Modelling populations of cyst-nematodes (Nematoda:Heteroderidae).
Abstract
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 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. Equations are proposed for describing the effects on the nematode populations of non-host and resistant crops, fumigant or oxime carbonate nematicides, the selection of pathotypes within species, competition between sibling species, and the effects of ground-keepers (weed hosts). A computer program has been developed which simplifies the fitting of the nematode 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. 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.