Aedes aegyptiCCEae3A carboxylase expression confers carbamate, organophosphate and limited pyrethroid resistance in a model transgenic mosquito
Authors: Poulton Beth C. , Colman Fraser , Anthousi Amalia , Sattelle David B. , Lycett Gareth J. 
Published: August 2023

Insecticide resistance is a serious threat to our ability to control mosquito vectors which transmit pathogens including malaria parasites and arboviruses. Understanding the underlying mechanisms is an essential first step in tackling the challenges presented by resistance. This study aimed to functionally characterise the carboxylesterase, CCEae3A, the elevated expression of which has been implicated in temephos resistance inAedes aegyptiandAedes albopictuslarvae. Using our GAL4/UAS expression system, already established in insecticide-sensitiveAnopheles gambiaemosquitoes, we produced transgenicAn. gambiaemosquitoes that express anAe. aegyptiCCEae3A ubiquitously. This new transgenic line permits examination of CCEae3A expression in a background which does not express the gene and allows comparison with existingAn. gambiaeGAL4-UAS lines. Insecticide resistance profiling of these transgenicAn. gambiaelarvae indicated significant increases in resistance ratio for three organophosphate insecticides, temephos (5.98), chloropyriphos (6.64) and fenthion (3.18) when compared to the parental strain. Cross resistance to adulticides from three major insecticide classes: organophosphates (malathion, fenitrothion and pirimiphos methyl), carbamates (bendiocarb and propoxur) and pyrethroid (alpha-cypermethrin) was also detected. Resistance to certain organophosphates and carbamates validates conclusions drawn from previous expression and phenotypic data. However, detection of resistance to pirimiphos methyl and alphacypermethrin has not previously been formally associated with CCEae3A, despite occurring inAe. aegyptistrains where this gene was upregulated. Our findings highlight the importance of characterising individual resistance mechanisms, thereby ensuring accurate information is used to guide future vector control strategies.

Author Summary

Insecticides are vital disease control tools against pathogen-transmitting mosquitoes. However, they are becoming less effective as mosquitoes develop resistance. Among the molecular changes that contribute to resistance, increased production of enzymes that break down/sequester the insecticide is common. InAe. aegyptimosquitoes, which spread many arboviruses, over-expression of the carboxylesterase enzyme, CEae3A, has been associated with resistance to certain insecticides used for vector control, particularly organophosphate compounds. However, multiple resistance enzymes/mechanisms are likely to be present in resistant mosquitoes at the same time. To examine the effect of CCEae3A expression in isolation, we utilised theAn. gambiaemosquito with its convenient access to GAL4/UAS technology to regulate gene expression. This enabled production of CCEae3A in a normally insecticide-sensitive mosquito strain, permitting expression without interference from other resistance mechanisms. As anticipated, resistance to organophosphates was observed in larvae expressing CCEae3A. In adults, resistance was also found against compounds from organophosphate, carbamate and pyrethroid insecticide classes, including two compounds for which there had been no previous association. As well directly linking CCEae3A expression to specific insecticide resistance, this transgenic line can be included in a panel expressing alternative enzymes to screen new insecticidal compounds for liability to existing resistance mechanisms.