A comparative evaluation of the susceptibility to insecticides and detoxifying enzyme activities in Stethorus gilvifrons (Coleoptera: Coccinellidae) and Panonychus ulmi (Acarina: Tetranychidae)

Abstract

The ladybird beetle Stethorus gilvifrons (Muls.) does not provide sufficient mite control in many of the apple orchards in Bursa, despite being an effective and voracious predator of the European red mite, Panonychus ulmi (Koch). This is due in large part to a heavy dependency on organophosphate (OP) and synthetic pyrethroid (SP) insecticides, which were applied to target key pests. To help understand the effects of the insecticides on the ladybird beetle and its main prey, P. ulmi, this study aims to determine their susceptibilities to the residues of parathion-methyl and bifenthrin and detoxifying enzyme activities, such as carboxylesterase (CarE) and glutathione S-transferase (GST). In addition, the insensitivity of acetylcholineesterase (AChE) to the inhibitors, paraoxon and primicarb, is also determined. There are differences in susceptibility to parathion-methyl, in CarE activity and AChE insensitivity, among the populations of predator ladybird and the spider mite. Although GST might play an important role in detoxifying OPs, there is no relationship between susceptibility to parathion-methyl and bifenthrin and GST activity in both the ladybird and the spider mite. On the other hand, two S. gilvifrons populations were surprisingly tolerant to two insecticides. The disparity in susceptibility to parathion-methyl among the predator populations was due to the responsibility of multiple biochemical resistance mechanisms, including elevated CarE activity and target-site insensitivity. Furthermore, the tolerance of the two populations of ladybirds to bifenthrin was similar to that of two P. ulmi populations collected from the same orchards, which indicates a coadaptation to SPs. Therefore, enhanced detoxification by increased activity of CarE is largely responsible for the observed tolerance to bifenthrin in S. gilvifrons populations. Consequently, these results demonstrate that the ladybird species tend to develop resistance to insecticides in the field.