BACILLUS-THURINGIENSIS ISOLATES FROM THE PHILIPPINES - HABITAT DISTRIBUTION, DELTA-ENDOTOXIN DIVERSITY, AND TOXICITY TO RICE STEM BORERS (LEPIDOPTERA, PYRALIDAE)

Bacillus thuringiensis Berliner isolates were detected in 57% of 801 s amples of rice grain dust, soil, rice field arthropods, and miscellane ous habitats (rice straw compost and mammal faeces) collected at 100 s ites in the Philippines. The collection yielded 3950 isolates of B. th uringiensis (8.7 isolates/positive sample). Grain dust from rice mills was the richest source (63% of the samples were positive, with 10.2 i solates/positive sample), followed by rice field arthropods, soil, and miscellaneous habitats. Polyclonal antibodies to six delta-endotoxin groups (Cry1A, Cry1B, Cry1C, Cry1D, Cry1E, and Cry3A) were used in enz yme-linked immunosorbent assays (ELISA) to characterize the toxins pro duced by each isolate. Subsamples of isolates representing the diversi ty of isolate sources and delta-endotoxin profiles were bioassayed aga inst the yellow stem borer, Scirpophaga incertulas (Walker) and stripe d stem borer, Chile suppressalis (Walker). Eighteen isolates highly to xic to both species were selected for characterization of delta-endoto xin genes by polymerase chain reaction (PCR) with primers specific to 14 genes or gene subfamilies, and Western blotting with Cry2A antibodi es. At least two novel delta-endotoxin genes, related to cry1B and cry 1F, were detected by DNA sequencing of PCR products.