The spatio-temporal distribution of adult Ceutorhynchus assimilis in a crop of winter oilseed rape in relation to the distribution of their larvae and that of the parasitoid Trichomalus perfectus

The spatio-temporal distribution of Ceutorhynchus assimilis Payk. (Coleopte ra: Curculionidae) adults caught in a rectangular grid of flight traps in a crop of winter oilseed rape (Brassica napus L.) was mapped and was analyse d using Spatial Analysis by Distance IndicEs (SADIE). Their distribution wa s compared to that of their larvae and that of their parasitoid Trichomalus perfectus (Walker) (Hymenoptera: Pteromalidae) in pods. The distribution o f immigrating C. assimilis adults was consistent with their arrival at the crop boundaries and movement within the crop towards its centre. Adult C. a ssimilis were aggregated at all times, invasion being on two fronts, leadin g to the formation of two major clusters within the crop. Large areas of th e crop remained relatively unpopulated. During the emigration phase, number s declined simultaneously in all parts of the crop. The distributions of ad ult and larval C. assimilis and of larval T. perfectus were spatially assoc iated. The distribution of the parasitoid did not show a density dependent relationship with that of its host. We discuss the movements of insects whi ch underlie their population distributions, the value of integrating spatia l information into improved management strategies for C. assimilis and the potential for the spatial targeting of insecticides to reduce the amount ap plied and to conserve T. perfectus.