Aldrin epoxidase activity and cytochrome P-450 content of microsomes prepared from alfalfa and cabbage looper larvae fed various plant diets

Abstract

The alfalfa looper ( Californica autographica) and the cabbage looper ( Trichoplusia ni) were reared through the fourth instar on a semidefined artificial diet and for the first 60 hr of the last instar on fresh leaves of one of their host plants. Microsomes prepared from midguts and a carcass segment which included the fat body were then assayed for aldrin epoxidase activity and cytochrome P-450 content. Epoxidation by midgut microsomes of alfalfa loopers fed peppermint leaves was at a rate up to eight times that of larvae fed alfalfa, snap beans, or broccoli. The epoxidase activity of the carcass microsomes was induced about fourfold by the peppermint diet. Midgut microsomes prepared from cabbage looper larvae reared on peppermint leaves were also more active (about four times) than those reared on alfalfa, broccoli, or cabbage. Although the epoxidase activity of the carcass microsomes of the cabbage loopers was low, about one-eighth that of the midgut microsomes, this enzyme was greatly induced by peppermint leaves. In neither species did the peppermint leaf diet cause a corresponding increase in the cytochrome P-450 content of the microsomes, the maximum difference between peppermint and the other plants being about twofold. Bioassays of cabbage looper larvae reared on broccoli or peppermint and of alfalfa loopers reared on alfalfa or peppermint indicated that the stimulation of microsomal oxidase activity by the peppermint constituents provided increased tolerance for carbaryl and methomyl but not acephate.