Complementary effects of resident natural enemies on the suppression of the introduced moth Epiphyas postvittana Brian N. Hogg ⇑ , Xin-Geng Wang, Karmit Levy, Nicholas J. Mills, Kent M. Daane Department of Environmental Science Policy and Management, University of California, Berkeley, CA 94720-3114, United States highlights " The effects of parasitoids and spiders on an introduced moth were assessed. " The spider appeared to reduce numbers of adult parasitoids. " Both the parasitoid and the spider increased larval mortality of the moth. " Interactive effects of the parasitoid and spider were additive. graphical abstract The combined effects of parasitoids and spiders on moth larvae were additive and did not differ from the sum of their individual impacts, despite possible spider predation on parasitoids. article info Article history: Received 12 July 2012 Accepted 24 October 2012 Available online 2 November 2012 Keywords: Additive effects Intraguild predation Invasive species Predator diversity Predator interactions abstract Generalist predators may disrupt or complement biological control by parasitoids. Past studies have examined how predators and parasitoids interact to affect aphid suppression, but more information is needed from other host taxa. Here, we explore the interactive effects of a spider (Cheiracanthium mildei) and a generalist parasitoid (Meteorus ictericus) on the light brown apple moth (Epiphyas postvittana), a recent introduction to North America. The spider negatively affected adult parasitoids in a field experi- ment, and reduced numbers of parasitized larvae in the laboratory. Nonetheless, the combined effects of parasitoids and spiders on larval mortality of the moth were additive. Percent parasitism was not affected by the presence of the spider in field or laboratory experiments, and results were similar when single or multiple larval instars of the moth were included. The spider’s lack of prey preference for unpar- asitized or parasitized larvae likely precluded any disruptive effects on parasitism. Results suggest that resident generalist parasitoids and predators can work in conjunction to hinder the invasion success of a novel herbivore prey species. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Research attention has increasingly focused on the conse- quences of biodiversity losses for biological control (Straub et al., 2008). Higher diversity within natural enemy communities can enhance herbivore suppression and strengthen positive effects on plants (Snyder et al., 2006). Generalist predators can prey on other natural enemies, however, thus compromising effects on herbi- vores and dampening trophic cascades (Polis and Holt, 1992; Finke and Denno, 2004). An intraguild predator is likely to disrupt herbi- vore suppression if it is an inefficient consumer of herbivores, or if it selectively preys on other predators (Rosenheim et al., 1993). On the other hand, an intraguild predator that efficiently consumes 1049-9644/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.biocontrol.2012.10.008 ⇑ Corresponding author. Address: 137 Mulford Hall, Department of Environmen- tal Science Policy and Management, University of California, Berkeley, CA 94720- 3114, United States. Fax: +1 559 646 6593. E-mail address: hoggbrian@yahoo.com (B.N. Hogg). Biological Control 64 (2013) 125–131 Contents lists available at SciVerse ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon