Modelling populations of cyst-nematodes (Nematoda: Heteroderidae)

SUMMARY
(1) Because cyst-nematode populations are relatively static, immigration and emigration
are negligible and population fluctuations under different crops can be studied in small field
plots. A modification of the logistic equation (see eqn (10)) for population growth adequately
describes the relationship between initial and final population densities during one growing
season on a susceptible host crop. This equation allows for eggs that persist unhatched and
for damage to the host root system. Population oscillations are considered both theoretically
and in relation to field data.
(2) Equations are proposed for the effects on populations of non-host and resistant crops,
fumigant or oxime carbonate nematicides, selection of pathotypes within species, competi-
tion between sibling species, and the effects of ground-keepers (weed hosts).
(3) A computer program has been developed which simplifies the fitting of the population
equations to field data and enables the effects of crop rotations on population densities to be
simulated. Some samples of computer output are given illustrating the predicted effects of
rotations on population density and population genetics. The equations developed for
Globodera spp. also apply to related Heterodera spp., especially those with one main
generation a year.
(4) The difficulties of fitting the model to field data, the limitations of modelling, unsolved
problems in extending the models to species with more than one generation and the need to
take account of variable environmental factors are discussed.
RESP-7809