Lycotoxin I, from the wolf spider (Lycosa carolinensis), is an amphipathic pore-forming peptide that has antimicrobial and anti-insect activity. Constitutive expression of a lycotoxin I modified for oral toxicity to insects in tobacco (Nicotiana tabacum) conferred significantly enhanced resistance to larvae of the corn earworm (Helicoverpa zea) and cigarette beetle (Lasioderma serricorne). Gene expression levels of modified lycotoxin I were negatively correlated to the survival of corn earworm larvae. In addition, pathogenic symptoms caused by Pseudomonas syringae pathovar tabaci and Alternaria alternata on the modified lycotoxin I-expressing leaves were significantly less severe than on wild type leaves. These results indicate that modified lycotoxin I expression in tobacco can potentially protect leaf tissue from a broad spectrum of pests and pathogens.