Abstract
The cabbage root fly, Delia radicum, at Silwood Park is attacked by both generalist and specialist natural enemies. This paper uses spatial and temporal census data to examine the relative contributions of these natural enemies to the population dynamics of D. radicum. Data on the distributions and mortalities of D. radicum on 40 swede plants in nine consecutive years have been analysed. Using a maximum likelihood technique, the parameters (together with their support limits) have been estimated from these data for a model of an insect host - generalist - specialist interaction. Three particular cases of the model are analysed: (i) only the generalist, Aleochara bilineata, is present; (ii) only the specialist, Trybliographa rapae, is present; and (iii) both species of natural enemy are present
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