Interference microscopy has been used to study the rate at which water enters and is lost from larval and adult stages of Ditylenchus dipsaci and D. myceliophagus. It is shown that the cuticle of the dry nematode, irrespective of stage, is completely permeable to water. In contrast, marked intra– and interspecific differences were found in the rate at which stages dry at 0 and 50% relative humidity. All stages of D. myceliophagus dry very rapidly: in this species, death, as a consequence of severe desiccation, appears to be linked to a lack of any marked ability to control water loss. For D. dipsaci, those stages known to survive desiccation will appear to be the slower dryers. In general, the “order of performance” in slowing the rate of drying is the same as the order previously found for survival of desiccation. Both the 4th– and, to a lesser extent, the 3rd–stage larvae of D. dipsaci show evidence of an intrinsic ability to control water loss.
An analysis of the drying curve for 4th–stage larvae of D. dipsaci supports the indications of interference photographs that the rate of drying is slowed by a decrease in permeability of the drying cuticle.
Vacuum desiccation studies further demonstrate the remarkable ability of the 4th–stage larva of D. dipsaci to control its rate of drying. The survival of 4th– and 3rd–stage larvae of D. dipsaci is diminished by very rapid drying, and the survival of other stages of this species and larval and adult stages of D. myceliophagus is precluded. The decrease in survival of the 4th–stage larvae of D. dipsaci is shown to be associated with a more rapid rate of water loss.