Voltage‐sensitive sodium channel mutations S989P + V1016G in Aedes aegypti confer variable resistance to pyrethroids,DDT and oxadiazines

BACKGROUND

Aedes aegypti is a vector of several important human pathogens. Control efforts rely primarily on pyrethroid insecticides for adult mosquito control, especially during disease outbreaks. A. aegypti has developed resistance nearly everywhere it occurs and insecticides are used. An important mechanism of resistance is due to mutations in the voltage‐sensitive sodium channel (Vssc) gene. Two mutations, in particular, S989P + V1016G, commonly occur together in parts of Asia.

RESULTS

We have created a strain (KDR:ROCK) that contains the Vssc mutations S989P + V1016G as the only mechanism of pyrethroid resistance within the genetic background of Rockefeller (ROCK), a susceptible lab strain. We created KDR:ROCK by crossing the pyrethroid‐resistant strain Singapore with ROCK followed by four backcrosses with ROCK and Vssc S989P + V1016G genotype selections. We determined the levels of resistance conferred to 17 structurally diverse pyrethroids, the organochloride DDT, and oxadiazines (VSSC blockers) indoxacarb (proinsecticide) and DCJW (the active metabolite of indoxacarb). Levels of resistance to the pyrethroids were variable, ranging from 21‐ to 107‐fold, but no clear pattern between resistance and chemical structure was observed. Resistance is inherited as an incompletely recessive trait. KDR:ROCK had a > 2000‐fold resistance to DDT, 37.5‐fold cross‐resistance to indoxacarb and 13.4‐fold cross‐resistance to DCJW.

CONCLUSION

Etofenprox (and DDT) should be avoided in areas where Vssc mutations S989P + V1016G exist at high frequencies. We found that pyrethroid structure cannot be used to predict the level of resistance conferred by kdr. These results provide useful information for resistance management and for better understanding pyrethroid interactions with VSSC. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Molecular studies of knockdown resistance to pyrethroids: cloning of domain II sodium channel gene sequences from insects

Knockdown resistance (kdr) is a target-site resistance mechanism that confers nerve insensitivity to DDT and pyrethroid insecticides. In the housefly, Musca domestica, molecular cloning of the para-type sodium channel gene has revealed two amino acid mutations that are associated with kdr and super-kdr resistance phenotypes. Both mutations are located in the domain II region of the channel; Leu1014 to Phe in the hydrophobic segment IIS6 and Met918 to Thr in the IIS4-IIS5 linker. To investigate whether these mutations also occur in other insects, we have designed degenerate primers based on conserved sequences in the domain II region of the sodium channel and used these to PCR amplify this region from insecticide-susceptible strains of eight diverse insect species representing four different insect Orders: Helicoverpa armigera, Plutella xylostella, Spodoptera littoralis (Lepidoptera), Blattella germanica (Dictyoptera), Tribolium castaneum (Coleoptera), Myzus persicae, Aphis gossypii and Phorodon humuli (Hemiptera). The primers amplified closely related para-type sodium channel sequences from each insect with a minimum of 85% amino acid identity between species. All of the sequences contained ‘susceptible’ Leu and Met residues at the positions associated with kdr and super-kdr resistance in the housefly. Recent results detailing the presence of a kdr-type Leu to Phe mutation in pyrethroid-resistant strains of two important agricultural pests, P. xylostella and M. persicae, are discussed. ©1997 SCI     

Diversity and frequencies of genetic mutations involved in insecticide resistance in field populations of the house fly (Musca domestica L.) from China

Insecticides have been extensively used for house fly control in China, with dichlorvos and deltamethrin being widely used. Knowledge about the current status of insecticide resistance and the underlying genetic changes is crucial for developing effective fly control strategies. The susceptibility to dichlorvos and deltamethrin, and the frequencies of genetic mutations involved in insecticide resistance were studied in five field populations of the house fly collected across China. Bioassay results show that flies exhibit 14- to 28-fold resistance to dichlorvos and 41- to 94-fold resistance to deltamethrin, indicating that dichlorvos and deltamethrin resistance are common in house fly populations in China. Molecular analysis reveals that flies from the five various locations carry resistance alleles at multiple loci and have diverse allelic types, different relative frequencies and combinations of each allele. Four non-synonymous single nucleotide polymorphisms (SNPs) (i.e. V260L, G342A/V, F407Y) in acetylcholinesterase (Ace) and two mutations (W251L/S) in a carboxylesterase (MdαE7) were commonly present in the field house flies. The L1014H rather than L1014F mutation in the voltage sensitive sodium channel gene (Vssc) was widely distributed in Chinese house flies. CYP6D1v1, which confers pyrethroid resistance, was found in all the five tested populations in China, although its frequency in house fly from Shandong province was very low. Our results suggest that resistance monitoring and management of house flies should be customized for a given location.