Abstract
Livestock production is an important economic activity in Brazil, which has been suffering significant losses due to the impact of parasites. The New World screwworm (NWS) fly, Cochliomyia hominivorax, is an ectoparasite and one of the most important myiasis-causing flies endemic to the Americas. The geographic distribution of NWS has been reduced after the implementation of the Sterile Insect Technique (SIT), being eradicated in North America and part of Central America. In South America, C. hominivorax is controlled by chemical insecticides, although indiscriminate use can cause selection of resistant individuals. Previous studies have associated the Gly137Asp and Trp251Leu mutations in the active site of carboxylesterase E3 to resistance of diethyl and dimethyl-organophosphates insecticides, respectively. Here, we have sequenced a fragment of the carboxylesterase E3 gene (ChαE7), comprising part of intron iII, exon eIII, intron iIII and part of exon eIV, and three mitochondrial gene sequences (CR, COI and COII), of NWS flies from 21 locations in South America. These markers were used for population structure analyses and the ChαE7 gene was also investigated to gain insight into the selective pressures that have shaped its evolution. Analysis of molecular variance (AMOVA) and pairwise FST analysis indicated an increased genetic structure between locations in the ChαE7 compared to the concatenated mitochondrial genes. Discriminant analysis of principal components (DAPC) and spatial analysis of molecular variance (SAMOVA) indicated different degrees of genetic structure for all markers, in agreement with the AMOVA results, but with low correlation to geographic data. The NWS fly is considered a panmitic species based on mitochondrial data, while it is structured into three groups considering the ChαE7 gene. A negative association between the two mutations related to organophosphate resistance and Fay & Wu’s H significant negative values for the exons, suggest that these mutations evolved under positive selection.
Highlights
Livestock production is an important economic activity in Brazil that is strongly affected by parasites
The New World screwworm (NWS) fly eII, eIII, iIII and eIV regions have been described previously [41], this is the first report of the intron iII sequence
Partial characterization of the carboxylesterase E3 ChαE7 gene allowed its use as a nuclear molecular marker for comparisons with previously studied mitochondrial markers [38,39] and for investigation of the genetic and geographic structure, demographic history and selection pressure of NWS fly populations inhabiting the southern region of the Amazon river basin
Summary
Livestock production is an important economic activity in Brazil that is strongly affected by parasites. The NWS fly was distributed from southern United States of America to Argentina and Uruguay [2,3,4] but the implementation of an area-wide integrated management approach (AW-IPM) based on the Sterile Insect Technique (SIT) reduced its distribution [4,5,6]. There are many crucial biological questions involving the management of insect pest populations that should be investigated in addition to political decisions and interests in order to achieve the objectives. These include understanding population distribution, detecting geographic barriers or environmental discontinuities limiting gene flow and determining population sizes in target areas [7,8]
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