THE EFFECT OF NATURAL SUNLIGHT ON SPODOPTERA-LITTORALIS NUCLEAR POLYHEDROSIS-VIRUS

The effect of natural sunlight on Spodoptera littoralis (Boisduval) nuclear polyhedrosis virus (NPV) in Egypt was investigated. Wavelengths between 300 and 320 nm were shown to be responsible for almost all of the inactivation attributed to sunlight, although there was some deleterious effect of wavelengths between 320 and 400 nm and above 665 nm. When NPV was exposed to wavelengths between 400 and 665 nm in addition to wavelengths above 665 nm, no inactivation occurred. A simple linear regression equation relating solar UV dose below 320 nm to inactivation of NPV was obtained based on several experiments carried out over a 4-year period. The survival curve follows the pattern of a single-hit, single-target model. The relationship also could be described as a bisegmented curve and it was concluded that this might be due to a proportion of the virus being inherently more stable to inactivation by sunlight or that two reactions are involved in the inactivation process.