Intraspecific variation in the Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) susceptibility to insecticides

Variabilidade intraespecífica na suscetibilidade de Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) a inseticidas

ABSTRACT

The looper caterpillar Chrysodeixis includens (Walker) is considered the main defoliating pest in soybean crops, which contributes to yield losses. Delaying its resistance to insecticides is a major challenge in its management. This study aimed to characterize the susceptibility of C. includens to flubendiamide, cyantraniliprole, spinetoram and methomyl, as well as to establish a diagnostic concentration for monitoring resistance. The insecticide was applied to the surface of the artificial diet. For the dose-response curve, concentrations that resulted in 5 to 99 % mortality were used to estimate the lethal concentrations (LC₅₀ and LC₉₉) and resistance ratios (RR₅₀ and RR₉₉). The diagnostic concentrations were based on concentrations that provided 90 to 99 % mortality in the susceptible reference population. For flubendiamide and methomyl, the decrease in the susceptibility resulted in estimated RR₅₀ of 6.2 to 24.2 and 4.4 to 19.6 times, respectively. For cyantraniliprole and spinetoram, there was little difference in susceptibility among the populations, with RR₉₉ lower than 6.1 times. Differences in the susceptibility of C. includens were evident from concentrations of 0.5053, 5.053, 0.1579 and 28.42 μg cm^-2, respectively for flubendiamide, cyantraniliprole, spinetoram and methomyl.

KEYWORDS:
Glycine max; Plusiinae; insecticide resistance