Nesidiocoris tenuis(Reuter) (Hem. Miridae) is a native zoophytophagous predator of the Mediterranean region, and its populations colonize tomato crops when they are not heavily treated with insecticides. This generalist predator has a high capacity for controlling insect pests, and it is currently commercially produced and released in some areas to controlBemisia tabaci(Gennadius) (Hem. Aleyrodidae). However, its status as a pest and/or as beneficial is controversial. Therefore, the aim of this study was to evaluate the risk of damage to tomatoes in extreme conditions of prey scarcity, as well as high predator populations. Three predator densities were tested in a greenhouse cage experiment during a summer tomato crop. The crop did not display any negative effect caused by the predators during the first six weeks of interaction, independently of the density released. However, subsequently, the effect was dramatic, both on the vegetative growth of the plant and on the production of fruits. The reduction in vegetative growth was located at truss eight and it was expressed mainly by a lower number of leaves and a shorter length of the shoot above the truss. There was a significant reduction of yield with a lower number of fruits collected and a smaller mean weight, although this was not observable until truss seven. It seems that feeding on the plant by this mirid bug competed with the vegetative growth and fruiting processes of the plant in the extreme conditions of prey shortage maintained in our experiment.

Predatory insects of Frankliniella occidentalis (Pergande) were surveyed from the summer of 1991 through the autumn of 1992 in nonsprayed vegetable and ornamental crops on the north Mediterranean coast of Spain. The predatory fauna comprised insects in 5 orders, 8 families, and 18 species. The anthocorid bugs Orius laevigatus (Fiever) and O. majusculus (Reuter) and the mirid bugs Dicyphus tamaninii Wagner and Macrolophus caliginosus Wagner were the most numerous and widely distributed species observed, constituting 95% of all predators. All 4 of these species were able to complete their nymphal development feeding on F. occidentalis nymphs. Developmental periods of both mirid bugs species was longer than that of both anthocorid bug species. Prey consumption during nymphal stages was high and similar for all 4 predator species. Adults of all 4 species consumed a higher number of F. occidentalis nymphs than did their nymphs. Fecundity and longevity were higher for both anthocorid bug species compared with both mirid bug species. The potential of all 4 species for biological control of F. occidentalis is discussed.