Comparative effects of insecticides with different mechanisms of action on Chrysoperla externa (Neuroptera: Chrysopidae): Lethal, sublethal and dose–response effects

Abstract

The comprehensive knowledge that the delayed systemic and reproduction side effects can be even more deleterious than acute toxicity, has caused a shift in focus toward sublethal effects assessment on physiology and behavior of beneficial insects. In this study, we assessed the risks posed by some insecticides with different mode of action through lethal and delayed systemic sublethal effects on the pupation, adult emergence, and reproduction of the chrysopid Chrysoperla externa (Hagen, 1861; Neuroptera: Chrysopidae), an important predator in pest biological control. The maximum field recommended dose (MFRD) and twice (2×MFRD) for chlorantraniliprole, tebufenozide, and pyriproxyfen were harmless to C. externa. In contrast, all the tested chitin synthesis inhibitors (CSIs) were highly detrimental to the predator, despite of their lack of acute lethal toxicity. Therefore, the safety assumed by using IGRs toward beneficial insects is not valid for chrysopids. Dose-response data showed that although all CSIs have a similar mechanism of action, the relative extent of toxicity may differ (novaluron > lufenuron > teflubenzuron). For CSIs, the delayed systemic effects became obvious at adult emergence, where the predicted no observable effect dose (NOED) was 1/2 048 of the MFRD for novaluron (0.085 ng/insect), and 1/256 of the MFRD for both lufenuron (0.25 ng/insect) and teflubenzuron (0.6 ng/insect). Finally, this work emphasized the significance of performing toxicity risk assessments with an adequate posttreatment period to avoid underestimating the toxicities of insecticides, as the acute lethal toxicity assays may not provide accurate information regarding the long-range effects of hazardous compounds.

Residual toxicity of four insecticides on larvae and adults of the predator Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae)

“…This insecticide, belonging to group 18 (IRAC, 2022), is a diacylhydrazine that acts as an agonist of ecdysteroid receptors (RIMOLDI et al, 2008). The selectivity of this compound against natural enemies such as parasitoids and predators was recognized (ZOTTI et al, 2013;ONO et al, 2017). Insecticides that inhibit chitin synthesis, such as methoxyfenozide, act mainly by ingestion, but some compounds may have contact toxicity and adversely af-fect reproductive parameters such as fecundity and especially fertility (ONO et al, 2017;SHAN et al, 2020).…”

“…In addition. they act mainly on lepidopteran larvae (ZOTTI et al, 2013;PEREZ AGUILAR et al, 2018). The low toxicity of this insecticide on larvae and adults observed in the present study corroborates the literature, confirming the selectivity against C. externa, but altered the fecundity and fertility of females in some tests, as reported with C. cubana in laboratory tests (ONO et al, 2017).…”

Perspective: common errors in dose–response analysis and how to avoid them

“…The authors also claimed that the efficacy of pyroxasulfone was around 4‐ to 11‐fold higher than that of s‐metolachlor, while no SEs were reported for these RI values to test for statistical significance. The relative potency of three insecticides (lufenuron, teflubenzuron and novaluron) on Chrysoperla externa (green lacewing) was estimated to be between 0.5 and 15, but no SEs were reported for these values 30 . A high RI to pymetrozine insecticide was reported for several populations of Bemisia tabaci (whitefly) without SEs and post hoc analysis 31 .…”

Effects of Tebufenozide on Eggs, Larvae and Adults of Chrysoperla carnea (Neuroptera: Chrysopidae)

“…Tebufenozide is a nonsteroidal ecdysone antagonist that stimulates the moulting hormone receptor of target insect pests, especially Lepidoptera, thereby inducing premature and lethal moulting [ 6 , 7 ]. IGRs are used against a range of pests in agroecosystems where C. carnea is an important natural enemy, and ecdysone antagonists are considered the most selective and, therefore, safer [ 8 , 9 , 10 , 11 ]. Nevertheless, while effects on natural enemies are less likely to be lethal, sublethal effects on their life history, performance, and behavior are possible [ 5 ].…”