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 F2 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 LC50 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 LC50 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.

Resumo -O objetivo deste trabalho foi identificar espécies com alta produção de fitomassa, para proteção do solo no período de pousio. O experimento foi realizado com três espécies da família Leguminosae e três da família Poaceae, de 2009 a 2010, na área experimental do campus da Universidade Federal de Lavras, Minas Gerais. As espécies avaliadas foram: crotalária anagiroide (Crotalaria anagyroides), feijão-de-porco (Canavalia ensiformis), guandu-anão (Cajanus cajan), aveia-preta (Avena strigosa), sorgo (Sorghum bicolor) e milheto (Pennisetum glaucum), semeadas em cultivo solteiro e consorciado. O feijão-de-porco e o sorgo apresentaram as maiores taxas de cobertura do solo em cultivo solteiro, enquanto o milheto apresentou a menor. O sorgo, em cultivo solteiro e consorciado com feijão-de-porco e guandu-anão, apresenta a maior produção de matéria verde e matéria seca, enquanto o guandu-anão apresenta a menor produção de matéria verde, e a crotalária anagiroide, a menor produção de matéria seca. Por ocasião da implantação da cultura comercial, o tratamento que proporcionou a maior quantidade de palha sobre o solo foi o consórcio entre feijão-de-porco e sorgo.Termos para indexação: Avena strigosa, Cajanus cajan, Pennisetum glaucum, Sorghum bicolor, cultivo consorciado, taxa de cobertura. Agronomic performance of cover crops used as ground cover mulching in the fallow periodAbstract -The objective of this work was to identify species with high production of phytomass for ground cover in the fallow period. The experiment was carried out from 2009 to 2010, with three species of the family Leguminosae and three of the family Poaceae, in the experimental area of the campus of the Universidade Federal de Lavras, Minas Gerais, Brazil. The evaluated species were: caracas rattlebox (Crotalaria anagyroides), jack bean (Canavalia ensiformis), pigeon pea (Cajanus cajan), black oat (Avena strigosa), sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum), sown with and without intercropping. Jack bean and sorghum showed the highest rate of soil covering in single cropping, whereas pearl millet the lowest. Sorghum in single cropping and intercropped with jack bean and pigeon pea shows the largest production of green matter and dry matter, whereas pigeon pea presents the lowest production of green matter, and caracas rattlebox the lowest production of dry matter. At the implantation of the commercial culture, the largest amount of straw above the soil was provided by the intercropping between jack bean and sorghum.