Investigations on the comparative ultraviolet photobiology of representative insect viruses of the genera Baculovirus and Iridovirus

The effects of ultraviolet radiation on the nuclear polyhedrosis virus (NPV) (Baculovirus) of Galleria mellonella (Lepidoptera: Pyralidae), the NPV of Autographa californica (Lepidoptera: Noctuidae), the granulosis virus of Laspeyresia pomonella (Lepidoptera: Olethreutidae), the iridescent virus (Iridovirus) of Tipula sp. (Diptera: Tipulidae), the iridescent virus of Chilo sp. (Lepidoptera: Pyralidae) and the iridescent virus of Sericesthis sp. (Coleoptera: Scarabaeidae) were studied. For a source of far ultraviolet radiation (lambda = 253.7 nm), two 15 watt germicidal lamps were used; for a source of near ultraviolet radiation (lambda = 300-380 nm), two 15 watt black lights were used. Virus inactivation was assessed by bioassay with insect larvae and by plaque assay with cultured insect cells. Ultraviolet inactivation data was analyzed with probit techniques. For NPV's nucleocapsids were inactivated in a similar manner when assayed in host larvae or by plaque assay in cultured cell monolayers. NPV polyhedra were inactivated after exposure to far uv at a rate similar to that for nucleocapsids suggesting that polyhedra do not effectively protect nucleocapsids from the action of far uv. Inactivation of Baculovirus infectious forms and of Iridovirus nucleocapsids occurred after lengthy exposure to near uv. In general, the near uv dose required to inactivate 50% of the experimental preparations was at least 100 times and often 1000 times greater than that required for an equivalent amount of inactivation by far uv. For NPV nucleocapsids inactivation of 50% of virus preparations occurred after 10 hrs irradiation, whereas 50% of the irradiated polyhedra preparations were inactivated after 24 hrs irradiation