CARBOXYLAMIDASE ACTIVITY IN THE FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE) AND OTHER LEPIDOPTERA, ORTHOPTERA, AND DICTYOPTERA

Carboxylamidase activity in larvae of the the fall armyworm, Spodopter a frugiperda (J. E. Smith),was studied using p-nitroacetanilide as a m odel substrate. Enzyme activity was found in all tissues examined, wit h the midgut exhibiting the highest specific activity. Of the midgut s ubcellular fractions, the microsomal fraction contained. the highest s pecific activity. The apparent K-m value for the enzyme was 0.67 mM an d the DH optimum was 8.0. The enzyme was quite stable, losing <10% of its original activity after 10 wk at -20 degrees C. Activity was inhib ited in vitro by the hydrolase inhibitors paraoxon, triphenyl phosphat e, eserine, and phenylmethylsulfonyl fluoride, showing I-50 values Of 2.8 mu M, 0.19 mM, 24 mu M, and 0.13 mM, respectively. Activity was al so inhibited by several organophosphorus insecticides at 0.1 mM; profe nofos inhibited the enzyme 93%, dichlorvos 94%, and tetrachlorvinphos 75%. Carboxylamidase activity was ex-pressed in all postembryonic stag es. It was widely distributed in different insect species from the ord ers Lepidoptera, Orthoptera, and. Dictyoptera. In the cockroach specie s studied, activity appeared to be family dependent. Activity was high est among the Blattellidae, intermediate among the Blaberidae, and not detectable in the Blattidae. Carboxylamidase activity toward other ar omatic amides such as acetanilide and phenacetin was also detected in fall armyworm larvae.