On hormonal control of moulting in Aphelenchus avenae (Nematoda: Aphelenchida).

Ligatures applied to juveniles of A. avenae at particular developmental times and positions limited the moult to the anterior or posterior portion of the nematode. To partition the moult, ligatures needed to be applied from about 4 h after receipt of the stimulus for moulting up till the onset of lethargus. Nematodes which were ligated before the stimulus failed to moult, while nematodes which were ligated after the onset of lethargus moulted on both sides of the ligature. If, at the appropriate time, ligatures were placed in the anterior third of the nematode, then the posterior portion of the nematode moulted; if the ligatures were placed in the posterior half, then the anterior portion of the nematode moulted. If the ligatures were placed between third and half the length of the nematode, then either the anterior or posterior portion moulted, or moulting was prevented. Extracts of lyophilised samples of mixed populations of A. avenae induced about 20% pupation in Musca domestica bioassays giving a weight of 80-320 ng ecdysteroid/g dry weight of nematodes. Externally applied 20-OH ecdysone at 2 x 10(-3) M stimulated moulting in the non-moulted portion of ligated nematodes but 2 x 10(-7) M did not.