Insecticide Resistance and Esterase Enzyme Variation in the California Red Scale (Homoptera: Diaspididae)

Abstract

A population of California red scale, Aonidiella aurantii (Maskell), was found to be resistant to the organophosphates chlorpyrifos and methidathion, and to the carbamate carbmyl when compared with a susceptible population. The esterase inhibitor S,S,S-tributyl phosphorotrithioate increased chloropyrifos toxicity in the resistant population to a greater extent than in the susceptible population, suggesting that esterase enzymes were involved in chlorpyrifos, but not methidathion or carbaryl resistance. The esterase banding patterns of both populations were characterized using cellulose acetate electrophoresis. As many as 5 esterase bands were detected in 2nd-instar females, early 3rd-instar nongravid females, late 3rd-instar nongravid females, 2nd-instar males, pupal males, and adult males. There was variation between sexes and stages of scale in the relative mobility, frequency of occurrence, and activity of the esterase bands. There was no consistent trend in the number of bands relative to insecticide resistance. However, there was a trend in 5 of 6 scale stages tested for the insecticide-resistant population to exhibit higher esterase activity in band EST-3 compared with the susceptible population. When tested on the same cellulose acetate plate, insecticide-resistant, nongravid 3rd-instar females exhibited significantly greater esterase activity in band EST-3 compared with susceptible individuals. When staining duration was reduced from 45 to 5 min, fewer esterase bands were detected; however, the EST-3 band remained and showed even greater differentiation in activity between susceptible and resistant individuals. These data suggest that the EST-3 band is involved in insecticide resistance in California red scale and that the EST-3 band in nongravid 3rd-instar females could be used for a diagnostic test for resistance.

electrophoresis, armored scale, insecticide resistance, esterases