RELATIVE TOXICITY OF NATIVE CHILEAN BACILLUS-THURINGIENSIS STRAINS AGAINST SCROBIPALPULOIDES ABSOLUTA (LEPIDOPTERA, GELECHIIDAE)

The larva of Scrobipalpuloides absoluta, a South American moth, is the most devastating insect pest of tomato production in Chile. The poten tial for using bacterial insecticides was studied analysing the relati ve toxicity of native Bacillus thuringiensis (BT) isolates belonging t o the Chilean collection. The polymerase chain reaction (PCR) techniqu e was used in order to facilitate the prescreening. Mixtures of homolo gous specific primers to regions within genes encoding CryI, CryIII an d CryIV crystal proteins were employed to generate a PCR product profi le of each BT isolate. Four isolates were selected and further charact erized by means of SDS-PAGE, Western blot and bioassays on fourth-inst ar S. absoluta larvae. Relative toxicities were evaluated by LD50 dete rminations. The entomocidal activity of isolate 121e, an autoagglutina ting strain, was threefold higher than toxin synthesized by B. thuring iensis var. kurstaki. This native strain was also active against Culex pipiens larvae, although much less than towards S. absoluta.