Geographic Monitoring of Insecticide Resistance Mutations in Native and Invasive Populations of the Fall Armyworm

Abstract

Field evolved resistance to insecticides is one of the main challenges in pest control. The fall armyworm (FAW) is a lepidopteran pest species causing severe crop losses, especially corn. While native to the Americas, the presence of FAW was confirmed in West Africa in 2016. Since then, the FAW has been detected in over 70 countries covering sub-Saharan Africa, the Middle East, North Africa, South Asia, Southeast Asia, and Oceania. In this study, we tested whether this invasion was accompanied by the spread of resistance mutations from native to invasive areas. We observed that mutations causing Bt resistance at ABCC2 genes were observed only in native populations where the mutations were initially reported. Invasive populations were found to have higher gene numbers of cytochrome P450 genes than native populations and a higher proportion of multiple resistance mutations at acetylcholinesterase genes, supporting strong selective pressure for resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and resistance to various synthetic insecticides in Chinese populations. These results highlight the necessity of regular and standardized monitoring of insecticide resistance in invasive populations using both genomic approaches and bioassay experiments.

Genetic Screening to Identify Candidate Resistance Alleles to Cry1F Corn in Fall Armyworm Using Targeted Sequencing

“…Initial DNA-based resistance monitoring efforts for S. frugiperda focused on Taqman PCR targeting known mutations in the SfABCC2 gene [ 8 , 9 ] and pooled population sequencing [ 10 ]. More recently, whole-genome resequencing was used to detect the presence of five reported resistance alleles in S. frugiperda populations from 12 geographic locations [ 40 ]. As a more cost-effective alternative to whole-genome sequencing, we provide proof of concept for the use of targeted highly multiplexed PCR for monitoring a known resistance allele ( SfABCC2mut ) and using bioinformatics to identify novel candidate SfABCC2 resistance alleles.…”

“…We did find two heterozygote individuals from Lajas (PRL_168 and PRL_164) carrying a GY deletion (DGY784D in our model, allele frequency 0.0571) previously described in Cry1F-resistant and field-collected S. frugiperda from Brazil [ 10 ]. However, detection of this GY deletion in Cry1F-suceptible individuals from Brazil [ 40 ] questions the relevance of this mutation to resistance.…”

Baseline Susceptibility of Spodoptera frugiperda Populations Collected in India towards Different Chemical Classes of Insecticides

“…Target-site mutations conferring insecticide resistance and low field efficacy of older chemistries have been already reported from countries recently invaded [30,33], including India [34]. Therefore, it is important to establish an insecticide baseline susceptibility in FAW in India to make efficient decisions on what mode of action/chemical class to recommend for control [35].…”

Recent Advances in the Understanding of Molecular Mechanisms of Resistance in Noctuid Pests

“…Marked differences exist between FAW populations, which can provide guidance for appropriate resistance management decisions. Indeed, these studies show the presence of mutations in acetylcholinesterase, the target of carbamates and organophosphates, in both native and invasive populations, whereas only native populations show a deletion in ABCC2, the target of some Bt proteins [1,4]. In this case, diamide insecticides could be useful in the fight against FAW since none of the known mutations in the target of diamides, the ryanodine receptor, have been detected.…”

“…Some of the papers focus on the diagnosis to differentiate the two sympatric host plant species of FAW, maize and rice [1], or on the most suitable rearing conditions for this non-model species [2], while others tackle the development of molecular tools for the detection of mutations in insecticide targets conferring resistance [3]. Other studies have monitored the presence of known mutations in the targets of major insecticide classes by comparing native and invasive populations [1,4]. Marked differences exist between FAW populations, which can provide guidance for appropriate resistance management decisions.…”