Induction of microsomal oxidases by host plants in the fall armyworm, Spodoptera frugiperda (J. E. Smith)

Abstract

Larvae of the fall armyworm ( Spodoptera frugiperda (J. E. Smith)) were maintained on a semidefined artificial diet until the end of the fifth instar and the newly molted sixth-instar larvae were then fed fresh leaves of various host plants for 2 days prior to microsomal oxidase assays. The order of the midgut aldrin epoxidase activity of larvae after feeding on these plants was: corn > Bermuda grass > cotton > cowpeas > cabbage > peanuts > sorghum > alfalfa > millet > soybean. The ratios of aldrin epoxidase, p-nitroanisole O-demethylase, and p-chloro- N-methylaniline N-demethylase activities for soybean- and corn-fed larvae were 4.5, 6.3, and 2.7-fold, respectively. The induction was affected by the age and developmental stage of the corn plant with mature leaves from old plants being more active. Higher epoxidase activities were also observed in mature larvae reared on corn plants since egg stage as compared with those on soybean plants. Monoterpenes such as α-pinene, β-pinene, limonene, menthol, and peppermint oil were found to induce the midgut epoxidase activity. Corn-fed larvae were more tolerant of the insecticides methomyl, acephate, methamidophos, diazinon, trichlorfon, monocrotophos, permethrin, and cypermethrin than soybean-fed larvae.