Dynamics of Populations of Plant Parasitic Nematodes

Population dynamics have received a minimum of nematologists' and plant pathologists' attention from the time crop rotation was advised as a control measure against Heterodera schachtii in beets (2, 37) and H. ros­ tochiensis on potato (84). Al though population densities were not yet actually measured the advice was based on (i) the supposition that the damage to be expected is directly related to density of the nematode in the soil and (ii) the concept that mortality during a certain number of years in which no host is grown and therefore no food supplied balances population increase during a season in which a host is grown. If a is the rate of reproduction of the nema­ tode on a host, b the proportion of the population at the beginning of a year that survives through the year, and x the number of years in which no host plant must be grown to balance a, then ab ::; 1 or x ;::: log a/log b 1.