Dietary stress reduces the susceptibility of Plodia interpunctella to infection by a granulovirus

To investigate the hypothesis that dietary stress can result in the increased susceptibility of insects to pathogens Plodia interpunctella larvae were dosed with the granulovirus of P. interpunctella (PiGV), whilst feeding on a high or low quality diet. Control larvae on the high quality diet had a significantly higher rate of survival to pupation (63.6%) than larvae on the low quality diet (44.4%). Of the larvae dosed with virus, those feeding on the high quality diet were more susceptible to infection than those fed a low quality diet, having significantly lower LD50 values. The LD50 (log) value was 3.232 capsules/larva for the high quality diet and 5.936 capsules/larva for the low quality diet. Once infected with the virus, larvae on the high quality diet survived longer (21 days) than those on the low quality diet (15 days), having significantly higher LT50 values. These results suggest that dietary stress does not automatically make P. interpunctella more susceptible to infection by pathogens but has a more complex effect.