Physiological response of Colorado potato beetle and beet armyworm larvae to depletion of wound-inducible proteinase inhibitors in transgenic potato plants

Larvae of Colorado potato beetle (CPB), Leptinotarsa decemlineata, and beet armyworm (BAW), Spodoptera exigua, reared on potato plants in which wound- induced accumulation of proteinase inhibitors (PIs) was largely reduced thr ough antisense-mediated depletion of a specific lipoxygenase (LOX H3) had s ignificantly larger weight gains than those fed on non-transformed plants. The midgut endoproteolytic activities of CPB larvae fed on non transformed potato were significantly higher than those from larvae fed on LOX-H3-defic ient plants. However, none of these proteolytic activities was inhibited by potato leaf extracts, regardless of the plant that they were fed on. Taken together, these data suggest that CPB, a leaf-feeding specialist of solana ceous plants, is largely adapted to the inducible PIs of potato, though the metabolic cost associated with the hyperproduction of digestive proteases may account for the 14-31% lower weight gain of larvae fed on non-transform ed plants. The effect of LOX-H3 depletion on insect performance was more ev ident with larvae of the polyphagous BAW (52-63% higher weight gain and 73% higher fecundity when reared on LOX-H3-deficient plants). The poorer larva l performance of BAW on non-transformed plants may be due to the susceptibi lity to inhibition by potato leaf tissues of most BAW digestive proteases. Indeed, BAW larvae fed on non-transformed potato showed a significant reduc tion in most endoproteolytic activities compared to larvae fed on LOX-H3-de ficient plants, suggesting a that these insects deal poorly with induced pl ant defences in potato. (C) 2001 Elsevier Science Ltd. All rights reserved.