Effect of DIMBOA on growth and digestive physiology of Sesamia nonagrioides (Lepidoptera: noctuidae) larvae.

The hydroxamic acid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) was assessed for its effect on growth and digestive physiology of larvae of the stalk corn borer Sesamia nonagrioides Lef. Nutritional indices and activities of some digestive and detoxification enzymes were determined for larvae feeding on a DIMBOA-containing diet for the first two days of the third instar (short-term feeding assays), and from neonates to third instar (long-term feeding assays). DIMBOA reduced the relative growth rate and the efficiency of conversion of ingested food without affecting the relative consumption rate in long-term feeding assays, but it had no effect in short-term assays. Moreover, elastase-like activity was significantly increased by DIMBOA in short-term feeding assays, whereas microsomal oxidase activity was increased and esterase activity was reduced in long-term feeding assays. In vitro, DIMBOA inhibited the activities of carboxypeptidases, aminopeptidase, glutathione S-transferase and esterase, but it had no effect on trypsin, chymotrypsin and elastase. The implications of the altered levels of proteases and detoxification enzyme activities on the digestive physiology of larvae feeding on DIMBOA-containing diets are discussed.