The observed population outbreaks and subsequent crashes correspond, essentially, to the aphid population switching rapidly from one locally stable manifold to another.
In general, the treatments with the largest concentrations of alfalfa also had the highest numbers of aphids.
This aphid migrates to other parts, including below-ground stems, and so space is less likely to be a limiting factor.
The model assumes that, initially, both aphids and natural enemies coexist at low densities (mathematically, at a stable equilibrium).
However, why the correlation was only significant at the higher aphid densities and not at the lower aphid densities remains unclear.
Such dramatic responses to aphid feeding are unusual and probably indicate the involvement of toxic aphid saliva or hypersensitive reactions of the cypress trees.
In this paper the hypothesis that the aphids' antennae are crucial for the wing induction in the presence of natural enemies is tested.
What is responsible for the apparent specificity of aphid resistance genes?
