DIET-RELATED PLASTICITY OF THE DIGESTIVE PROTEOLYTIC SYSTEM IN LARVAEOF THE COLORADO POTATO BEETLE (LEPTINOTARSA-DECEMLINEATA SAY)

Quantitative and qualitative changes in digestive proteolytic activiti es were monitored in fourth-instar larvae of the Colorado potato beetl e (Leptinotarsa decemlineata Say) subjected to three different leaf di ets. Depending on the diet, the larvae exhibited variable growth rates , similar for potato (Solanum tuberosum) and eggplant (Solanum melonge na) diets but lower for the tomato (Lycopersicon esculentum) diet. Int erestingly, these growth rates were not associated with total protease activity in the midgut. While growth of tomato-fed insects was neglig ible, midgut protease activity in these insects was 1.5 and 4.2 times higher than that measured for potato-and eggplant-fed insects, respect ively. As seen on gelatin-containing polyacrylamide gels, midgut extra cts from insects that ingested eggplant leaves contained only a few pr oteinase forms, while numerous forms were observed in extracts of pota to-and tomato-fed larvae. Although several forms were common to the th ree diets, their relative importance in the insect midgut varied. This diet-related plasticity of the digestive proteolytic system in Colora do potato beetle larvae leads one to question the potential for contro l approaches based on the inhibition of digestive proteases. (C) 1997 Wiley-Liss, Inc.