STUDIES ON THE PERSISTENCE OF SPODOPTERA LITTORALIS NUCLEAR POLYHEDROSIS VIRUS ON COTTON IN EGYPT

Available from UMI in association with The British Library.; The persistence of a nuclear polyhedrosis virus infecting Spodoptera littoralis was investigated on cotton in Egypt. Viral infectivity was determined by bioassay and physical persistence of polyhedra on the crop by enzyme-linked immunosorbent assay. Highly purified virus was rapidly inactivated with little infective virus remaining on the plant after 4 days exposure. The factors determining virus persistence were inactivation by sunlight and physical loss of polyhedra from the plants, both effects were less on the more shaded areas of the plant. No inactivation resulted from the highly alkaline cotton leaf exudates, or field temperatures over an 8 day period.; Filtering sunlight showed that wavelengths between 300 and 320 nm caused most of the virus inactivation, and a calibration curve relating solar UV dose below 320 nm to the degree of virus inactivation was constructed. Several UV protectants were identified, specialized dyes were no more effective than molasses or clays and unpurified virus was as resistant to inactivation by sunlight as any of the formulations tested; this was attributed to the presence of insect homogenate in unpurified virus.; Significant physical loss occurred in the laboratory, but this was less than in the field where the loss was attributed to the abrasive action of wind and sand. Several gums and stickers were tested, none was completely effective in preventing physical loss and none of the formulations were more physically persistent than unpurified virus.; A 50% reduction in the amount of virus per unit area of leaf could result from growth dilution within one week.; Large differences occurred between the infectivity of virus fed to larvae on natural and artificial diets. This could not be attributed to antiviral chemicals and was probably related to palatability of the diets.