Responses of Arkansas populations of tarnished plant bugs (Heteroptera: Miridae) to insecticides, and tolerance differences between nymphs and adults

Tarnished plant bugs, Lygus linelaris (Palisot de Beauvois), collected from 4 sites in Arkansas were tested for susceptibility to 4 insecticides (λ-cyhalothrin, dimethoate, endosulfan, and oxamyl). Adults were subjected to vial bioassays. At LC 50 , 2 populations had higher tolerances to endosulfan than a susceptible reference; tolerance ratios (TR) were 33 and 36, respectively. These 2 populations were collected from cotton fields treated with multiple applications of insecticides in 1994. One of these populations also had significantly higher tolerance to oxamyl (tolerance ratio = 3.6) than the susceptible reference population. For all insecticides tested, LC 50 s were lower for the 2 populations collected during summer from unsprayed areas compared with the 2 populations collected during summer from areas treated with insecticides in 1994. Insecticide tolerances in insects from spring collections were lower than tolerances in summer-collected insects, except for insects collected from an area of low insecticide use. These differences were significant for 3 of the 4 insecticides-λ-cyhalothrin, endosulfan, and oxamyl-tested. In separate vial bioassays, we compared the insecticide tolerances of L. lineolaris nymphs and adults. At LC 50 , nymphs were significantly more tolerant (2.4-3.8 X) to all 4 insecticides.