Ecological Entomology (2011), 36, 435–441 DOI: 10.1111/j.1365-2311.2011.01286.x Leaf domatia reduce intraguild predation among predatory mites JO ˜ AO A. M. FERREIRA, 1,2 DALYSON F. S. CUNHA, 2 ANGELO PALLINI, 2 MAURICE W. SABELIS 1 and A R N E J A N S S E N 1 1 Section Population Biology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands and 2 Department of Animal Biology, Entomology, Federal University of Vic ¸osa, Vic ¸osa, Brazil Abstract. 1. Although theory suggests that intraguild predation destabilises food webs and may result in exclusion of species, empirical observations of food webs reveal that it is a common interaction. It has been proposed that habitat structure reduces the interaction strength of intraguild predation, thus facilitating the coexistence of species. 2. This was tested using acarodomatia, tiny structures on plant leaves, and predatory mites, which usually reside in these domatia. Sweet pepper plants (Capsicum annuum L.) were used, which possess domatia consisting of tufts of hair, and coffee plants (Coffea arabica L.) with pit-shaped domatia. 3. On sweet pepper, the predatory mites Neoseiulus cucumeris Oudemans and Iphiseius degenerans Berl. feed on each other’s juveniles. Larvae of each of the species were therefore used as intraguild prey with adult females of the other species as intraguild predators. On coffee, a similar set-up was used, with larvae and adult females of Amblyseius herbicolus Chant and Iphiseiodes zuluagai Denmark & Muma as intraguild prey and intraguild predators, respectively. 4. Domatia on detached, isolated sweet pepper and coffee leaves were either closed with glue or left open, after which larvae and adult predators were released. As a control, larvae were released on leaves with open or closed domatia without an adult predator. 5. Survival of larvae was high in the absence of the adult (intraguild) predator. In the presence of the intraguild predator, survival was significantly higher on leaves with open domatia than on leaves with closed domatia. 6. This shows that even such tiny structures as plant domatia may significantly affect the interaction strength of intraguild predation. Key words. Antipredator behaviour, habitat structure, indirect plant defence, Phyto- seiidae, predator–predator interactions. Introduction Intraguild predation, the predation among species that also compete for resources (Polis et al., 1989), is a common interaction in food webs (Polis et al., 1989; Polis & Holt, 1992; Rosenheim et al., 1995; Polis & Winemiller, 1996; Arim & Marquet, 2004). This is at odds with the theory on intraguild predation in well-mixed populations, which predicts Correspondence: Arne Janssen, Section Population Biology, Insti- tute for Biodiversity and Ecosystem Dynamics, University of Amster- dam, Amsterdam, The Netherlands. E-mail: arne.janssen@uva.nl that intraguild predation destabilises food web dynamics and may result in exclusion of species (Polis & Holt, 1992; Holt & Polis, 1997; Morin, 1999; Diehl & Feissel, 2000, 2001; Mylius et al., 2001; Kuijper et al., 2003). Recently, several meta-analyses have shown that the effects of intraguild pre- dation in experimental systems indeed differ from theoretical predictions (Janssen et al., 2006, 2007; Rosenheim & Harmon, 2006; Vance-Chalcraft et al., 2007). For example, experiments often do not show the predicted effects of intraguild pre- dation on lower trophic levels (Janssen et al., 2006, 2007; Rosenheim & Harmon, 2006). It is as yet unclear what causes this discrepancy between theory and experiment.  2011 The Authors Ecological Entomology  2011 The Royal Entomological Society 435