The subject invention relates in part to the surprising and unexpected discovery that insects that are resistant to Bacillus thuringiensis Cry toxins have measurably altered alkaline phosphatase (ALP) activity as compared to insects that are susceptible to Cry toxins. This and other surprising discoveries reported herein have broad implications in areas such as managing and monitoring the development of insect resistance to B.t. toxins. For example, the subject invention provides a simple and fast assay (enzymatic or otherwise) for detecting ALP activity levels and thereby monitoring the development of resistance by insects to crystal protein insect toxins. There was no prior motivation or suggestion to go about resistance monitoring using this simple and easy approach.