Fragments of Tenebrio molitor cadherin enhance Cry3Aa toxicity for the red flour beetle,Tribolium castaneum (Herbst)

Bacillus thuringiensis crystalline (Cry) proteins are highly toxic to a wide range of insect pests, but some species resist their action. This is true for many economically important beetles, including stored product pests, such as Tribolium castaneum. In this article, we show that the susceptibility of T. castaneum larvae to natural as well as to a recombinant Cry3Aa‐type toxin, applied in the diet, is enhanced by supplementing the diet with recombinant fragments of Tenebrio molitor cadherin; Cry toxin‐binding sites occur in several cadherin repeats (CR). In our study, we used the toxin‐binding region CRtb, which represents a substantial part of the repeat CR12‐MPED (membrane‐proximal extracellular domain). CRtb and CR12‐MPED consistently increased Cry3Aa toxicity. This synergistic effect occured at diverse mass ratios between the toxin and the cadherin fragments, suggesting that optimal ratios can be found. In our 6‐week‐long assay with T. castaneum, we achieved mortality of up to 96.6% with toxin concentration 30 μg/g. Cadherin fragments CR11 and CR9‐11 elicited small and diverse effects that require further analysis.