The effect of the area and configuration of hibernation sites on the control of aphids by Coccinella septempunctata (Coleoptera:Coccinellidae) in agricultural landscapes:: A simulation study

The lady beetle Coccinella septempunctata L. is an important predator of aphids in arable crops, but depends on noncrop landscape elements, such as hedgerows, for hibernation. We studied the effect of the shape, area, and fragmentation of noncrop landscape elements on the control of aphids by C. septempunctata using a spatially explicit simulation model. The model is based on a description of the phenology and population dynamics of aphids and C. septempunctata, as well as the predation dynamics and dispersal characteristics of C. septempunctata. The study compares biocontrol in 12 landscapes consisting of field crops and hedgerows that differ in the shape, proportion (1, 4, 9, and 16%), and fragmentation of the hedgerow elements (hedgerow area divided into 1, 4, or 16 elements) in the landscape. Linear hedgerow elements provided better control than square elements in 3 of the 12 simulated landscapes and resulted in similar levels of control in the other nine landscapes. The total area of hedgerow habitat was the key factor for the control of aphid populations. Landscapes with 9% and 16% noncrop habitat had large enough local populations of C. septempunctata to control aphid infestations, whereas landscapes with only 1% or 4% of hibernation area had no potential for improved aphid control. In landscapes with sufficient noncrop habitat, the best control was achieved when small hedgerow elements were evenly distributed over the landscape.