Combination ofkdrmutation and detoxification gene expression associated with high tolerance for permethrin in a resistantAedes aegyptipopulation
Authors: Chen Tse-Yu , Smartt Chelsea T. , Shin Dongyoung 
Published: June 2020

Aedes aegypti, as one of the vectors transmitting several arboviruses, is a main target in mosquito control programs. Permethrin remains the major adulticide used to control these mosquitoes. The increasing percentage of permethrin resistantAedes aegyptihas become an important issue around the world. Knockdown resistance (kdr) is one of the major mechanisms related to permethrin resistance. On the other hand, detoxification genes including cytochrome P450 monooxygenases (P450) and glutathione S-transferases (GSTs) are also suggested as permethrin resistance apparatus. Here we selected a permethrin resistant (p-s)Aedes aegyptipopulation from Florida and compared its mortality after exposure, median lethal dose (LD50), adult survivorship and larval development to several field populations. We used allele-specific PCR genotyping of the S989P, V1016I and F1534C sites in the sodium channel gene and gene expression analysis of several p450 and GSTs genes before and after permethrin exposure to determine their involvement in permethrin sensitivity betweenAe. aegyptipopulations. Results indicated the p-s population had the highest resistance to permethrin based on LD50 and the mortality test. The larval development time did not significantly differ between the populations, however the p-s adults survived longer than the other populations. In the genotype study, p-s population had mostly homozygous mutations in all three mutant sites of the sodium channel gene. Detoxification gene expression studies showed that two p450 genes, AAEL009124 (CYP6N12) and, AAEL009127 (CYP6M11), were upregulated and, accession # AAEL006802, AAEL014891 (CYP6P12) and AAEL014619 (CYP9J22) were downregulated after 120 minutes of permethrin exposure in the p-s population. These results suggest that in highly permethrin resistantAedes aegyptipopulations bothkdrmutations and xenobiotic metabolism might be involved. Involvement of multiple mechanisms to achieve resistance to permethrin supports the need for implementing comprehensive mosquito control measures, such as an integrated pest management strategy, so that selection pressure for resistance is decreased without compromising control efforts while new methodologies are being developed.

Author summary

Pyrethroids have been applied as a major type of insecticide targeted atAedes aegypti, a key vector in the transmission of several flaviviruses. Resistance to pyrethroids has emerged and has become a worldwide threat to mosquito control. Pyrethroid resistance usually occurs with knockdown resistance (kdr) where the voltage gated sodium channel is mutated. We selected a permethrin resistant (p-s)Aedes aegyptipopulation from Florida and, along with two other field populations, examined three mutation sites, S989P, V1016I and F1534C. The data showed the p-s population had the most homozygous mutations which correlated to the permethrin resistance level. Besideskdr, detoxification genes also have been identified to have pyrethroid metabolizing abilities. We found two cytochrome P450 monooxygenases genes,CYP6N12andCYP6M11, were overexpressed in the p-s population after permethrin exposure, suggesting a role in resistance to permethrin. Together, our results provide information about potential mechanisms used in major vectors with high insecticide resistance.