Effects of photoperiod on developmental duration and reproduction of Sclerodermus alternatusi Yang (Hymenoptera: Bethylidae)

Sclerodermus alternatusi Yang, a newly discovered parasitic wasp of the genus Sclerodermus in China in recent years, was capable of parasitizing a variety of wood-boring pests in trees. Research indicate that photoperiod had a significant impact on the development and reproduction of parasitic wasps, yet its impact on S. alternatusi remains unreported. This study investigated the developmental duration and offspring quantity of S. alternatusi under four different photoperiods: 0 L∶24 D, 8 L∶16 D, 16 L∶8 D, and 24 L∶0 D. The results showed that the developmental durations of eggs, larvae, and pupae of S. alternatusi shortened as the length of light exposure increased. Under constant darkness (0 L∶24 D), all three developmental durations were the longest, while under continuous light (24 L∶0 D) they were the shortest. Specifically: egg duration differed by approximately 2 days, larval duration by about 4 days, and pupal duration by about 10 days. The total development time from egg to pupa varied by about 16 days. Photoperiod had a significant impact on the number of male offspring, with the fewest males under 24 L∶0 D photoperiod (averaging 1.4 males per tube), which was about 2.3 males per tube fewer than the maximum value observed. In contrast, the effect of photoperiod on the number of female offspring and total offspring was relatively small, ranging between 42 to 45 and 44 to 47 per tube, respectively. In all four treatments, S. alternatusi exhibited a typical female-biased sex ratio, with the proportion of females consistently above 90% and peaking at 97% under 24 L∶0 D photoperiod. The proportion of winged female offspring showed a trend of first increasing and then decreasing as the light exposure lengthened, peaking at 32.9% under 16 L∶8 D photoperiod and dropping to the lowest value of 5.1% under 0 L∶24 D. Under all photoperiods, the parasitism rate of S. alternatusi females on Thyestilla gebleri Faldermann larvae exceeded 85%, and the rate of offspring production exceeded 80%, with little variation across treatments. The above results indicated that when breeding S. alternatusi indoors, it was important to provide a suitable light condition. A photoperiod of 16 L∶8 D was optimal, as it not only significantly shortened the development duration of offspring but also maximized the proportion of winged females, which was beneficial for dispersal, while had a minimal effect on the total number of offspring.