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SUMMARYThe ability of certain species of parasitic nematodes to survive desiccation for considerable periods is a fascinating example of adaptation to the demands of fluctuating environments that occasionally can become extreme and life threatening. Behavioural and morphological adaptations associated with desiccation survival serve primarily to reduce the rate of drying, either to prolong the time taken for the nematode's water content to reach lethal low levels or, in true anhydrobiotes, to enable the structural and biochemical changes required for long-term survival to take place. Examples of these adaptations are reviewed, together with information on the factors involved in rehydration that ensure successful exit from the dormant state. Information on desiccation survival is central to effective management and control options for parasitic nematodes. It is also required to assess the feasibility of enhancing the longevity of commercial formulations of entomopathogenic nematodes, both before and after application; current research and future prospects for enhancing survival of these bio-insecticides are discussed.

The total lipid content of the dry weight of whole cysts and 2nd-stage juveniles (J2) of Globodera rostochiensis was 17·1% in dry cysts, 20·9% in cysts soaked in distilled water (DW), 20·3% in cysts that had been in potato root diffusate (PRD) for 7 days, 7·3% in cysts that had been in PRD for 28 days and 29·2% for hatched J2. The fatty acid composition of the total lipid did not differ between dry cysts, cysts in DW and cysts in PRD for 7 days. However, major differences in the fatty acid composition of all lipid classes were found between rehydrated cysts in PRD and freshly hatched J2. After hatching, the degree of saturation and the percentage of monounsaturated fatty acids decreased and the percentage of polyunsaturated fatty acids increased considerably, especially in the free fatty acid fraction, where C20[ratio ]1 showed an 8-fold decrease and C20[ratio ]4 a 33-fold increase. There was a difference in the fatty acid composition of cysts in PRD for 7 days and cysts in PRD for 28 days (after most of the J2 had hatched); with increased time in PRD the percentage of polyunsaturated fatty acids increased and the percentage of monounsaturated fatty acids decreased in all lipid classes. Differences in the fatty acid profiles between cysts in PRD for 28 days and hatched J2 were found mainly in the free fatty acid and the non-acidic phospholipid fractions. The free fatty acid fraction of the cysts was dominated by monounsaturated fatty acids (52%), whereas the same fraction of hatched J2 contained large amounts of polyunsaturated fatty acids (60%). These polyunsaturated fatty acids, especially C20[ratio ]4, might play an important part in nematode–plant interactions during infection.

Electrophysiological techniques and behavioural assays were used to determine the response of males of Globodera rostochiensis to 4 fractions of the homospecific sex pheromone from virgin females, separated using reverse-phase high-pressure liquid chromatography. Sex pheromone activity was confined to 2 of the fractions. The sex pheromone of G. rostochiensis appears to be composed of several weakly basic, polar compounds.

SUMMARYIndirect immunofluorescent studies have been used to localize a glycoprotein (gp32) in the amphids of 2nd-stage juveniles (J2) of Meloidogyne incognita parasitic in the roots of tomato plants, male Meloidogyne javanica and some young adult female M. incognita. Immuno-electron microscopic studies showed an apparent absence of gp32 in the amphids of mature adult female M. incognita. Chemoattraction experiments demonstrated that the binding of gp32 antibodies to the amphidial secretions of infective J2 M. incognita partly impaired the ability of the nematodes to locate tomato roots.

Electrophysiological techniques were used to obtain recordings of extracellular electrical activity from the anterior end of live adult females of Brugia pahangi. Stimulation with 100 mM, 10 mM and 1 mM acetylcholine resulted in an increase in spike activity which was concentration dependent, whereas stimulation with phosphate-buffered saline and 0.1 mM acetylcholine gave no increase in activity. The delay in response was not concentration dependent. The action of possible host cues was investigated. Stimulation with heat-inactivated foetal calf serum (IFCS) and 10 mM glutathione gave an increase in spike activity but exposure to 5 mg/dl haemoglobin elicited no response. The response to IFCS was found to be suppressed completely by pre-incubation for 30 min in ivermectin.

Nematology is divided, often arbitrarily, into several ‘subdisciplines’, amongst which the study of plant-parasitic nematodes is predicated on their considerable economic importance world-wide. Further subdivision of the discipline is rarely justified but, in the tropics and subtropics, control of nematode damage is often compromised by lack of knowledge and the cost of conventional management strategies. Thus, there is a need for a comprehensive, informative text on plant-parasitic nematodes of these regions. Plant Parasitic Nematodes in Subtropical and Tropical Agriculture is the second edition of a book whose aim is to meet these requirements.

Investigations of nematode hatching have concentrated on the parasitic forms, especially on synchronization between host and parasite life-cycles which, in some species, is so close that the parasite is dependent on the host for the hatching stimulus. Research into nematode hatching reflects the artificial separations created throughout nematology by defining research groups and their activities in terms of the host; consequently, useful comparisons between hatching of plant and animal parasitic nematodes have been few. With the increasing use by geneticists of nematodes as model animals and the interest in them by neuro-physiologists, molecular biologists and others, we hope that such distinctions will be lessened.

The cuticular permeability of anhydrobiotic 4th-stage juveniles of Ditylenchus dipsaci decreases during rehydration, as indicated by staining with osmium tetroxide, the measurement of permeability coefficients by the rate of uptake of tritiated water from a HOH/C-inulin bathing solution and by an increased ability to slow down the rate of water loss and to survive subsequent desiccation. The initial decrease in permeability coefficient is rapid, suggesting a physical effect due to the rehydration of the cuticle, followed by a slower reduction over the subsequent 1–4 h which is dependent upon metabolic activity. The reestablishment of the permeability barrier is sensitive to metabolic inhibitors which affect enzyme activity and post-transcriptional protein synthesis. Sodium iodoacetamide was the only inhibitor which affected maintenance of the permeability barrier. An Arrhenius plot of changes in cuticular permeability with temperature indicated a sharp increase in permeability at 40–50°C and brief exposure to diethyl ether resulted in loss of the permeability barrier, suggesting that a superficial layer, probably the epicuticle, is responsible for controlling cuticular permeability.

SummaryWhen eggs ofAscaris suumwere transferred from glass-distilled water into 0·1–0·4mNaCl solutions, the water content of the unhatched juveniles fell with increasing concentration of solute. The effect was reversible. The egg-shell was thus permeable to water. The osmotic pressure of the egg fluid was osmotically equivalent to between 0·1 and 0·2mtrehalose. In hatching experiments in Fairbairn's medium containing 0·1 or 0·2mtrehalose, only 5 and 3% respectively of the eggs hatched; 83% of the eggs hatched in the absence of trehalose. The evidence suggests that loss of solutes from the egg fluid permits an increase in the water content of the unhatched juveniles and that this may be responsible for ending their quiescence.