Risk of damage to tomato crops by the generalist zoophytophagous predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) J. Arno ´, C. Castan ˜e ´ * , J. Riudavets and R. Gabarra IRTA, Carretera de Cabrils Km 2, 08348-Cabrils (Barcelona), Spain Abstract 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 control Bemisia 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. Keywords: omnivore, crop damage, biological control, population dynamics, whitefly (Accepted 4 February 2009) Introduction Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is a cosmopolitan species whose status as a pest and/or as ben- eficial has been controversial for a long time. While con- sidered a pest of tobacco by Indian researchers (Prasad et al., 1979; Patel, 1980), it was considered as beneficial to tobacco in the Philippines due to its high predation efficiency on Spodoptera litura (F.) and the lack of damage to the crop (Torreno, 1994; Torreno & Magallona, 1994). In the Medi- terranean region, it was first mentioned as a pest for tomatoes by El-Dessouki et al. (1976) in Egypt, who de- scribed the damage produced on stems and shoots by the repeated feeding punctures of the stylet in these tissues. Although in Sicily it was initially described as a pest due to the brown rings produced on tomato shoots, as well as flower abortion, its role as an efficient predator was also considered and discussed (Vacante & Tropea-Garcia, 1994). In the south of France, it has always been considered as a pest of tomatoes (Trottin-Caudal & Millot, 1997; Trottin- Caudal et al., 2006); but, in the Canary Islands (Carnero et al., * Author for correspondence Fax: +34 937 533 954 E-mail: cristina.castane@irta.es Bulletin of Entomological Research (2010) 100, 105–115 doi:10.1017/S0007485309006841 Ó Cambridge University Press 2009 First published online 14 April 2009