Egg production by the mermithid nematode Strelkovimermis spiculatus, a parasite of mosquitoes, was examined over a period of 34 days. Oviposition did not occur in the absence of males. Egg production was best when males were continuously present (6.4 x 10(3) +/- 0.9 x 10(3) eggs/female). Fewer eggs were produced when males were removed after 7 days (2.8 x 10(3) +/- 0.2 x 10(3) eggs/female) and oviposition partially recovered after males were returned 11 days later (4.4 x 10(3) +/- 0.5 x 10(3) eggs/female). The nematodes deposited substantially more eggs in sand (6.4 x 10(3) +/- 0.9 x 10(3)/female) than in water (1.9 x 10(3) +/- 0.3 x 10(3)/(female).