The effect of previous desiccation on the ability of 4th-stage larvae ofDitylenchus dipsacito control rate of water loss and to survive drying

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Abstract
The desiccation survival of 4th-stage larvae of Ditylenchus dipsaci revived from dry worm aggregations (‘wool’ larvae) was compared with that of larvae extracted from narcissus bulbs (‘bulb’ larvae). Both sorts survived desiccation well, but ‘wool’ larvae survived desiccation at various humidities somewhat better than ‘bulb’ larvae. The rate of drying of the former was more rapid than that of the latter; the ability to control water loss, therefore, does not of itself ensure survival. The number of larvae reviving decreased with repeated cycles of desiccation and hydration, and also with the increase in the period during which the nematodes were kept dry. However, this was not associated with any loss of ability to control drying. The rate of drying of ‘wool’ larvae remained unaltered irrespective of previous desiccation treatment. In contrast, the rate of drying of ‘bulb’ larvae was more rapid after an initial desiccation with the result that ‘bulb’ larvae dried at the same rate as ‘wool’ larvae. While ‘wool’ and ‘bull’ larvae differed initially in both the rate of water loss and survival, a period of desiccation eliminated only the difference in water loss.The results suggest that the rate of drying is dependent largely on physical factors. It was shown, however, that the cuticle of dead larvae was completely permeable to water in both directions. Therefore the ability to control water loss must, in some as yet unknown way, be connected with the nematode as a living system.