Temperature tolerance, thermal inactivation and ultraviolet light resistance of nuclear polyhedrosis virus of the armyworm, Mythimna separata (walk) (lepid.; noctuidae)

The nuclear polyhedrosis virus (NPV) of the armyworm, Mythimna separata, exposed to different temperatures and ultraviolet light (UV) was bioassayed on III instar larvae at 0.6 x 106 polyhedral inclusion bodies (PIBs)/larva. Based on the per cent larval mortality due to NPV, the infectivity of NPV as suspension at 11-500C up to 10 hr and as dry film at 500C up to 48 hr remained unchanged. At 72 hr, though more than 50% infectivity was observed, the infectivity of virus in the dry film lost significantly and at 96 hr it was almost nil. The NPV suspension subjected at 60-900C for 19 min indicated that the infectivity decreased as the temperature increased, and significantly so at 700C, followed by its complete absence at 900C. The ultraviolet light of wavelength 3130-4047 Angstroem, predominantly at 3130 and 3650 Angstroem has no adverse effect on the infectivity of NPV as suspension and dry film up to 4 and 12 hr respectively. At 24 hr the virus lost its infectivity significantly followed by complete loss at 72 hr. Further, no significant difference of resistance between suspension and dry film for the corresponding durations was observed. The other parameters like LT-50 values and incubation period showed no significant difference in all the experiments. Therefore, the armyworm NPV can survive the temperatures and UV light prevailing in the field and encourages its use as an agent for the biological control of the pest. (orig.)