Esterase isozymes in Lygus hesperus: Characterization and relationship with organophosphate resistance

Esterases of Lygus hesperus Knight from five field and one laboratory populations were separated by non-denaturing polyacrylamide gel electrophoresis and were characterized for inhibition and substrate specificity. There were six zones of esterase activity toward naphthyl ester substrates. Significant inter- and intra-populational polymorphisms were observed. All the isozymes were carbo-xylesterases that were sensitive to inhibition by paraoxon and insensitive to eserine or EDTA (ethylenedinitrilotetraacetic acid). Carboxylesterases from L. hesperus more readily hydrolysed naphthyl esters with short side chains. Molecular weight estimation by non-denaturing polyacrylamide gel electrophoresis revealed that Est-1, the specific band of older females and eggs, contained two enzymes with relative molecular masses of 140000 and 112000. The four esterase allozymes in Est-3 had an average relative molecular mass of approximately 106000. The frequency of one putative allozyme in Est-3 was directly correlated with the LC₅₀ values of trichlorfon (to which L. hesperus has become resistant). The developmental and distribution variability of the esterase isozymes are compared.