| Summary: | Scarabaeoidea and Chrysomeloidea insects are agriculture-destructive coleopteran pests. Few effective <i>Bacillus thuringiensis</i> (Bt) insecticidal proteins against these species have been described. Bt isolate BtSU4 was found to be active against coleopteran insects. Genome sequencing revealed two new <i>cry8</i> genes in BtSU4, designated as <i>cry8Ha1</i> and <i>cry8Ia1</i>. Both genes expressed a 135 kDa protoxin forming irregular shape crystals. Bioassays performed with Cry8Ha1 protoxin showed that it was toxic to both larvae and adult stages of <i>Holotrichia parallela</i>, also to <i>Holotrichia oblita</i> adults and to <i>Anoplophora glabripennis</i> larvae, but was not toxic to larval stages of <i>H. oblita</i> or <i>Colaphellus bowringi</i>. The Cry8Ia1 protoxin only showed toxicity against <i>H. parallela</i> larvae. After activation with chymotrypsin, the Cry8Ha1 activated toxin lost its insecticidal activity against <i>H. oblita</i> adults and reduced its activity on <i>H. parallela</i> adults, but gained toxicity against <i>C. bowringi</i> larvae, a Chrysomeloidea insect pest that feeds on crucifer crops. The chymotrypsin activated Cry8Ia1 toxin did not show toxicity to any one of these insects. These data show that Cry8Ha1 and Cry8Ia1 protoxin and activated toxin proteins have differential toxicity to diverse coleopteran species, and that protoxin is a more robust protein for the control of coleopteran insects.
|
|---|
