Selection of organosilicone surfactants for tank-mixed pesticides considering the balance between synergistic effects on pests and environmental risks

Abstract In this study, the bioactivities of binary mixtures of organosilicone surfactants and indoxacarb against two Lepidopteran pests were investigated along with their environmental risks. All of the tested organosilicone surfactants had obvious synergistic effects on the contact toxicity of indoxacarb against Spodoptera exigua and Agrotis ipsilon . However, all of the organosilicone surfactants exhibited certain antagonism for indoxacarb against S. exigua in terms of stomach & contact toxicity; both Silwet-408 and Silwet-806 exhibited additivity against A. ipsilon , whereas Silwet-618 and Silwet-DRS-60 exhibited synergism and slight antagonism, respectively. All of the tested chemicals were highly toxic to Daphnia magna , among which Silwet-DRS-60 had the lowest acute toxicity (EC 50 of 94.91 μg/L). However, these chemicals were less toxic to Brachydanio rerio . Silwet-DRS-60 had a low toxicity to B. rerio , while Silwet-408, Silwet-806 and Silwet-618 were moderately toxic to B. rerio . For the joint toxicity evaluation of organosilicone surfactants and indoxacarb to D. magna and B. rerio , the additive index method, concentration addition method and toxicity unit method were robust in judging synergism or antagonism, whereas other methods were more conservative; the V-value method and equilibrium curve method exhibited high robustness and viability in evaluating the combined effects of binary mixtures. Overall, we should carefully select organosilicone surfactants for premixed or tank-mixed pesticides in agriculture to obtain a balance between synergistic effects on pests and environmental risks.