BEHAVIOR OF PYRETHROID-SUSCEPTIBLE AND PYRETHROID-RESISTANT HELIOTHIS-VIRESCENS (F) (LEPIDOPTERA, NOCTUIDAE) LARVAE ON COTTON TREATED WITH INSECTICIDES

The behavior of a pyrethroid-resistant strain (R) and a-susceptible strain (S) of Heliothis virescens (F.) was observed on budding (flower buds) cotton plants in the greenhouse. Treatments were plants sprayed with (1) chlordimeform at the LC20 for the S strain; (2) cypermethrin at the LC20 for the S strain; (3) a mixture of chlordimeform and cypermethrin at the LC20 for the S strain (combined LC20s used in treatments 1 and 2); and (4) an unsprayed control. Third-stage R and S larvae were placed on the plants 1 h after spraying, and their behavior was recorded. Feeding of S larvae was reduced and resting was increased on plants treated with cypermethrin compared with R larvae, or S and R larvae on unsprayed plants. The chlordimeform treatment caused reduced feeding on flower buds and increased locomotion for S and R larvae compared with S and R larvae on untreated plants. The mixture of chlordimeform and cypermethrin significantly increased locomotion and reduced feeding of R larvae compared with their behavior on plants treated only with cypermethrin. Both S and R larvae abandoned plants treated with chlordimeform or the mixture more frequently compared with untreated or cypermethrin-treated plants. These results show that chlordimeform can alter behavior of S and R larvae on plants treated with cypermethrin. Under field conditions, use of behavioral active chemicals like chlordimeform could alter the behavior of wild H. virescens larvae so that flower bud damage is reduced and larval acquisition of insecticide residues is increased.