Abstract
Indoxacarb is an important insecticide for the selective control of Helicoverpa armigera. It can be bioactivated to the more effective N-decarbomethoxylated indoxacarb (DCJW) by esterases in pests. It was observed that both field and laboratory selected populations of H. armigera showed negative cross-resistance between indoxacarb and methoxyfenozide. The Handan population exhibited moderate resistance to indoxacarb, but was susceptible to methoxyfenozide; the Baoding and Yishui populations exhibited moderate resistance to methoxyfenozide, but they were susceptible to indoxacarb. Moreover, the toxicity of indoxacarb was enhanced 1.83-fold in the laboratory methoxyfenozide-resistant H. armigera, and susceptibility to methoxyfenozide was increased 2.81-fold in the laboratory indoxacarb-resistant H. armigera. In vivo, DCJW concentrations in the susceptible and methoxyfenozide-selected (laboratory methoxyfenozide-resistant) populations were 4.59- and 4.31-fold greater than in the indoxacarb-resistant Handan population 1 h after dosing. After 2 h, the highest concentrations of DCJW and indoxacarb appeared in the methoxyfenozide-selected population. Meanwhile, increased carboxyl esterase (CarE) and decreased glutathione S-transferase (GST) activities were observed in the methoxyfenozide-selected population. However, the indoxacarb-selected (laboratory indoxacarb-resistant) and Handan populations showed a higher disappearance of indoxacarb and DCJW, and the activity of cytochrome P450 mono-oxygenase in these populations were significantly increased. This study showed that the improved toxicity of indoxacarb, as observed in the methoxyfenozide-selected H. armigera, was correlated with increased CarE activity, decreased GST activity, and the in vivo accumulation of indoxacarb and DCJW. The significantly increased cytochrome P450 activity and higher disappearance of indoxacarb and DCJW in indoxacarb-resistant H. armigera resulted in the decreased toxicity of indoxacarb.
Highlights
Cotton bollworm Helicoverpa armigera (Hübner; Lepidoptera: Noctuidae) is a global agricultural pest that damages a huge variety of cultivated crops, such as maize, cotton, tomatoes, and wheat [1].The larvae of H. armigera prefer to make holes and feed on blooms, flower heads, and fruits
Indoxacarb and its activated metabolite DCJW have a novel mode of action that involves the blocking of sodium channels, which results in the paralysis and death of the targeted species [6]
Indoxacarb has high efficacy against lepidopteran pests, H. armigera with moderate resistance to indoxacarb was detected in certain areas in China, such as the city of Handan, Hebei province
Summary
Cotton bollworm Helicoverpa armigera (Hübner; Lepidoptera: Noctuidae) is a global agricultural pest that damages a huge variety of cultivated crops, such as maize, cotton, tomatoes, and wheat [1]. Toxics 2020, 8, 71 and enhanced ability to develop resistance to a variety of insecticide classes [2,3] This pest’s increased resistance to conventional insecticides such as organophosphates, organochlorines, pyrethroids, and carbamates, makes the implementation of a comprehensive and tailor-made resistance-management program of primary importance [4]. To adequately control this pest, various classes of insecticides with different modes of action have been used, including indoxacarb and methoxyfenozide. We evaluated the metabolic activation of indoxacarb to DCJW in four populations of H. armigera with varying susceptibility levels to indoxacarb and methoxyfenozide. Detoxification-enzyme activities in the larval midgut were measured
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