Fluctuations in the Distribution and Numbers of Helicotylenchus Dihystera in Kikuyu Turf (Pennisetum Clandestinum)

Studies of fluctuations in numbers of Helicotylenchus dihystera in an area of kikuyu turf (32 X 16 m) from March 1974 to May 1975 indicated that: (1) populations within the area fluctuated asynchronously in time (2) such fluctuations were superimposed on a general seasonal trend (3) there were some centres of permanently high and low populations. Attempts to correlate nematode numbers with environmental components were unsuccessful. Further measurements suggested that as the size of an area increased so the reliability of the estimate of mean density decreased. To obtain a reliable assessment of the mean density of a nematode species in a large area is very time consuming and may have little meaning if there is considerable environmental variability within the area. It is suggested that large areas should first be mapped to indicate this environmental variability thus enabling stratified sampling to be used.