Microplitis croceipes is a Braconid endoparasitoid that uses the secretion of factors expressed after parasitization from teratocytes to suppress its primary host Heliothis virescens from developing at a normal rate. Teratocytes are cells the line the serosal membrane of the developing endoparasitoid larvae that slouth off into host hemolymph during the first twenty-four hours of parasitization. Purified teratocyte secretory protein 14 (TSP14) has been shown to inhibit translation in vitro using a testicular bioassay, and repress growth and development of H.virescens larvae that ingested it with artificial diet. Feeding bioassays performed in greenhouse with transgenic tobacco plants expressing TSP14 has been shown to increase mortality, slowed growth and development, and cause larvae-pupal intermediates of H.virescens and nontarget host Manduca sexta larvae that feed on these transgenic lines. Lines TSP14 118 (1) R1 #5 (with signal peptide), and TSP14 117 (3) R1 #1 (without signal peptide), showed most prominent effect on alterations of larval development and caused highest rates of mortality in greenhouse study, therefore based on these results we used these transgenic lines in 2003 field trial. During the initial field trial trends for suppression of Epitrix hirtipennis (tobacco flea beetle), and Myzus nicotianae (tobacco aphid) populations were noted, as well as an increase of parasitism of M.sexta larvae consuming TSP14 expressing tobacco plant lines was observed. In second field season we investigate if these trends were based on the insecticidal activity of TSP14, or a result of other environmental factors.