Abstract: Reproductive strategy of Sclerodermus alternatusi Yang, a parasitic wasp with a typical female-biased sex ratio, was investigated, focusing on the mating capacity of male wasps. The results showed that under four female-to-male ratios (15:1, 30:1, 60:1, and 90:1), the parasitism rate of S. alternatus all exceeded 95%. The pre-oviposition period of females showed little variation, averaging around 8.3 days. There were no significant differences in the egg duration, larval duration, pupal duration, or egg-to-pupal duration of the offspring. However, the number of female and male offspring varied significantly. At the 15:1 ratio, the number of female offspring was the highest, averaging 46.09 per host, while at the other three ratios, the female number decreased by about one-third. At the 15:1 ratio, the number of male offspring was the lowest, averaging only 2.47 per host, whereas it significantly increased to around 15 per host under the other three ratios. The total number of offspring did not vary significantly between the female-to-male ratios. The male offspring ratio showed significant differences, being lowest at 15:1 (average of 5.07%) and significantly increasing to 30%―40% in the other three ratios. At the 15:1 ratio, 96.55% of cases had a male offspring ratio below 10%, whereas under the other three ratios, most cases had a male offspring ratio above 20%. The study suggests that male S. alternatus can meet the sperm demand of approximately 15 females. Moreover, even at a female-to-male ratio exceeding 30:1, most females were still able to produce female offspring, indicating that the reproductive strategy of male wasps is to mate with as many females as possible rather than focusing on a few. However, the limited sperm provided by males resulted in a higher proportion of unfertilized eggs, leading to a significant increase in the male offspring ratio.

Key words: Sclerodermus alternatusi, parasitoid, brood size, male offspring rate, mating strategy