Coleopteran cadherin fragments synergize toxicity of Bacillus thurigiensis toxins, Cry3Aa, Cry3Bb, and Cry8Ca, against Alphitobius diaperinus (Coleoptera: Tenebrionidae) larvae

The lesser mealworm (LMW), Alphitobius diaperinus, is a serious cosmopolitan pest of stored product and commercial poultry facilities because of its involvement in structural damage to poultry houses and transfer of avian and human pathogens. Cry3Aa, Cry3Bb, and Cry8Ca insecticidal proteins of Bacillus thuringiensis are used to control of coleopteran larvae. Cadherins localized in the midgut epithelium function as receptors for Cry toxins in lepidopteran and dipteran insects. Previously, we demonstrated that the truncated cadherin (DvCad1) from Diabrotica virgifera virgifera, which consists of the C-terminal cadherin repeats (CR) 8 to 10 and expressed in Escherichia coli, enhanced Cry3Aa and Cry3Bb toxicity against several coleopteran species. Here we report that the TmCad1, which contains CR 12 to membrane proximal extracellular domain (MPED) from cadherin of Tenebrio molitor and expressed in E. coli, DvCad1 binds toxin and enhances Cry toxicity to LMW larvae. By an enzyme linked immunosorbent microplate assay, we demonstrated that the DvCad1 not only binds activated-Cry3Aa (11.8 nM), -Cry3Bb (1.4 nM), and -Cry8Ca (7.1 nM) toxins, but TmCad1 also binds activated-Cry3Aa (15.4 nM), -Cry3Bb (13.0 nM), and -Cry8Ca (5.9 nM) with high affinity. LMW larvae feeding on DvCad1 and TmCad1 had increased susceptibility to Cry3Aa, Cry3Bb, and Cry8Ca toxin. The extent of Cry toxins enhancement by DvCad1 and TmCad1, which ranged from 2.28- to 13.1-fold, may have practical application for LMW control in preventing avian and human pathogens in poultry facility.