We have isolated a teratocyte secretory protein (TSP14) gene product from a hymenopteran endoparasite that disrupts the growth of lepidopteran insect larvae. To evaluate the insecticidal activity of TSP14 for the protection of crops from insect damage, chimeric gene constructs of TSP14 were expressed in transgenic plants. The coding sequence of the TSP14 gene, with and without its native signal peptide, was placed between the modified peanut chlorotic streak virus (PClSV) full-length transcript (FLt) promoter with duplicated enhancer domains and the terminator sequence from the rbcSE9 gene. These chimeric genes, expressed in transgenic tobacco (Nicotiana tabacum cv. Samsun NN) were stably inherited in successive plant generations (R0, R1 and R2 progeny) as shown by molecular analysis. A Western blot analysis of plant extracts showed the presence of a polypeptide of the expected size that cross-reacted with TSP14-specific antibodies. Larvae of the tobacco budworm (Heliothis virescens) and tobacco hornworm (Manduca sexta) which were fed with several independent homozygous transgenic plant lines (R2 progeny) exhibited mortality and reduced growth rates compared to those fed with plants transformed by a vector control. Our results demonstrate the potential for introduction of the TSP14 gene into plants in order to achieve protection against lepidopteran pests.