The rate of development of sterile 2nd-instar beet eelworm (Heterodera schachtii Schm.) larvae to the adult stage on excised sterile roots of sugar beet (Beta vulgaris L.) was studied.

Culture methods were as previously described (Moriarty, 1964). Sterile excised sugar-beet roots were placed on White's medium gelled with 0·75 % agar, inoculated with about 0·1 ml of an aqueous suspension containing several hundred sterile 2nd-instar eelworm larvae, and kept at 25 ± 0·5 °C. After 24 h the roots were transferred to liquid White's medium. Two roots were stained in acid fuchsin lactophenol (Goodey, 1963) every 24 h, for 19 days. Later, the length of main root axis and total length of laterals were measured, the number of laterals counted, the eelworms dissected out and the larval instars identified (Raski, 1950).

When roots were removed for staining, the liquid medium was examined for eelworms. Only adult males were ever found, and these are included in the counts in Table 1.

The rate of development of larvae varied greatly, about half did not develop beyond the 2nd instar (Table 1) and from the fifth day onwards some atrophied. One root in which many adults developed was kept 41 days before killing and staining: there were still some 2nd-instar larval cuticles, devoid of contents except for the buccal stylet, and presumably dead. The average number of all instars found per root did not decline during the 19 days of observations: therefore few of the atrophying larvae could have been missed. The percentage of larvae that entered the roots was variable and small.