Effect of parasitoid density on the timing of parasitism and development duration of progeny in Sclerodermus pupariae (Hymenoptera: Bethylidae)

The gregarious idiobiont ectoparasitoid, Sclerodermus pupariae Yang et Yao, is a natural enemy that parasitizes buprestid and cerambycid beetle larvae in China. In a recent laboratory study of mass–reared female parasitoids on larvae of the substitute host, Thyestilla gebleri, the subsequent offspring were widely released to control target pests. To develop cost–effective techniques for rearing parasitoids, and improve the parasitic efficiency of Sclerodermus pupariae, several parasitoid–host ratios have been investigated. However, the mechanism whereby increasing the density of inoculated female wasps on a host affects female parasitoid fitness (adult performance and progeny developmental duration) remains unclear. In the present study, we examined the influence of parasitoid density (one to eight female wasps per host) on the time to first attack, paralyzing time, pre–oviposition period and oviposition period of foundresses and developmental duration of offspring. We showed that the time to first attack, paralyzing time, pre–oviposition period and oviposition period of foundresses were significantly negatively associated with parasitoid density, but that developmental duration of progeny was only affected at the larval stage. An increase in the parasitoid density to more than three female wasps per host had no significant influence on the investigated parameters. Our results suggest that host nutrition was adequate, and intraspecific interaction enhanced the parasitic efficiency of wasps sharing a single host. Furthermore, it is known that a suitable parasitoid–host ratio can play an important role in promoting mutually beneficial behaviors which enhance adult performance.