Cecropins are produced by insects, particularly under conditions of infection. Cecropins are bioactive peptides that interact with membranes and form transmembrane channels that allow the free flow of electrolytes, metabolites, and water across the phospholipid bilayers. Anti-cecropin B is useful for the detection of cecropin B in various immunological assays. Cecropin B has been modified in some instances by substituting a single amino acid to render the molecule less susceptible to proteolytic cleavage.