Laboratory and field survival of Spodoptera frugiperda (Lepidoptera: Noctuidae) on Bt and non‐Bt maize and its susceptibility to insecticides

Abstract

BACKGROUND: Field-evolved resistance of fall armyworm (FAW), Spodoptera frugiperda (Smith), has been reported to Bt maize technologies in Brazil. The control failures of FAW by Bt maize increased the use of insecticides for their control. However, no information is available on the interaction between resistant FAW and their response to insecticides. Here, we evaluated the survival of FAW strains on Bt and non-Bt maize in laboratory and field conditions, and their susceptibility to insecticides. RESULTS: In the laboratory, resistant FAW larvae reared on Bt and non-Bt maize showed a similar susceptibility to spinetoram (LC 50 = 0.16-0.18 g a.i. cm −2 ) and chlorfenapyr (LC 50 = 0.17-0.20 g a.i. cm −2 ). However, their susceptibility was lower than that of the susceptible strain reared on non-Bt maize: LC 50 = 0.05 (spinetoram) and 0.08 (chlorfenapyr) g a.i. cm −2 . In contrast, heterozygous strains had similar susceptibility to the susceptible strain. In field trials, no differences in FAW survival were detected between strains when the commercial dose of two insecticides was applied in Bt and non-Bt maize.CONCLUSION: FAW strains surviving on Bt and non-Bt maize, at the same development stage, have similar susceptibility to insecticides. The integrated pest management practices and insect resistance management importance of these results are discussed.

Detection of a ryanodine receptor target‐site mutation in diamide insecticide resistant fall armyworm, Spodoptera frugiperda

“…Because of the evolution of resistance of FAW to some Bt proteins expressed in corn in Brazil, the use of chemical insecticides has increased in some corn‐producing regions . However, frequent reports of resistance to major chemical insecticides such as spinosad, lambda ‐cyhalothrin, chlorpyrifos and lufenuron, challenges the control of this pest.…”

“…42,43 Both amino acid residues have also been shown to be mutated in diamide-resistant tomato leafminer and rice stem borers. 35,40,44 Despite increasing selection pressure, particularly in Brazil, 45,46 high levels of diamide field resistance in noctuid pests conferred by RyR target-site mutations, as described for some non-noctuid lepidopterans, have not been reported. High levels of FAW resistance to diamides (resistance ratios of 160-and 500-fold against chlorantraniliprole and flubendiamide, respectively) due to frequent applications were recently found in a Puerto Rico population, but the mechanism of diamide resistance was not investigated.…”

Cross-crop resistance of Spodoptera frugiperda selected on Bt maize to genetically-modified soybean expressing Cry1Ac and Cry1F proteins in Brazil

“…Currently, field populations of S. frugiperda are composed predominantly of insects carrying Cry1Ab, Cry1F, and Cry1A.105 resistance alleles 26,28,[49][50][51] , reflected by the increasing use of insecticide applications in fields cultivated with crops expressing these proteins 52 . For example, on single or pyramided Bt maize technologies expressing Cry1 and Cry2 proteins up to four insecticidal sprays may be needed to manage S. frugiperda, under extreme infestations 52,53 . Based on this, it is expected that Cry1Ac/Cry1F-soybean may not provide stand-alone protection against S. frugiperda under Brazilian field conditions, making this species a non-target pest of this Bt technology.…”

“…Two putative S. frugiperda resistant colonies were selected from a field population collected in maize in Paulínia, São Paulo, Brazil (22° 42′ 38′′ S and 47° 06′ 26′′ W) using the F 2 screen method developed by Andow and Alstad 57 . The selection and rearing of resistant colonies was described in detail by Muraro et al 53 . The homozygous-resistant strains used in this study were H-R (selected for resistance to Cry1F-maize) and P-R (selected for resistance to Cry1F/Cry1A.105/Cry2Ab2-maize).…”

“…To evaluate putative heterozygous insects, the crossing between resistant♀ × susceptible♂ were performed. We only used heterozygotes from this cross because inheritance of resistance is autosomal inherited, and heterozygous larvae have demonstrated similar mortality-response to Bt proteins in diet and leaf bioassays 25,[27][28][29]33,53 .…”