Laboratory, greenhouse and field studies were conducted to characterize the insecticidal properties of genetically altered forms of Autographa californica (Speyer) nucleopolyhedrovirus (AcNPV) and Helicoverpa zea (Boddie) NPV (HzNPV) against selected heliothine species. The altered viruses each contained a chimeric 0.8-kb fragment encoding the insect-specific, sodium channel neurotoxin from the Algerian scorpion, Androctonus australis Hector (AaIT, hence recombinant viruses designated Ac-AaIT and Hz-AaIT). Based on LD₅₀ values, results from diet-overlay bioassays showed Ac-AaIT and Hz-AaIT to be equally virulent against larval tobacco budworm, Heliothis virescens (F.), but HzNPV and Hz-AaIT averaged ~ 730-fold greater bioactivity than Ac-AaIT against larval cotton bollworm, Helicoverpa zea (Boddie). Hz-AaIT killed larvae of both heliothine species at rates significantly faster than those imparted by HzNPV (viral LT₅₀ values averaged 2.4 and 4.2 d, respectively). In greenhouse studies, foliar sprays of Ac-AaIT and Hz-AaIT were equally effective in controlling H. virescens on cotton, however, Hz-AaIT provided control of H. zea on cotton at a level superior to that of Ac-AaIT. For example, following 3 weekly sessions of foliar application and H. zea artificial infestation, cotton treated with Ac-AaIT or Hz-AaIT at 1 x 10¹² OB/ha averaged 2.5 and 16.2 non-damaged flower buds/plant, respectively. Additional greenhouse studies conducted against heliothine species on cotton showed that the quicker killing speed exhibited by Hz-AaIT led to improved plant protection versus HzNPV. Finally, results from one greenhouse and four field trials demonstrated that Hz-AaIT at 5 - 12 x 10¹¹ OB/ha provided control of the heliothine complex in cotton at levels Bacillus thuringiensis and only slightly less than that of select macrolide, pyrethroid and carbamate insecticides. Overall, results from these studies indicate that, due to host range differences between the two wild-type viruses, HzNPV is the better vectoring agent (versus AcNPV) for designing recombinant clones as insecticides targeted at the multi-species heliothine complex. Further, these studies suggest that, if appropriately tailored for the pest complex, recombinant NPVs may be very effective, insect-specific approaches to managing pests in many cropping scenarios. Possible Hz-AaIT deployment strategies for control of heliothine species on conventional and transgenic cotton varieties are discussed.