The Capsule and Its Relation to the Embryogenesis of the Ichneumonid Parasitoid Mesoleius Tenthredinis Morl. In the Larch Sawfly, Pristiphora Erichsonii (Htg.) (Hymenoptera:tenthredinidae)

Eggs of the parasitoid Mesoleius tenthredinis Morl. from British Columbia develop and hatch in approximately 120 hours when reared at 23 ± 0.5 °C and a relative humidity of 72 ± 2% within field-collected larch sawfly (Pristiphora erichsonii (Htg.)) larvae from British Columbia and Newfoundland, and within laboratory-reared P. crichsonii larvae from British Columbia. However, they develop normally for only 70 to 80 hours within field-collected larvae from Manitoba as encapsulation of the developing eggs occurs and development ceases in the late germ band stage. The capsule is formed by an accumulation of host blood cells. During the formation of the capsule the innermost blood cells become flattened, fibrous, and enucleated, and eventually form a mass of concentric sheaths of non-cellular material. Thus, the definitive capsule is both cellular (outer region) and non-cellular (inner region). Histochemical tests indicate the presence of mucopolysaccharide in the capsule. It is suggested that the capsule inhibits the embryonic development of the parasitoid by interfering with its oxygen supply.