Optimal inoculation density of Dastarcus longulus (Coleoptera:Bothrideridae) larvae for rearing on pupae of Zophobas atratus (Coleoptera:Tenebrionidae)

The ectoparasitoid Dastarcus longulus Sharp (Coleoptera:Bothrideridae) is considered a potent natural enemy of Monochamus alternatus Hope (Coleoptera:Cerambycidae) and other cerambycid beetles. Our previous study highlighted the effectiveness of using once-frozen Zophobas atratus (Coleoptera:Tenebrionidae) pupae as a substitute host for mass rearing of D. longulus, although problems such as low parasitic success rates and small offspring size persist. To address these problems, our study focused on determining the optimal inoculation density of D. longulus larvae for rearing on pupae of Z. atratus. When 5, 10, 20, and 30 D. longulus larvae were inoculated per host, the rate of successful parasitism and pupal body size decreased with higher larval densities. Furthermore, intraspecific competition did not affect the fresh weight of D. longulus pupae and the maximum pupal size was achieved when five larvae were used for inoculation. Based on these results, we conclude that inoculating a single Z. atratus pupa with approximately five D. longulus first instar larvae is the most suitable propagation method.