Rodrigues, J. G. | bioRxiv Science

bioRxiv2021

Susceptibility monitoring and the molecular characterization of resistance of Spodoptera frugiperda (Lepidoptera: Noctuidae) to lambda-cyhalothrin and chlorpyrifos

Spodoptera frugiperda (J. E. Smith) is a serious and widespread agricultural pest with several records of resistance to different insecticides and Bt proteins, including the neurotoxic insecticides chlorpyrifos (organophosphate) and lambda-cyhalothrin (pyrethroid). In this study, we (i) characterized and monitored the susceptibility of field populations of S. frugiperda to chlorpyrifos (194 populations) and lambda-cyhalothrin (197 populations) collected from major maize-growing regions of Brazil from 2003 to 2016, and (ii) compared gene expression levels of chlorpyrifos- and lambda-cyhalothrin-resistant strains to a susceptible reference strain (Sf-ss) of S. frugiperda. Laboratory-guided assays to monitor larval susceptibility detected average survival ranging from 29.3% to 36.0% to chlorpyrifos, and 23.1% to 68.0% to lambda-cyhalothrin at diagnostic concentration, based on LC99 of the susceptible reference strain of each insecticide. The resistance ratio of the chlorpyrifos-resistant strain (Clo-rr) was 25.4-fold and of the lambda-cyhalothrin-resistant strain (Lam-rr) was 217-fold. Differential gene expression analyses between resistant vs susceptible strains identified 1,098 differentially expressed genes (DEGs) between Clo-rr and Sf-ss, and 303 DEGs between Lam-rr and Sf-ss. Functional analyses of the DEGs revealed the up-regulation of several detoxification enzymes, mainly cytochrome P450 belonging to the CYP3 and CYP6 clans. Genes associated with regulatory processes, such as the forkhead box O (FoxO) were also up-regulated. Our data points that the resistance mechanisms of Clo-rr and Lam-rr strains of S. frugiperda to chlorpyrifos and lambda-cyhalothrin are mainly mediated by enzyme detoxification.

zoology↗

bioRxiv2020

There is more than chitin synthase in insect resistance to benzoylureas: Molecular markers associated with teflubenzuron resistance in Spodoptera frugiperda

Chitin synthesis inhibitors are successfully used in pest control and are an excellent option for use in integrated pest management programs due to their low non-target effects. Reports on field-evolved resistance of lepidopteran pests to chitin synthesis inhibitors and the selection of laboratory resistant strains to these products require a detailed investigation on the resistance mechanisms and on the identification of molecular markers to support the implementation of efficient monitoring and resistance management programs. Teflubenzuron is a chitin synthesis inhibitor highly effective in controlling lepidopteran pests, including nowadays the world widely distributed fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae). We report the selection of a laboratory strain of S. frugiperda resistant to teflubenzuron, and its use for the characterization of the inheritance of resistance, evaluation of cross-resistance to other chitin-synthesis inhibitors and the identification of a set of single nucleotide polymorphisms (SNPs) for use as candidate molecular markers for monitoring the evolution of resistance of S. frugiperda to teflubenzuron. The resistance of the selected strain of S. frugiperda to teflubenzuron was characterized as polygenic, autosomal, and incompletely recessive. The resistance ratio observed was nearly 1,365-fold. Teflubenzuron-resistant strain showed some cross-resistance to lufenuron and novaluron but not to chlorfluazuron. We also detected a set of 72 SNPs that could support monitoring of the resistance frequency to teflubenzuron in field populations. Our data contribute to the understanding of the resistance mechanisms and the inheritance of polygenic resistance of S. frugiperda to benzoylureas. We also contribute with candidate markers as tools for monitoring the emergence and spread of teflubenzuron resistance in S. frugiperda.

evolutionary biology↗