Susceptibility to acaricides and detoxifying enzyme activities in the red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae)

Susceptibility of red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae), collected from conventionally-managed (synthetic acaricide usage) versus an organicallymanaged (no acaricide usage) tea plantations in Assam, India, to five synthetic acaricides was determined in laboratory bioassays. Activity of three principal detoxifying enzymes of these mite populations was also assayed. The median lethal concentrations (LC50) of ethion, dicofol, propargite, fenpropathrin, and fenazaquin were 1049.75, 599.21, 232.03, 11.44, and 6.75 ppm, respectively. Field rates of these acaricides were compared with 95% lethal concentration (LC95 in ppm) values, and a decrease in the susceptibility of the test population to ethion, propargite, dicofol and fenpropathrin was observed. There was no change for fenazaquin which was effective at lower doses than the recommended dose. Of all the acaricides tested, fenazaquin was the most toxic and ethion was the least toxic. General esterases (GEs), glutathione- S-transferase (GST), and cytochrome P450 monooxygenases exhibited a higher activity in mite population from the conventionallymanaged tea plantation as compared with the activity in mites from the organicallymanaged tea plantation. These findings may be helpful in the selection of acaricides and in developing resistance management strategies for an effective management program for this major tea pest.