© 2006 The Netherlands Entomological Society 179 No claim to original US government works Entomologia Experimentalis et Applicata 119: 179–188, 2006 Journal compilation © 2006 The Netherlands Entomological Society Blackwell Publishing Ltd Differential predation by the generalist predator Orius insidiosus on congeneric species of thrips that vary in size and behavior Stuart R. Reitz 1 *, Joe E. Funderburk 2 & Scot M. Waring 3† 1 USDA-ARS-CMAVE, 6383 Mahan Dr., Tallahassee, FL 32308-1410, USA, 2 University of Florida, North Florida Research and Education Center, 155 Research Rd, Quincy, FL 32351, USA, 3 Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611, USA Accepted: 18 January 2006 Key words: apparent competition, predator–prey interactions, Thysanoptera, Thripidae, Heteroptera, Anthocoridae, biological control, activity budget Abstract We investigated interactions between the generalist predator Orius insidiosus (Say) (Heteroptera: Anthocoridae) and two species of thrips prey, Frankliniella bispinosa (Morgan) and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and interspecific differences in morphology and behavior between these prey species that could contribute to differences in predation by O. insidiosus. Frankliniella occidentalis is significantly larger than F. bispinosa. Frankliniella bispinosa has greater mobility compared with F. occidentalis. When O. insidiosus was offered either F. bispinosa or F. occidentalis as prey in single species trials, there were no significant differences in the number of prey captured. However, O. insidiosus had significantly more encounters with F. bispinosa than with F. occidentalis. In arenas with equal numbers of both species, O. insidiosus encountered and captured F. occidentalis more than F. bispinosa. In large arenas with two pepper plants (Capsicum annuum L.), O. insidiosus preyed on more F. occidentalis than on F. bispinosa. These results indicate that O. insidiosus can prey on both thrips species, but that it preferentially captures F. occidentalis. The greater locomotion and movement of F. bispinosa, perhaps combined with its smaller size, allow it to evade predation by O. insidiosus better than F. occidentalis. Consequently, the observed preference of O. insidiosus for F. occidentalis is not exclusively a function of active selection by the predator but also could arise from inherent differences among prey. We propose this differential predation as a mechanism contributing to observed differences in the temporal dynamics of these species in pepper fields. Introduction Generalist predators can forage on a broad spectrum of prey, yet they may show distinct preferences for particular prey. Thus, generalist predators may capture and consume prey in amounts disproportionate to the overall abundance of potential prey in the environment (Chesson, 1983). Such predation preferences can produce significantly different population dynamics in closely related species of prey and consequently alter community composition (McPeek, 1990; Settle & Wilson, 1990; Gascon, 1992; Blaustein, 1998). Although prey preference implies a predator-based process, the phenomenon of preference can be a function of two processes: active choice by the predator and passive selection by the prey (Pastorok, 1981). These components need not be mutually exclusive, but rather may jointly influence differential predation (Blais & Maly, 1993). Active choice occurs when predators discriminate among prey of different quality (Williams, 1987; Lang & Gsödl, 2001). Active selection factors that can influence preda- tion include size variation among available prey types (O’Brien et al., 1976; Peckarsky, 1980) and differen- tial nutritional quality of various prey to a predator (Eubanks & Denno, 2000; Roger et al., 2000; Mendes et al., 2002). Passive selection is based on intrinsic differences among prey types wherein the prey affects the outcome of encounters * Correspondence: Stuart R. Reitz, USDA-ARS-CMAVE, 6383 Mahan Dr., Tallahassee, FL 32308-1410, USA. E-mail: sreitz@saa.ars.usda.gov † Present address: Department Biology, University of North Carolina, Chapel Hill, NC 27599, USA