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Molecular mechanisms of esterase-mediated insecticide resistance in the greenbug, Schizaphis graminum (Rondani) (Homoptera: Aphididae)
Abstract
The molecular basis for resistance to organophosphate insecticides in greenbugs, Schizaphis graminum (Rondani), was investigated. Two resistant populations (Type I and Type II) exhibited of two distinct enhanced esterase isozymes. Restriction digests of genomic DNA from susceptible, Type I, and Type II individuals probed with a fragment of the E4 esterase gene which confers organophosphate resistance in the green peach aphid, Myzus persicae (Sulzer), indicated similarity of esterase gene fragments in the two aphid species. Nested-PCR performed on greenbug genomic DNA with a Type I-specific degenerate primer paired with an esterase active site primer and two E4-specific internal primers resulted in a single product. Sequencing revealed that the fragment contained a region homologous to exon 2 of the E4 gene. Southern hybridization of genomic digests with HindIII and EcoRI probed with the Type I PCR product resulted in hybridization signal patterns in Type I digests different from those of susceptible and Type II digests. The susceptible and type II digests were indistinguishable regardless of the enzyme used. A number of fragments from the Type I strain produced in more intense signals, indicating that an esterase is amplified in Type I. The copy number of the greenbug esterase gene was estimated by digesting serial dilutions of genomic DNA with MspI and probing the blotted digests with the Type I fragment. Results indicated that Type I greenbugs contained four-to eight-fold higher number of copies of the gene than susceptible individuals. In summary, the molecular mechanism of esterase-mediated organophosphate resistance in the Type I strain appears to be due to gene amplification and is analogous the E4 gene of M. persicae. Although the Type II strain did not exhibit any evidence for gene amplification using the materials available, it is still possible that an esterase is amplified in the Type II genome but was not detected in this study. Evolutionary implications of the similarities between esterase E4 and the Type I esterase are also discussed.
Subject Area
Molecular biology|Entomology
Recommended Citation
Ono, Midori, "Molecular mechanisms of esterase-mediated insecticide resistance in the greenbug, Schizaphis graminum (Rondani) (Homoptera: Aphididae)" (1998). ETD collection for University of Nebraska-Lincoln. AAI9826095.
https://digitalcommons.unl.edu/dissertations/AAI9826095