Spatio-temporal distributions of Meligethes aeneus and its parasitoids in an oilseed rape crop and their significance for crop protection

The distributions and phenology of Meligethes aeneus and its parasitoids were studied in relation to the potential value of spatio-temporal information for integrated crop management (ICM) and the conservation management of parasitoids. Insects were sampled at 40 spatially-referenced points within a crop of winter oilseed rape and the following winter wheat crop. Spatial distributions were analysed and compared using Spatial Analysis by Distance IndicEs (SADIE). A quarter of M. aeneus larvae were parasitised by Phradis interstitialis and Tersilochus heterocerus but fewer than two percent of parasitised hosts gave rise to parasitoid adults. Adult P. interstitialis emerged from overwintering two weeks before T. heterocerus which was the more abundant. Both adult and larval M. aeneus distributions showed clustering in the north-eastern half of the field. The distribution of P. interstitialis larvae was associated with that of their host whereas the eggs of T. heterocerus were spread evenly across the field. Opportunities for conservation of parasitoids by spatio-temporal targeting of insecticides are discussed.