[Histological observations of the capsules induced by Contortylenchus diplogaster v. Lins (Nematoda: Allantonematidae) in the adipose tissue of Ips sexdentatus Boern. (Coleoptera: Scolytidae)].

The evolution of the capsules induced by C. diplogaster in the fat body of I. sexdentatus is followed by histological methods from the pupal stage to the oviposition of the host. Early in the pupal stage of the insect, the parasitic female of C. diplogaster has not oviposited yet and the nuclei of the capsule that surrounds it are gathered in tetrads; some of these nuclei are in a well forwarded degenerescence. These observations suggest that the syncytial capsule should result both from an amitotic division of the nuclei followed by a degenerescence of some of them and from a fusion of cells. Late in the pupal stage, the nuclei are set apart from each other and distributed at the periphery of the capsule. The oviposition of the nematode takes place when the host is an adult. After the development of the larvae has been made into the capsule, this one ends in breaking, generally when the bark beetle has attacked a new host-tree. Then, the larvae of the nematode leave the insect and invade the galleries. The parasitic development of C. diplogaster always takes place quite in the fat body of the beetle.