The sex- and developmental stage specific occurrence of gelatin-degrading enzymes has as yet never been systematically investigated in any insect species. By way of zymographic analysis, gelatinolytic activity was analyzed in the hemolymph and homogenates of the gray fleshfly Neobellieria bullata. Gelatinolytic activity was detected in feeding larvae and disappeared from both hemolymph and total body extracts during the wandering stage. An increase in gelatinolytic activity is observed around the third day after pupariation and again in lace pharate adults. In adult females, gelatinolytic activity is only present in the hemolymph during the vitellogenic stages, whereas it is undetectable in the adult male hemolymph. Gelatinolytic activity is high in the fat body of vitellogenic females but low in that of previtellogenic females and in males. Injection of 20-OH-ecdysone induces gelatinolytic activity in previtellogenic females and in liver-fed males. In vitro, this hormone triggers gelatinase production by the fat body of liver-fed males but surprisingly not by that of sugar-fed (previtellogenic) females, which indicates that ecdysteroids are not the only regulatory molecules involved. Our data suggest that in Neobellieria, and perhaps in other insects as well, gelatinolytic activity is indirectly involved in growth, metamorphosis and reproduction. (C) 1997 Elsevier Science Inc.