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The survival capacities of Muellerius capillaris (Nematoda: Protostrongylidae) free-living larval stages (L1) of an Israeli desert isolate (Nubian isolate) (92 mm rain per annum) and a French isolate from a temperate habitat (650 mm rain per annum) were compared under humid and extreme dry conditions. Under the dry conditions (7% relative humidity [r.h.] and 33% r.h. at 23 degrees C), both isolates exhibited the same remarkable survival capacity for periods of 17 and 28 days, respectively (>92%, survival, P > 0.1). However, during and after recovery from the anhydrobiotic slate, different behaviour patterns of L1 were observed in each isolate. Under humid conditions (97%, r.h.) for 10 days, both isolates exhibited similarly low survival percentages (13.4 +/- 4.6%, S.E., survival for the Nubian isolate, 3 +/- 3 0,6 for the French isolate, P > 0.05). In water, the French isolate was less active, survived better (52 +/- 8.4%, vs 28.7 +/- 3.7, by day 28, P < 0.05) and retained a better morphological appearance (shrunk less) than the Nubian isolate. Larval development of the French isolate in the land snail Theba pisana was significantly faster than that of the Nubian isolate, reaching a higher proportion of infective stages (L3) on day 36 post-infection (78.6% vs 56% P > 0.05). However, similar infection intensities were recovered in snails infected with either of the isolates (59.8 +/- 10.3, S.E., n = 14, for the French isolate, 53 +/- 6, n = 13, for the Nubian isolate, P < 0.05).