INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY ISSN Print: 1560–8530; ISSN Online: 1814–9596 07–344/SAE/2008/10–5–521–525 http://www.fspublishers.org Full Length Article To cite this paper: Fathi, S.A.A., A. Asghari and M. Sedghi, 2008. Interaction of Aeolothrips intermedius and Orius niger in controlling Thrips tabaci on potato. Int. J. Agri. Biol., 10: 521-5 Interaction of Aeolothrips intermedius and Orius niger in Controlling Thrips tabaci on Potato SAYED ALI ASGHAR FATHI 1 , ALI ASGHARI† AND MOHAMMAD SEDGHI† Department of Plant Protection and †Plant Breeding, University of Mohaghegh Ardabili, Ardabil, Iran 1 Corresponding author’s e-mail: fathi@uma.ac.ir ABSTRACT Aeolothrips intermedius (Bagnall) and Orius niger (Wolff) feed on larvae-I-II and adults of the onion thrips (Thrips tabaci Lind.) in the potato fields of Ardabil region. Predation by O. niger, one female and one nymph-V and A. intermedius, three adults and three larvae-II, was determined in the separated and combined uses at three densities of larvae-II onion thrips with a aim to investigate the additive effect and intraguild predation of O. niger and A. intermedius in the combined uses and compared with the separated uses at three densities of prey. In the separated uses O. niger, one female and one nymph-V, consumed more prey than A. intermedius, three adults and three larvae-II, at three densities of prey. Predation in the combined uses of O. niger and A. intermedius at the 50 and 100 prey densities were higher compared to the separated uses of each predator alone. These results indicated that at the 50 and 100 prey densities, additive effects were occurred on the mortality of prey when two predators were used synchronously. Whereas predation in the combined uses of O. niger and A. intermedius at the 10 prey density, were not higher than the separated uses of each predator alone. Interaguild predation of O. niger, female and nymph V, on A. intermedius, adults and larvae-II, were observed also at the 10 prey density. The combined uses of O. niger and A. intermedius at high population density of onion thrips compare to low density can be successful in biological control of this pest. Key Words: Interaction; Aeolothrips intermedius; Orius niger; Thrips tabaci; Predation; Potato INTRODUCTION Onion thrips (Thrips tabaci Lindeman) is a major pest of many crops, which transmit TSWV on damaged plants (Van Rijn et al., 1995; Theunissen & Schelling, 1997; Jones, 2005). Its genetic elasticity has enabled it to develop resistance to almost every insecticide applied in the field (Lewis, 1997). Therefore using resistant plants, sticky traps and natural enemies for control of thrips can be useful (Alimousavi et al., 2007; Ranamukhaarachchi & Wickramarachchi, 2007). In the potato fields of Ardabil region, onion thrips is the most frequently found alongwith Aeolothrips intermedius (Bagnall) and Orius niger (Wolff) as major predators of onion thrips and it is found that they feed on larvae-I-II and adults of onion thrips on potato. Therefore O. niger and A. intermedius could be good candidates for biological control of onion thrips on potato. Specific studies on the predation rates of O. niger and A. intermedius in singly and combined use at different densities of onion thrips are limited in scientific literature. Orius species have been proven as effective predators when used for the biological control of onion thrips and Frankliniella occidentalis (Pergande) (Van De Viere & Degheele, 1992; Dissevelt et al., 1995; Deligeorgidis, 2002; Tommasini & Nicoli, 2002; Blaeser et al., 2004). Also Adults and larvae I-II of A. intermedius were found as predator of thrips species specially F. occidentalis and onion thrips (Bournier et al., 1978 & 79; Lacasa et al., 1982; Torres-Vila et al., 1994; Riudavets, 1995). Frequently, Orius species were used in combination with the predatory mites in biological control of thrips (Gillespie & Quiring, 1992; Sanchez et al., 1997; Fejt & Jarosı´k, 2000; Shipp & Wang, 2003). The impact of these combinations on thrips biological control was narrow mainly, because Orius species not only prey on thrips but also on predatory mites, that is intraguild predation. In this study, we tested the hypothesis that intraguild predation and additive effect are present among O. niger, one female and one nymph-V and A. intermedius, three adults and three larvae-II, in the separated and combined uses for the biological control of the onion thrips at three densities. Also we assessed that A. intermedius subjects to predation by O. niger at three densities of prey. These results can be useful in biological control of onion thrips by two predators, O. niger and A. intermedius, in the potato fields. MATERIALS AND METHODS Collecting and rearing of prey and predators. Onion thrips was collected from the potato fields and reared on