New Isolates of Bacillus thuringiensis for Control of Livestock Ectoparasites

Buffalo fly (Haematobia irritans exigua), sheep blowfly (Lucilia cuprina), and the sheep body louse (Bovicola ovis) are important pests of the Australian livestock industry. Current control measures rely heavily on chemical insecticides. Because all three pests have developed resistance and insecticide residues in animal products threaten trade, alternative control strategies need to be investigated. The bacterium, Bacillus thuringiensis (Bt), produces protein (δ-endotoxin) crystals that are specifically toxic to some insects. In this study, feeding assays were used to screen Bt isolates for toxicity to adult and larval buffalo fly, larval sheep blowfly, and adults and nymphs of the sheep louse. Some Bt isolates were found to have high toxic activity against larvae of the two fly species and moderate activity against the sheep louse. This is the first report of insecticidal activity of Bt toxin against buffalo fly. Bacillus thuringiensis isolates with toxic activity due to δ-endotoxin were characterized further by polymerase chain reaction to identify toxin genes. In four isolates, no cry genes were identified with the primer sets used. These isolates were analyzed further by amino-terminal sequencing of the protein bands. Two amino acid sequences, unrelated to any known Cry proteins, have been identified by database searches.