The present invention relates generally to modified Bacillus thuringiensis (Bt) insecticidal crystal proteins, also referred to as mutant toxins, with enhanced toxicity against a variety of insect genera, particularly mosquitos. The invention provides modified Bt Cry4Ba proteins, or mutant toxins, which have toxicity-enhancing sequence modifications at one or more positions within the amino acid sequence of the protein. The invention also provides polynucleotides encoding modified Cry4Ba proteins. The invention also provides insecticidal compositions comprising mutant toxins with a new or broadened insecticidal spectrum, and insecticidal compositions comprising polynucleotides encoding the modified Cry4Ba proteins.