ON SIZE AND MOLTING OF APHELENCHUS-AVENAE (NEMATODA, APHELENCHIDA)

The classical hypothesis of nematode growth, that stretch receptors initiate a moult to remove the limitation to growth imposed by a tightly stretched cuticle, could not be substantiated in the free-living, fungal-feeding nematode, A. avenae. No evidence that the cuticle limited growth in either juveniles or adults was obtained. A moulting cycle was initiated after a minimum period of feeding; length at the following moult was related to duration of feeding within a stage. Differences in length of juveniles at the second or third moults had no effect on the length in the fourth stage at which the moulting cycle was initiated. Evidence suggested the stimulus for moulting was an adequate supply of a chemical(s), which could be ingested or metabolized in the immediate stage or the previous stage so that increase in length was not directly related to moulting. Length at the fourth moult had no effect on maximum length of adults. Minimum length of adults was that at which the stimulus for moulting was received in the fourth stage; maximum length was about three times minimum length. A hypothesis for growth and development of nematodes is proposed. © 1990.