Resistance Status of Aedes albopictus and Aedes aegypti from Alabama and Florida and Analysis Cytochrome P450 Genes Expression Level Compared with Susceptible and Resistant Strains

Abstract

Aedes albopictus and Aedes aegypti can transmit severe human diseases including dengue fever and yellow fever. When they are serious, these diseases can lead to human death and economic burden. Ae. albopictus has already spread from its origin Asia to many continents, including North America. In the United States, this species can be found in Alabama, but the resistance status remains unknown. Part of my experiment analyzed the resistance status. Ae. albopictus from six locations in Alabama were tested and showed no significant resistance. Two main insecticide classes were used: organophosphates (OPs) and pyrethroids. For OPs, chlorpyrifos, malathion and fenitrothion were used. Malathion had the highest LC50 in these three insecticides ranging from 0.1ppm to 1.2ppm. The resistance status was similar between chlorpyrifos and fenitrothion ranging from 0.003ppm to 0.05ppm and from 0.01ppm to 0.1ppm respectively. For pyrethroids there were five insecticides used: deltamethrin, permethrin, resmethrin, etofenprox, and β-cyfluthrin. Resmethrin had a highest LC50 values ranging from 0.05ppm to 0.4ppm compared with other insecticides followed by permethrin ranging from 0.01ppm to 0.2ppm. In these eight insecticides chlorpyrifos has the highest efficacy while malathion has the last efficacy. Another part of my experiment was to test the resistance status of field Ae. aegypti in Florida and make comparison with susceptible (S-Lab) and resistant laboratory strains (PR). The result showed that field strains developed resistance to etofenprox, with a resistance ratio of 1400, permethrin had a ratio of 24, and malathion had a ratio of 11. Field strains developed high tolerance to β-cyfluthrin and chlorpyrifos with resistance ratios reaching 9.7 and 7.6. This strain was still susceptible to fenitrothion with resistance ratio of 0.3. Based on these results, Ae. aegypti in Florida has developed resistance and high tolerance to some insecticides. Cytochrome P450 genes are important in insecticide resistance. In this experiment the genes CYP4H30 and CYP6CB1 were chosen to analyze their expression level. For CYP4H30, there was no difference among AeFl, susceptible S-Lab, and resistant PR strains. But the expression level in AeFl and resistant PR strains were upregulated in CYP6CB1. The expression ratio of AeFl was 5.6 and that of PR strain was 33.3 compared to susceptible S-Lab strain.