CHRONOLOGY AND STUDY OF THE PSEUDOCYSTS O F HELIGMOSOMOIDES-POLYGYRUS-POLYGYRUS (DUJARDIN, 1845) (TRICHOSTRONGYLINA-HELIGMOSOMOIDEA), A PARASITE OF APODEMUS-FLAVICOLLIS IN FRANCE - COMPARISON WITH THE RELATED SPECIES

The biology of the three species of Heligmosomidae, common among roden ts in France, was studied in their respective natural hosts. Microlus arvalis for Heligmosomoides laevis, Apodemus flavicollis For Heligmoso moides polygyrus polygyrus and Clethrionomys glareolus for Heligmosomu m mixtum. The morphogenesis had been studied in a first paper (N'Zobad ilo et al., 1996). This second paper deals with the chronology of the moults, the migrations iii the vertebrate host and the formation of ps eudocyst; in the three species, a number of larvae develop in a pseudo cyst while the others do not leave the intestinal lumen, but, in both cases, the time required For the development remains similar. The Heli gmosomidae have similar biological characteristics but which ore more developed than those of the rodent parasites Nippostrongylinae (Heligm onellidae). However, there are some slight biological differences betw een them, in regard to their degree of morphological specialization. T hus the more primitive the species is, the more frequent the formation of pseudocysts. The pseudocysts of the Heligmosomidae ore interpreted as phenomena representing the genetic baggage of evolution whereas th e Nippostrongylinae penetrate through the skin and migration through t he lungs is necessary to reach the intestine, the Heligmosomidae, more evolved, penetrate orally and migration through the lungs becomes unn ecessary. The facultative maturation of the larvae in a pseudocyst the refore may fulfil the necessity of the larva for somatic migration. Am ongst the Trichostrongylidae of ruminants, the same phenomenon can res ult in a larval diapause, which could represent on adaptation process contributing to the survival of the worms when the environmental condi tions, particularly climatic ones, are unfavourable.