Effects of viral rate and feeding time on mortality of early-, mid-, and late-stadium larvae of Helicoverpa zea (Lepidoptera: Noctuidae) fed Baculovirus heliothis

抄録

Early-, mid-, and late-stadium Helicoverpa zea larvae were fed on a diet which was surface-treated with occlusion bodies (OB) at rates from 0.1 to 1, 000 OB/mm² for periods ranging from 0.25 to 72 h. Fifty-percent of early-stadium larvae fed 0.1, 1, 10, and 100 OB/mm² eventually died after they had fed for 7.5, 4.5, 2.3, and 0.3 h, respectively, and then were transferred to virus-free diet. Greater than 98% mortality occurred, regardless of the viral rate, after 24 h of feeding. Less than 0.5 h of feeding at the highest rate (1, 000 OB/mm²) resulted in 100% mortality. Using mid-stadium larvae, 50% mortality at 0.1, 1, or 10 OB/mm² occurred when larvae had fed for 11.0, 3.5 or 0.3 h, respectively, and then were transferred to virus-free diet. Viral rates of 100 or 1, 000 OB/mm² resulted in >90% mortality after only 0.25 h of feeding. All mid-stadium larvae fed the highest rates (10, 100 or 1, 000 OB/mm²) for at least 12 h and then transferred to virus-free diet, eventually died of a virus infection. One-hundred percent mortality, however, was never reached when larvae were fed for 72 h at the two lowest rates of 0.1 and 1.0 OB/mm². Within each viral rate it did not seem to matter whether late-stadium larvae had fed for 1 or 72 h on virus-treated diet. Mortality of late-stadium larvae was never greater than 75% regardless of the viral rate or feeding time. Mortality of early-, mid-, or late-stadium larvae not fed virus never exceeded 2%.