Lycotoxin-1 peptide mutant peptides which exhibit increased insecticidal activity are produced by substitution of both a proline for the lysine at amino acid position 24 and a tryptophan for the leucine at amino acid position 25 of the wild-type amino acid sequence for lycotoxin-1. Further substitution of amino acids 8, 9 or 10 of the lycotoxin-1 wild-type amino acid sequence, specifically substituting a histidine for the phenylalanine at amino acid position 8, a glutamine for the glycine at amino acid position 10, or a serine for the leucine at amino acid position 9, provides an even greater increase in insecticidal activity. In addition to changes in the lycotoxin-1 amino acid sequence, the addition of an enterokinase K recognition site, DDDK, to the N-terminus of the lycotoxin-1 peptide increases insecticidal activity further still. Isolated nucleic acid sequences encoding the mutant lycotoxin-1 peptides, expression vectors containing these sequences, microorganisms or other host cells transformed with these vectors, and recombinant methods for producing the peptides, are also disclosed.