Multiple effects of indoxacarb on the soybean caterpillar Anticarsia gemmatalis

The caterpillar, Anticarsia gemmatalis is one of the most important defoliating pests of soybean crops in the Americas. Control of A. gemmatalis, is primarily achieved with chemical insecticides; however, populations of this species have developed resistance to certain chemical molecules. Therefore, insecticides with different modes of action should be evaluated to control this pest. The objective of this study was to evaluate the effects of the insecticide indoxacarb on mortality, respiration, locomotor behavior, and midgut histology in A. gemmatalis caterpillars. After 72 h of exposure, indoxacarb was toxic to A. gemmatalis caterpillars, with 87 % survival in the control group and 54 %, 38 %, 24 %, and 0 % survival in those exposed to indoxacarb at LC₂₅ (2.14 g a.i. L⁻¹), LC₅₀ (3.08 g a.i. L⁻¹), LC₇₅ (4.42 g a.i. L⁻¹), and LC₉₀ (6.39 g a.i. L⁻¹), respectively. With increasing concentrations, the locomotor behavior of A. gemmatalis was altered, with shorter walking distances and longer resting time avoiding the treated area, indicating a strong repellent effect of the insecticide. The respiration rate of A. gemmatalis caterpillars decreased after exposure to indoxacarb. There was a reduction in food consumption by caterpillars treated with the insecticide, indicating a phagoinhibitory effect. In addition, histological changes were observed in the midgut of A. gemmatalis, including cytoplasmic vacuolization, an increased amount of cell fragments with nuclei released into the gut lumen, and degradation of the peritrophic matrix, indicating severe effects of cell degeneration. Indoxacarb caused both lethal and sublethal effects on A. gemmatalis, indicating its potential for the control of this pest.