SYNERGISTIC ACTIVITY OF A BACILLUS-THURINGIENSIS DELTA-ENDOTOXIN AND A BACTERIAL ENDOCHITINASE AGAINST SPODOPTERA-LITTORALIS LARVAE

In an attempt to increase the insecticidal effect of the delta-endotox in crystal protein CryIC on the relatively Cry-insensitive larvae of S podoptera littoralis, a combination of CryIC and endochitinase was use d. CryIC comprising the first 756 amino acids from Bacillus thuringien sis K26-21 and endochitinase ChiAII encoded by Serratia marcescens wer e separately produced in Escherichia coli carrying the genes in overex pression vectors. The endochitinase on its own, even at very low conce ntrations (0.1 mu g/ml), perforated the larval midgut peritrophic memb rane. When applied together with low concentrations of CryIC, a synerg istic toxic effect was obtained. In the absence of chitinase, about 20 mu g of CryIC per ml was required to obtain maximal reduction in larv al weight, while only 3.0 mu g of CryIC per mi caused a similar toxic effect in the presence of endochitinase. Thus, a combination of the Cr y protein and an endochitinase could result in effective insect contro l in transgenic systems in which the Cry protein is not expressed in a crystalline form.