Desiccation survival of larval and abult stages of the plant parasitic nematodes,Ditylenchus dipsaciandD. myceliophagus

Abstract

The effect of different relative humidities on the survival of individual larvae and adults ofDitylenchus dispasciand D.myceliophagushas been examined; experiments were carried out at 5 and 18°C with D.myceliophagusand at 18°C with D.dipsaci. Survival of both species was enhanced when they were dried at high humidities and, for D.myceliophagus, by the lower temperature. The survival of all stages of D.myceliophaguswas poor. Generally it was expressed in minutes only; 4th-and 3rd-stage larvae, however, were marginally better at surviving drying than adults and much better than 2nd-stage larvae.Although the 4th-stage larva of D.dipsaciwas overwhelmingly superior to all other stages, the 3rd stage, and to a lesser extent, the adult of this species also showed remarkable powers of survival to desiccation. In general, survival of 4th-, 3rd- and 2nd-stage larvae could be expressed in weeks, days and minutes respectively; for adults, survival was expressed in hours at relative humidites under 50% but in days at higher relative humidites.The results are discussed in relation to the survival value of the aggregations formed by these species; the validity of the term ‘resistantstage’ as applied to the 4th-stage larva of D.dipsaciis assessed.