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On grain sorghum, fifth and later instars offfeliothis armigera caused practically all observed damage to ovaries, i.e. damage responsible for yield loss. By contrast, early instars fed almost exclusively on anthers. The early preference for anthers and synchrony of larvae and sorghum head development indicate that larvae of H. armigera would be highly susceptible to larvicides timed at 100% anthesis.

The potencies of 10 strains (seven subspecies) of Bacillus thuringiensis for Helicoverpa armigera and H. punctigera were compared using a droplet-feeding method. Larvae were attracted to petri dishes for dosing using a light-proof box, and imbibed the bacteria in droplets sprayed onto the dishes. The strains displayed a 300-fold difference in potency for H . armigera and 750-fold difference for H. punctigera. Two strains were equal to the commercial strain (subspecies kurstaki, serotype 3a3b) in potency against H. armigera, namely subspecies kenyoe, serotype 4a4c and aizawai, serotype 7; and one, kenyae, serotype 4a&, was also similar to the commercial strain against H. punctigera. The strains ranked simiiarly in potency against H. armigera and H . punctigera, suggesting that screening for potency against both Helicoverpa spp. can be accomplished by testing against only one of the species.