Colonisation of tomato fields by predatory mirid bugs (Hemiptera: Heteroptera) in northern Spain

Dicyphus tamaninii and Macrolophus caliginosus are predatory bugs that significantly contribute to control of pests in tomato crops following early colonisation in spring from winter refuges. This paper aimed to determine the influence of the richness of nearby potential predator sources at the time of arrival, amount and establishment of the mirid bugs in tomato fields. For this, six tomato fields were selected that showed a gradient of vegetational settings in the landscape. Crops and non-crop vegetation were sampled with a vacuum suction sampler and abundance of potential colonising predators was estimated. Soon after transplantation of tomatoes, weekly visual counts on the crop were initiated and continued for 8 weeks to estimate densities of Trialeurodes vaporariorum adults, the most abundant pest, and predator adults and nymphs. Time of predator arrival in each field, which varied between 6 and 8 weeks after seedling transplantation, was not related to the respective predator abundance in the surrounding vegetation. Eleven weeks after transplantation, fields differed in their cumulative numbers of insect-days (greenhouse whitefly, predator adults and nymphs). Differences in predator-days were not related to densities of greenhouse whitefly-days but to predator abundance in field surroundings. Fields were also colonised by predators coming from distant sources. Mirid bugs were more abundant in outer rows, particularly in fields with close predator sources and were concentrated on plants with higher whitefly densities. Predator nymphs were detected soon after adult arrival and distributed in the field mostly according to adult predator or prey spatial pattern. Presence of winter refuges for predators in nearby habitats increases the amount of colonisation. However. in order to rely on predator colonisation into fields, the stimuli involved in the predator movement from winter refuges to crops and the predator dispersal capacity should be further investigated. (C) 2002 Elsevier Science B.V. All rights reserved.