PERSISTENCE AND EFFICACY OF 4 NUCLEAR POLYHEDROSIS VIRUSES FOR CORN-EARWORM (LEPIDOPTERA, NOCTUIDAE) ON HEADING GRAIN-SORGHUM

The persistence and efficacy of Helicoverpa zea nuclear polyhedrosis v irus (HzNPV) on heading grain sorghum was compared with three multiply -enveloped NPVs from other hosts to which the corn earworm, Helicoverp a zea (Boddie), is susceptible. Bioassay of NPV by feeding florets fro m sprayed heads to second instar corn earworm showed only low levels o f virus remaining on heads in all of the treatments four days after ap plication. The initial activity and persistence of a commercial prepar ation of H. zea NPV were greater than four unformulated virus preparat ions including unformulated HzNPV at rates of 3, 6, and 15 X 10(11) po lyhedral inclusion bodies (PIB) per ml (P < 0.05). Initial activity an d persistence were similar for unformulated preparations of HzNPV, Hel iothis armigera (HaNPV), and Autographa californica (AcNPV). Activity and persistence of Anticarsia gemmatalis (AgNPV) were significantly le ss than for the other viruses (P < 0.05). In a small plot test on head ing grain sorghum in which viruses were applied at 1.5, 3, and 6 X 10( 11) PIB/ha, mortality of collected corn earworm larvae and larval popu lation reduction were greater in the HzNPV treatments than in the thre e multiply-enveloped virus treatments. HaNPV and AcNPV preparations we re more effective than AgNPV. All virus preparations required one wk o r longer to significantly reduce larval populations at all rates (P < 0.05).