SYNERGISM OF INSECTICIDES AGAINST SUSCEPTIBLE AND PYRETHROID-RESISTANT TOBACCO BUDWORMS (LEPIDOPTERA, NOCTUIDAE) BY AMITRAZ

The synergistic activity of amitraz was examined in laboratory tests with neonate-susceptible and pyrethroid-resistant tobacco budworms, Heliothis virescens (F.). Synergism occurred with both strains and was greater with resistant neonates. Addition of piperonyl butoxide increased synergism in both strains; a greater increase occurred in the resistant strain. SN 49484 base (N'-[2,4-dimethylphenyl]-N-methylformamidine), the probable active metabolite of amitraz, was similar to amitraz in synergistic activity. A 1:1 mixture of amitraz-SN 49844 was more synergistic than either formamidine alone. Field tests demonstrated synergism of cypermethrin and an acephate-endosulfan combination by amitraz against H. virescens larvae in cotton plant terminals. A mixture of cypermethrin with amitraz and piperonyl butoxide was synergistic late in the cotton growth season when pyrethroid resistance was widespread in field populations of tobacco budworms.