Deletion of the nicotinic acetylcholine receptor subunit gene Dα1 confers insecticide resistance, but at what cost?

Abstract

Nicotinic acetylcholine receptors (nAChRs) have vital functions in processes of neurotransmission that underpin key behaviors. These pentameric ligand-gated ion channels have been used as targets for insecticides that constitutively activate them, causing the death of insect pests. In examining a knockout of the Dα1 nAChR subunit gene, our study linked this one subunit with multiple traits. We were able to confirm previous work that had identified Dα1 as a target of the neonicotinoid class of insecticides. Further, we uncovered roles for the gene in influencing mating behavior and patterns of sleep. The knockout mutant was also observed to have a significant reduction in longevity. This study highlighted the severe fitness costs that appear to be associated with the loss of function of this gene in natural populations in the absence of insecticides targeting the Dα1 subunit. Such a fitness cost could explain why target site resistances to neonicotinoids in pest insect populations have been associated specific amino acid replacement mutations in nAChR subunits, rather than loss of function. That mutant phenotypes were observed for the two behaviors examined indicates that the functions of Dα1, and other nAChR subunits, need to be explored more broadly. It also remains to be established whether these phenotypes were due to loss of the Dα1 receptor and/or to compensatory changes in the expression levels of other nAChR subunits.

Functional characterization and fitness cost of spinosad-resistant alleles in Ceratitis capitata

“…We found that the effect on the biological traits tested was moderate, with Q68* (Ccα6 3aQ68*Δ3b-4 /Ccα6 3aQ68*Δ3b-4 ) and Q68*-K352* (Ccα6 3aQ68*-K352* /Ccα6 3aQ68*-K352* ) isolines showing longer developmental time but higher male weight than C strain, whereas females of both resistant isolines and susceptible C strain did not differ in weight. However, mutations that would lead to a loss-of-function phenotype may affect behavioral patterns, as it has been reported for a Dα1 knockout mutant with a significant fitness cost in terms of severe mating behavior defects and an altered sleep phenotype (Somers et al 2017). Thus, we explored the possibility that behavioral fitness traits (parapheromone detection by wind tunnel and electrophysiological antennal assays, and mating success) could be affected in males of the Q68* and Q68*-K352* isolines.…”

“…The need to investigate fitness, behavioral and life-history traits that require the function of receptors being targeted by insecticides has been highlighted (Perry and Batterham 2018). While nAChRs may have many roles in behavior, the known roles for the different subunits identified in D. melanogaster currently include sleep (Dα1, Dα3 and Dα4- Shi et al 2014;Somers et al 2017;Wu et al 2014), courtship (Dα1- Somers et al 2017) and escape response (Dα7- Fayyazuddin et al 2006). Only a few studies have considered how spinosad resistance affects behavior and the impact that loss-of-function or truncated α6 transcripts could have.…”

Genomics, cys-loop ligand-gated ion channels and new targets for the control of insect pests and vectors

“…Genome editing with CRISPR/Cas9 or the use of model organisms such as D. melanogaster with the function of whole genes effectively removed may help to answer this question. Indeed, D. melanogaster with a knockout of the α1 nAChR gene was resistant to imidacloprid and nitenpyram [19]. Consistent with this, it was found that RNAi of α1 in Leptinotarsa decemlineata decreased sensitivity to imidacloprid and thiamethoxam [20].…”

Genetics and mechanisms of insecticide resistance in Ceratitis capitata and its implications for resistance management

“…We found that the effect on the biological traits tested was moderate, with Q68* (Ccα6 3aQ68*Δ3b-4 /Ccα6 3aQ68*Δ3b-4 ) and Q68*-K352* (Ccα6 3aQ68*-K352* /Ccα6 3aQ68*-K352* ) isolines showing longer developmental time but higher male weight than C strain, whereas females of both resistant isolines and susceptible C strain did not differ in weight. However, mutations that would lead to a loss-of-function phenotype may affect behavioral patterns, as it has been reported for a Dα1 knock-out mutant with a significant fitness cost in terms of severe mating behavior defects and an altered sleep phenotype (Somers et al, 2017a). Thus, we explored the possibility that behavioral fitness traits (parapheromone detection by wind tunnel and electrophysiological antennal assays, and mating success) could be affected in males of the Q68* and Q68*-K352* isolines.…”

“…Only a few studies have considered how spinosad resistance affects behavior and the impact that loss of function or truncated α6 transcripts could have, despite nAChRs may have many roles in behavior (Perry and Batterham, 2018). The known roles for the different subunits identified in D. melanogaster currently include sleep, Dα1, Dα3 and Dα4 (Shi et al, 2014;Wu et al, 2014;Somers et al, 2017a), courtship, Dα1 (Somers et al, 2017a) and escape response, Dα7 (Fayyazuddin et al, 2006). Changes to feeding behavior in Frankliniella occidentalis (Li et al, 2017) and reduced competitive mating in Heliothis virescens (Wyss et al, 2003) have been reported, but the molecular basis for spinosad resistance was unknown in both cases.…”