The subject invention pertains to the use of peptide fragments of cadherins (including cadherin-like proteins). The subject invention includes a cell (and use thereof) comprising a polynucleotide that expresses the peptide fragment. The subject invention includes methods of feeding the peptides to insects. In preferred embodiments, the peptides are fed to target insects together with one or more insecticidal proteins, preferably (but not limited to) B.t. Cry proteins. When used in this manner, the peptide fragment can not only enhance the apparent toxin activity of the Cry protein against the insect species that was the source of the receptor but also against other insect species. Preferably, the cadherin is a Bacillus thuringiensis (B.t.) insecticidal crystal protein (Cry) toxin receptor. Preferably, the peptide fragment is a binding domain of the receptor. In some preferred embodiments, the peptide is the binding domain nearest to the membrane proximal ectodomain. Corresponding domains are identifiable in a variety of B.t. toxin receptors.