• Apyrene;
  • eupyrene;
  • granulovirus;
  • pathogen;
  • sub-lethal

1. A dose-dependent decrease in male fertility occurs in the Indian Meal Moth, Plodia interpunctella, when sub-lethally infected with granulovirus during the larval stage.

2. Here, the causes for this decline are investigated by examining eupyrene and apyrene sperm numbers and sizes produced by males across four levels of viral challenge.

3. The results could not explain how reduced male fertility is caused in this host–pathogen interaction. While a reduction in both eupyrene and apyrene sperm numbers from all virus-treated males was found, this was not significant and neither was there a difference in sperm lengths across the four treatments. There were also no differences in the variances of sperm numbers or lengths between the doses, and no associations between sperm numbers or lengths and body size were found.

4. A significant correlation between eupyrene and apyrene numbers was found, but this was independent of dose. Significant between-male variance in apyrene sperm lengths was found, indicating that individual males differ in the range of apyrene sperm sizes they produce.

5. It is suggested that further intracellular and behavioural study is needed to identify the causes of the granulovirus-induced reduction in fertility of P. interpunctella.