Polarized Ketone Inhibition of 1-Naphthyl Acetate Esterase in Azinphosmethyl-Resistant and -Susceptible Tufted Apple Bud Moths, Platynota idaeusalis (Walker): Novel Insecticide Synergists

Aliphatic and aromatic polarized trifluoromethyiketones were synthesized as inhibitors of l-naphthyl acetate (NA) esterase and potential insecticide synergists for azinphosmethyl-resistant tufted apple bud moths. A 1 -NA resistance-associated esterase (RAH) was isolated from whole body homogenates of azinphosmethylresistant adult females. A second susceptible-associated I-NA esterase (SE) was purified from azinphosmethyl-susceptible adult females of the tufted apple bud moth. In structure-activity studies, octylthio-1,1,1trifluoromethyl-2-propanone (OTFP) was the most potent inhibitor of whole body I-NA esterase from resistant and susceptible adult females. The I50s for inhibition of purified RAE and SE were 1 X 10^8.5 and I X 10^8.6 M, respectively. Longer and shorter n-alkyl groups or a S-phenyl substitution reduced inhibitory activity. These inhibitors were also found to compete with I-NA substrate for the esteratic active site. OTFP alone had minimal toxicity toward third and fifth instars of the tufted apple bud moth but synergized azinphosmethyl toxicity in resistant insects. Although novel esterases were found in resistant bud moth larvae and adults, there was no evidence that the resistance-associated esterases had a unique function different from that found in susceptible insects.