Effect of granulosis virus infection on food consumption and utilization by Pieris brassicae (Linnaeus)

The early fourth instar larvae of Pieris brassicae were fed on cabbage leaves treated with PbGV at three concentrations (2x10⁷, 1 x 10⁷ and 2 x 10⁶ occlusion bodies ml⁻¹) to ascertion the food consumption and its utilization by P. brassicae larvae upon infection under laboratory conditions. It was found that the mean consumption index decreased to the tune of 4.39% at 24 hours to 67.19% at 120 hours over control after PbGV infection. Approximate digestibility also reduced from 4.22 to 80.78% at 24 and 120 hours, respectively over control. Food consumption of virus-treated larvae decreased with passage of time as compared to the healthy larvae. Conversion of ingested and digested food to body substance also reduced in virus infected larvae to different degrees which ranged from 2.77 to 96.04% for ingested food and 4.55 to 92.16% for digested food. The differences among various concentrations with respect to consumption index, approximate digestibility, conversion of ingested and digested food were, however, statistically non-significant. The impact of virus infection on food consumption and utilization by P. brassicae larvae was enhanced with time after infection.