The 'Natural Enemy Ravine' in cereal aphid population dynamics: a consquence of predator activity or aphid biology?

Abstract

1. Although `natural enemy ravines' (Southwood & Comins 1976) may exist, similar ravines in population growth rate surfaces can result from processes other than predation.
2. The discontinuous colonization of cereal crops by alate aphids and the time it takes for their nymphs to reach maturity also cause the `ravines' in the population growth trends of cereal aphids.
3. This is supported by detailed field studies and by the trends in population growth predicted by a simulation model in which the pattern of crop colonization was varied.