Inheritance patterns, cross‐resistance and synergism in <scp><i>Spodoptera frugiperda</i></scp> (Lepidoptera: Noctuidae) resistant to emamectin benzoate
Dionei Schmidt Muraro, Dyrson de Oliveira Abbade Neto, Rubens Hideo Kanno, Ingrid Schimidt Kaiser, Oderlei Bernardi, Celso Omoto
Abstract
Abstract BACKGROUND Fall armyworm, Spodoptera frugiperda (J. E. Smith), is a relevant global pest due to severe damage caused on agricultural crops and its capacity to evolve resistance to insecticides. Here, we selected a strain of S. frugiperda resistant to emamectin benzoate under laboratory conditions to understand the inheritance patterns, cross‐resistance and synergism involved in the resistance. RESULTS The emamectin benzoate‐resistant (Ben‐R) strain was isolated by using F 2 screen in a field population collected in Lucas do Rio Verde, Mato Grasso state, Brazil. After ten generations of selection pressure with emamectin benzoate, the estimated LC 50 of the Ben‐R strain was 678.38 μg a.i. mL −1 whereas that of the susceptible (Sus) strain was 0.29 μg a.i.mL −1 , resulting in a resistance ratio (RR) of 2340‐fold. The LC 50 values of the offspring from reciprocal crosses of Sus and Ben‐R strains were 93.37 and 105.32 μg a.i. mL −1 , suggesting that resistance is an autosomal incompletely dominant trait. The high survival of heterozygous and Ben‐R strains (>92%) on non‐Bt maize sprayed with the field rate of emamectin benzoate confirmed that resistance is functionally dominant. The minimum number of segregations influencing resistance was 3.55, suggesting a polygenic effect. Low cross‐resistance was detected between emamectin benzoate and the insecticides methomyl, chlorpyrifos, lambda‐cyhalothrin, spinetoram, indoxacarb and chlorantraniliprole (RR <5.75‐fold). There was no effect of synergists piperonyl butoxide, diethyl maleate and S, S, S ‐tributyl phosphorotrithiotate on the Ben‐R strain, suggesting a minor role of metabolic resistance. CONCLUSIONS Our results showed a high risk of resistance evolution of S. frugiperda to emamectin benzoate, based on incompletely dominant inheritance. Rotation of insecticides with different modes of action can be one of the resistance management strategies to be implemented to delay the evolution of resistance of S. frugiperda to emamectin benzoate in Brazil.