A series of laboratory, greenhouse and field studies were conducted to characterize the biological activity of a recombinant form of Autographa californica nuclear polyhedrosis virus (AcNPV). The recombinant NPV (vEGTDEL/AaIT) had a deletion in the ecdysteroid UDP-glucosyltransferase gene and carried a synthetic copy of a gene encoding expression of an insect-selective neurotoxin, AaHIT, which was isolated from the scorpion Androctonus australis Hector. Based on LT50 values obtained in treated artificial diet assays, vEGTDEL/AaIT controlled larvae of Heliothis virescens, Trichoplusia ni and Helicoverpa zea at rates of 96%, 51% and 2.6-fold faster than AcNPV, respectively. Results from a greenhouse study conducted against H. virescens on cotton showed that hastened speed of action exhibited by the gene-inserted NPV does indeed lead to improved plant protection. For example, following six foliar applications and artificial pest infestation sessions, cotton treated with equal doses of AcNPV or vEGTDEL/ AaIT averaged 46.9 and 18.9% damaged flower buds, respectively (untreated cotton had 68.9% damaged buds). When applied to field-grown cotton at equivalent rates of 2 x 1012 polyhedra/ha, vEGTDEL/AaIT controlled both H. virescens and H. zea significantly faster than a non-AaIT form of AcNPV. At three days posttreatment, vEGTDEL/AaIT and non-AaIT AcNPV caused 94.5 and 58.2% mortality in H. virescens, and 53.5 and 2.0% mortality in H. zea, respectively. Surveys of cotton plots over the duration of this field study showed that weekly applications of vEGTDEL/AaIT had no adverse effects on population densities of non-target arthorpods, with species representing 18 different non-lepidopteran families being found at the test site.