EMBRYONIC-DEVELOPMENT OF AN ENDOPARASITOID, MICROPLITIS-CROCEIPES (HYMENOPTERA, BRACONIDAE) IN CELL LINE-CONDITIONED MEDIA

Embryos of the parasitoid Microplitis croceipes develop from pregerm b and stage to first larval instar in cell culture medium conditioned by a cell line (IPLB-LdFB) derived from fat body from an atypical host L ymantria dispar. However, the percentage of eggs that develop normally to the first larval instar stage is significantly less than for those maintained in IPL-52B medium conditioned with host fat body tissue. T herefore, we examined the capacity of five insect cell lines to promot e growth and development of pregerm band eggs in five media, IPL-52B, TC-199, TC-100, Grace's, and ExCell 400. The developmental response of M. croceipes was dependent both on the cell line and the cell culture medium used. TC-100, TC-199, and Grace's media promoted development t o the germ band stage without the need for conditioning with host tiss ue. IPL-52B supported development to the germ band stage when a define d lipid concentrate was added. In IPL-52B medium, the IPLB-LdFB cell l ine promoted a significantly higher number of eggs developing to germ band relative to the other cell lines; however, none of the cell line- conditioned IPL-52B medium significantly stimulated egg hatch relative to the control medium. None of the cell line-conditioned Grace's medi a had a significant effect on eggs attaining germ band stage compared with the Grace's control medium. However, Grace's medium conditioned w ith the IAL-TND1 and IPLB-LdFB cell lines promoted development beyond germ band, resulting in a significantly higher percentage of hatching eggs than the Grace's control medium. Although the BCIRL-HZ-AM1 cell l ine, which is derived from the parasitoid's typical host, did not indu ce hatch in either IPL-52B medium or Grace's medium, it promoted hatch in TC-199 and Excell 400 media. Fat body taken from the same species that the cell lines were derived from was a better predictor of a cell line's embryotrophic activity in Grace's medium rather than in IPL-52 B medium. Thus, the composition of the medium and the species and tiss ue type of the cell line source must be evaluated interactively to det ermine optimal conditions for promoting development of M. croceipes in vitro.