Movement of greenhouse whitefly and its predators between in- and outside of Mediterranean greenhouses

Some Mediterranean greenhouses are inserted in a landscape of open fields, non-agricultural and woody habitats. Both the greenhouse whitefly and its polyphagous predators are well adapted to protected and field crops. The phenology and intensity of whitefly and predator exchange between greenhouses and surrounding habitats were investigated in two different zones of northern Spain. Whiteflies colonised greenhouses earlier and built up high populations before predators established in the crop. Both the abundance of vegetation and the topographic characteristics of the environment surrounding greenhouses affected the numbers of predators entering the tomato crop through the greenhouse openings whereas whitefly migration was only affected by the topography around the greenhouses. These results are discussed in terms of biological control of greenhouse pests by naturally occurring predators. (C) 2003 Elsevier B.V. All rights reserved.