The effect of age on sperm stock and egg laying in the parasitoid wasp, Dinarmus basalis

Sperm quantity and quality during storage may be constraints acting on female fecundity and hence fitness. In Hymenoptera, the importance of sperm quality has rarely been considered, despite its central role in reproductive strategies and especially in sex ratio control. In these insects, fertilized eggs develop into females and unfertilized eggs into males. Experiments were conducted on the female wasp, Dinarmus basalis, in the laboratory with and without egg-laying resources (hosts). The first point was to test if sperm age influenced sperm storage by measuring sperm count and viability using a sperm viability test (SYBR-14 : propidium iodide). The second point was the influence of prolonged storage in the female genital tract on the quantity, sex ratio and fitness of offspring produced. Results show that sperm viability in the spermatheca does not change significantly with maternal age, and that the sperm stock is not affected when females are deprived of hosts. Egg-laying is gradually restored after 21 days of host deprivation but remains at a low level after 115 days. The fitness of mated D. basalis females is therefore not constrained by sperm quantity or quality and seems to depend on host availability and female age.