Abstract
The causes of the erratic seasonal variation in the sizes of some insect pest populations are largely unknown, but they are believed to be associated, at least in part, with environmental change. The attendant lack of predictability makes the control of insect pests difficult, resulting in substantial losses. In a model simulation study, using parameter values based on field data, it is shown that under certain conditions a population experiencing regular periodic cycles (therefore being predictable) can become chaotic (i.e. erratic) in the absence of changes in environmental factors. Moreover, after a time the population returns to regular stable cycles. The process recurs and represents an intrinsic characteristic of the system. This phenomenon, known as intermittency, occurs when certain variables have values that place the system near the transition point between order and chaos. This discovery may help explain the erratic behaviour of some insect pest population and aid in developing better biological control measures.
