Effect of light energy on alkali-released virions from Anagrapha falcifera nucleopolyhedrovirus.

We compared the insecticidal activities of occluded and nonoccluded AfMNPV baculovirus obtained by dissolving the occlusion bodies (OB) with sodium carbonate. Droplet feeding and cotton leaf feeding bioassay techniques were used to determine the dose response against neonate Trichoplusia ni (Hübner) and loss of insecticidal activity when the virus was exposed to simulated sunlight from a xenon light source. Using droplet bioassays to determine a dose response, nonoccluded virus (NOV) was 20 times more active (LC(50) = 4.8 x 10(3) OB/ml, dissolved) than occluded virus (LC(50) = 9.6 x 10(4) OB/ml) when the samples remained wet. However, NOV lost activity when air dried before being tested by droplet (LC(50) > 1.0 x 10(6) OB/ml) or leaf feeding (LC(50) > 3.0 x 10(6) OB/ml) bioassays. Adding sucrose to NOV prevented the loss of insecticidal activity when samples were dried. The activity of NOV with 2% sucrose was similar to that of occluded virus samples, with or without sucrose, in both droplet feeding and leaf feeding assays. These results indicate that the OB protected the insecticidal activity of virions from the detrimental effects of drying. The OB also provided some protection from the detrimental effects of simulated sunlight (xenon) exposure. NOV samples exposed to xenon light had significantly greater loss of insecticidal activity than did similar samples of occluded virus. Without advancement in technologies, such as formulations, possible benefits of increased insecticidal activity from the use of nonoccluded virus is probably not sufficient to offset the rapid loss of activity due to drying or light exposure. Copyright 2000 Academic Press.