The impact of thiamethoxam on the feeding and behavior of 2 soybean herbivore feeding guilds

Abstract

Over the past few decades, inadvertent consequences have stemmed from the intensified use of neonicotinoids in agroecosystems. Neonicotinoid applications can result in both positive (e.g., reduced persistent virus transmission) and negative (e.g., increased host susceptibility) repercussions exhibiting ambiguity for their use in crop production. In soybean, aspects of neonicotinoid usage such as the impact on nonpersistent virus transmission and efficacy against nontarget herbivores have not been addressed. This study evaluated the interaction between the neonicotinoid thiamethoxam and soybean variety and the impact on different pest feeding guilds. Feeding and behavioral bioassays were conducted in the laboratory to assess the effect of thiamethoxam on the mortality and weight gain of the defoliator, Chrysodeixis includens (Walker). Bioassays evaluated impacts dependent and independent of soybean tissue, in addition to both localized and systemic efficacy within the soybean plant. Additionally, using the electrical penetration graph technique (EPG), the probing behavior of 2 piercing-sucking pests, Aphis gossypii Glover and Myzus persicae (Sulzer), was observed. Results from defoliator bioassays revealed thiamethoxam had insecticidal activity against C. includens. Distinctions in thiamethoxam-related mortality between bioassays dependent and independent of soybean tissue (~98% versus ~30% mortality) indicate a contribution of the plant towards defoliator-related toxicity. Observations of defoliator feeding behavior showed a preference for untreated soybean tissue relative to thiamethoxam-treated tissue, suggesting a deterrent effect of thiamethoxam. EPG monitoring of probing behavior exhibited a minimal effect of thiamethoxam on piercing-sucking herbivores. Findings from this study suggest neonicotinoids like thiamethoxam may provide some benefit via insecticidal activity against nontarget defoliators.

Thiamethoxam-Induced Intergenerational Sublethal Effects on the Life History and Feeding Behavior of Rhopalosiphum padi

“…EPG monitoring of probing behavior exhibited a minimal effect of thiamethoxam on piercing-sucking herbivores [ 54 ]. The effects of thiamethoxam sublethal concentrations (LC 5 and LC 10 ) on the feeding pattern of both parental and progeny R. padi were also investigated in this context by using electric penetration graph recordings (EPG).…”

The Effect of Different Thiamethoxam Concentrations on Riptortus pedestris Development and Fecundity

“…In addition, thiamethoxam is applied through seed coating in soybean and does not affect seed germination [67]. Thiamethoxam and its main metabolite (clothianidin) exhibited a less notable effect on nontarget piercing-sucking herbivores and the earthworm Eisenia fetida (Oligochaeta: Lumbricidae) [68,69]. Thiamethoxam is a degradable pesticide that has a half-life period of 7.1-92.3 days in European field soil [70].…”