EFFECT OF THE MAIZE-DERIVED COMPOUNDS DIMBOA AND MBOA ON GROWTH AND DIGESTIVE PROCESSES OF EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE)

The maize derived growth inhibitor, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), and one of its degradation products, 6-methoxybenzoxazolin-3-one (MBOA), were assessed for their mode of action on larvae of the European corn borer, Ostrinia nubilalis (Hubner). Nutritional indices computed for larvae administered the compounds in their diets showed that DIMBOA reduced the approximate digestibility of food and that MBOA reduced the efficiency of conversion of digested food. The results suggested that DIMBOA acts primarily as a digestive toxin and that the effects of MBOA occurred after digestion. Based on measurements of hydrolysis of artificial protease substrates, inclusion of DIMBOA or MBOA in diet ingested for 48 h or with crude gut homogenates reduced the activity of trypsin. Inclusion of DIMBOA decreased the activity of chymotrypsin on artificial substrates. DIMBOA inhibition of partially purified larval corn borer chymotrypsin was noncompetitive.