Aldehyde oxidase is coamplified with the World's most common Culex mosquito insecticide resistance-associated esterases

The evolution and spread of insecticide resistance is an important factor i n human disease prevention and crop protection. The mosquito Culex quinquef asciatus is the main vector of the disease filariasis and a member of a spe cies complex which is a common biting nuisance worldwide. The common insect icide resistance mechanism in this species involves germline amplification of the esterases est alpha 2(1) and est beta 2(1). This amplification has a risen once and rapidly spread worldwide. Less common and more variable resi stance phenotypes involve coamplification of est alpha 3 and est beta 1, or individual amplification of a single est beta 1, different alleles of the same est alpha and est beta gene loci. Est alpha 2(1) and est beta 2(1) are on the same large fragment of amplified DNA (amplicon) 2.7 kb apart. We ha ve now shown that this amplicon contains another full-length gene immediate ly 5' of est alpha 2(1) which codes for a molybdenum-containing hydroxylase , with highest homology to aldehyde oxidase (AO) from other organisms. The full-length putative AO gene is not present on the est alpha 3/est beta 1 o r est beta 1 amplicons, but multiple truncated 5' ends of this gene are pre sent around the presumed est alpha 3/est beta 1 amplicon breakpoint. Polyme rase chain reaction (PCR) analysis of insecticide-susceptible genomic DNA d emonstrated that a different allele of the putative AO gene in its non-ampl ified form is immediately 5' of est alpha. The 'AO' gene on the est alpha 2 (1)/est beta 2(1) amplicon is expressed and resistant insects have greater AO activity. This AO activity is sensitive to inhibition by an aldehyde-con taining herbicide and pesticide. This enzyme may confer a selective advanta ge to these insects in the presence of insecticide, as AO in mammals is bel ieved to be important in the detoxification process of several environmenta l pollutants.