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The use of colloidal silica as a medium for the extraction of nematodes by flotation was examined in order to rationalise the diverse range of methods currently in use. Significantly more nematodes were extracted from small samples of rhizosphere soil and estuarine sediment by using colloidal silica (Ludox HS30 diluted to 1.10 g cm -3 with water) than by density-gradient centrifugal flotation in sucrose, a modified Baermann funnel extraction or by repeated decantation. No benefit was gained by using polyvinylpyrrolidone coated silica (Percoll), by initial mixing of the sample with kaolin or by using density-gradient centrifugation rather than centrifugation of a sample/Ludox mixture. Increasing the amount of sample mixed with a given amount of Ludox gave a linear increase in nematodes recovered up to a critical point (0.036 g rhizosphere sample and 0.221 g estuarine sample ml -1 Ludox). Rhizosphere nematodes passed through a 53 μm mesh and the sample/Ludox mixture required centrifugation so that the sample could be filtered through a 15 μm mesh. Estuarine nematodes were retained by a 53 μm mesh and simple sedimentation of the sample/Ludox mixture was sufficient for extraction.

Xiphinema diversicaudatum induced similar morphological changes in root-tips of strawberry, a good host, and ryegrass, a poorer host. After nematodes had fed for 1, 2, and 4 days the feeding site became surrounded by multinucleate hypertrophied cells with amoeboid-shaped nuclei, enlarged nucleoli and dense cytoplasm. Cell complexes also developed in association with the stelar initials in strawberry but not in rycgrass. There was an increase in the proportion of cytoplasm, from 47% to 56% of the root-tip volume, and a reduction in the proportion of vacuole from 40% to 28% after 1 day in strawberry. There was no change in the proportion of these components in ryegrass after nematodes had fed for 1 day. The total volume of the root-tip increased more in strawberry (8.5 x ) than in ryegrass (3.6 x ), but the concentrations of RNA and protein progressively decreased. Total RNA and protein both increased 3.4 x after 4 days in strawberry, but in ryegrass protein increased 2.7 x and RNA 5.4 x after 4 days. These results support an earlier hypothesis that strawberry nuclei are more transcriptionally active than ryegrass nuclei, and suggest that the metabolism of the two host plants had responded differently to feeding by X. diversicaudatum.

Reproduction by Xiphinema diversicaudatum on strawberry (good host) and raspberry (poor host) and by Longidorus elongatus on strawberry (good host) and turnip (poor host) was examined in a glasshouse pot trial at 18°C. Populations of X. diversicaudatum increased 32-fold on the good host and those of L. elongatus 34-fold, while on the poor host populations of both nematodes increased 8-fold. The observed generation times for X. diversicaudatum were 23 weeks on strawberry and greater than 23 weeks on raspberry, and for L. elongatus were 17 weeks on strawberry and 21 weeks on turnip. The generation times were extrapolated into field conditions. There were more females with eggs, and more eggs per female on the good host than on the poor host. The total volume of nematode supported by a host plant only increased appreciably when L3, L4 or adults were present in the sample, and the good host supported 5 times the volume of X. diversicaudatum and 8 times the volume of L. elongatus than did the poor host. More galls were formed on the root system of the good host, by X. diversicaudatum and by L. elongatus, than on the poor host. The ratio of galls/nematode was such that on strawberry X. diversicaudatum induced more galls, a maximum of 0.31 galls/nematode, than L. elongatus, a maximum of 0.14 galls/nematode.

Longidorus elongatus and L. leptocephalus fed only at the root-tip of perennial ryegrass growing in agar. Galls were usually fed upon by several nematodes. Feeding behaviour was similar for L. elongatus and L. leptocephalus; the root-tip was penetrated by rapid thrusts with the stylet to several cells deep within the root, following which there was a period of inactivity when the nematodes were thought to be salivating. Ingestion followed and continued for long periods without pause, with the odontostyle-tip in the same cell. During most feeds there were two or three periods of ingestion, separated by short (c. 2 min) periods of inactivity. Calculations based on measurements of the oesophageal bulb chamber, assuming 10% pumping efficiency, indicate that a volume equivalent to more than 40 cells may be extracted by a single nematode feeding for 1 h. Ultrastructural studies of galls formed during 8 days by L. elongatus showed that there were many empty cells in which the walls were holed. It is suggested that these holes result from action of the nematode saliva and that their formation eased removal of the contents of cells distant from the odontostyle-tip.