ABSTRACT
BACKGROUND: Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), a major lepidopteran pest in Latin and North America, has very recently invaded the continents of Africa and Asia. FAW has evolved resistance to different insecticides and transgenic corn expressing Bacillus thuringiensis (Bt) toxins. Here, we investigated the extent and mechanisms of resistance to diamide insecticides in a Brazilian field-collected FAW strain selected using chlorantraniliprole. RESULTS: Continuous laboratory selection of a field-collected FAW strain with chlorantraniliprole resulted in resistance ratios of 225-fold and > 5400-fold against chlorantraniliprole and flubendiamide, respectively, when compared with a susceptible strain. Pre-exposure to different synergists known to inhibit detoxification enzymes did not result in significantly increased larval toxicity, suggesting a minor role for metabolic resistance. Sequencing of the FAW ryanodine receptor (RyR) C-terminal domains II to VI revealed a single nucleotide polymorphism, resulting in a I4734M mutation recently said to confer target-site resistance to diamides in lepidopteran pests. Genotyping by pyrosequencing of field-collected FAW larvae sampled in the 2018 crop season suggests a low resistance allele frequency. Furthermore, we developed a fluorescent polymerase chain reaction (PCR)-based allelic discrimination assay for rapid genotyping of field-collected FAW samples, because diamides are increasingly used in Bt-/non-Bt corn. CONCLUSIONS: Recently, the identified RyR mutation has been shown to confer field resistance in other lepidopteran pests such as diamondback moth, tomato leafminer and striped rice stem borer. The developed PCR-based allelic discrimination assay will help to monitor the frequency and future spread of diamide resistance allele in FAW field populations and help to implement appropriate resistance management measures. © 2019 Society of Chemical Industry.
Subject(s)
Spodoptera , Animals , Diamide , Insecticide Resistance , Insecticides , Larva , Mutation , Ryanodine Receptor Calcium Release ChannelABSTRACT
BACKGROUND: Understanding the genetic basis of insect resistance to insecticides can help to implement insecticide resistance management (IRM) strategies. In this study, we selected a strain of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) resistant to chlorantraniliprole using the F2 screen method, characterized the inheritance of resistance and evaluated patterns of cross-resistance to other diamide insecticides. RESULTS: The chlorantraniliprole-resistant strain (Chlorant-R) was selected from a field-collected population with an estimated allele frequency of 0.1316. The estimated median lethal concentration (LC50 ) values were 0.011 and 2.610 µg a.i. cm-2 for the susceptible (Sus) and Chlorant-R strains, respectively, resulting in a resistance ratio (RR) of 237-fold. The LC50 values of the reciprocal crosses were 0.155 and 0.164 µg a.i. cm-2 , indicating that resistance is autosomally inherited. Resistance was characterized as incompletely recessive and monogenic at concentrations close to the recommended field rates of chlorantraniliprole. Survival of the resistant strain and heterozygous larvae in maize plants treated at the field rate was â¼ 60 (similar to the susceptible strain on untreated maize) and 15%, respectively. The Chlorant-R strain showed low cross-resistance to cyantraniliprole (RR â¼ 27-fold) and very high cross-resistance to flubendiamide (RR > 42 000-fold). CONCLUSIONS: The frequency of chlorantraniliprole resistance allele was moderately high in a field-collected population of S. frugiperda. The inheritance of chlorantraniliprole resistance was characterized as autosomal, incompletely recessive and monogenic. S. frugiperda showed cross-resistance to other diamide insecticides. These results provide essential information for the implementation of IRM programs to preserve the useful life of diamide insecticides for controlling S. frugiperda in Brazil. © 2019 Society of Chemical Industry.
