Cross Infectivity Effects of Environmental Factors on the Infectivity of Granulosis Virus of Phthorimaea operculella (Zeller) (Lepidoptera:Gelechiidae)

Studies on granulosis virus (GV) of Phthorimaea operculella (Zeller) were carried out to determine the LC₅₀, cross-infectivity and effect of sunlight, heat and rearing temperature on the infectivity. The LC₅₀ value of Phthorimaea operculella GV (PoGV) for the neonate larvae was 9.08 × 10⁴ occlusion bodies (Obs)/ml. The virus did not show cross-infectivity to other eleven lepidopterous insect species. The stability of GV was affected by sunlight, heat and rearing temperature. The virus could withstand exposure to sunlight for 4h without any significant loss of its infectivity. The infectivity gradually declined with increase in sunlight exposure period from 8 to 18h and total inactivation took place beyond 24h. The infectivity of PoGV was not affected significantly up to 40°C for 10 minutes exposure to heat and the thermal inactivation point (TIP) was in between 90 and 100 °C. Though the rearing temperatures of 20 to 35°C had no significant effect on infectivity of PoGV, rearing of the virus inoculated larvae of P. operculella at 25°C would be optimum for development of granulosis.