Immature stages of development of the solitary endoparasitoid wasp, Trissolcus japonicus, on its host, Halyomorpha halys

Morphological changes of the immature solitary endoparasitic wasp, Trissolcus japonicus Ashmead (Hymenoptera: Scelionidae), were studied. A population of T. japonicus derived from Beijing, China is being tested as a potential biological control agent for the brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). This wasp attacks eggs of the BMSB, a serious invasive pest in the U.S. Due to the small size of T. japonicus, direct observation of its life stages is impossible in the field. We hypothesized that we could detect distinct life stages within the host and developmental differences between males and females. Six phases of preimaginal development were identified along with several other distinctive characteristics of parasitism. Developmental rates between males and females did not differ until eye sclerotization began on Day 14. Time to emergence and percent parasitism were also monitored. Males emerged on average four days faster than females at 20°C, 60% RH, and 16:8 L:D photoperiod. Percent parasitism in this study was 94%. In general, immature stages of endoparasitoids are poorly documented. This work contributes to a more thorough understanding of growth and maturation in this wasp. Knowing how to recognize the developmental phases will enable us to evaluate the success of T. japonicus as a classical biological control agent of BMSB if it is approved for release.