimated for all the insecticides under all temperatureconditions, with the exception of chlorantraniliprole at 25°C. Our findings highlightan interaction between high temperatures and insecticide exposure, which suggests a needfor including natural stressors, such as temperature, in pesticide risk assessmentsprocedures.