The invention provides transgenic plants and transformed host cells which express modified cry 3B genes with enhanced toxicity to Coleopteran insects. Also disclosed are methods of making and using these transgenic plants, methods of making recombinant host cells expressing these .delta.-endotoxins, and methods of killing insects such as Colorado potato beetle (Leptinotarsa decemlineata), southern corn rootworm (Diabrotica undecimpunctata howardi Barber) and western corn rootworm (Diabrotica virgifera virgifera LeConte.