A population model for the effect of parasitic fungi on numbers of the cereal cyst-nematode, Heterodera avenae.
Population densities of Heterodera avenae in a sandy soil in Nottinghamshire, UK, decreased to very low levels between 1957 and 1968, despite intensive cropping the cereals [Hm/B 39: 17]. Similar unexpectedly small populations have been recorded after intensive cereal cultivation at other places [Hm/B 47: 519]. Such decreases were attributed to a fungal parasite which attacks young females, and the nematode, which reached pest proportions some years ago, is now strongly controlled in most fields. A population model is described for this effect, and theoretical considerations show that it predicts the attainment of low stable equilibrium densities. A simplified version gives a good fit to the field data.