THE LENGTH OF STRONGYLID NEMATODE INFECTIVE LARVAE AS A REFLECTION OFDEVELOPMENTAL CONDITIONS IN FECES AND CONSEQUENCES ON THEIR VIABILITY

Isolates from eight gastro-intestinal nematode species of sheep, cattl e and deer parasites were maintained in sheep and faecal cultures were processed at different temperatures (for four species) and moistures (for the eight species). For all the tested species, the third-stage l arvae (L3) were longer at temperatures optimal for development and the ir length increased linearly with faecal moisture contents (FMC). Thes e variations in length mainly concerned the volume of intestinal cells . The length of L3 had no consequence on their survival in water at ro om temperature (five species tested), but the short L3 migrated more s lowly on agar gel than did the longer ones (verified for three species ) and exsheathed more slowly (verified for two species). The establish ment rate observed for short L3 of Teladorsagia circumcincta in lambs was lower than that seen for long L3 in three other lambs, but the dev eloped worms were similar in length and fecundity. These results are r elevant to our understanding of how the different species could adapt to and/or compensate for adverse conditions of development.