Ambulatory responses of Laricobius nigrinus (Coleoptera:Derodontidae), a hemlock woolly adelgid predator, to odors from prey, host foliage, and feeding conspecifics

Behavioral interactions between insects and their environments are often mediated by volatile cues. Plant-produced chemical cues induced by herbivore activity are often more effective at attracting predators than are cues produced by the herbivore alone (Dicke and van Loon 2000). The presence of herbivore-induced plant volatiles makes foraging by predators more efficient than undirected hunting (Dannon et al. 2010), presumably because they indicate the presence of prey. Just as it is common for predators to find prey using olfactory cues, they can also use chemical cues to avoid intraguild competition or aggression (Janssen et al. 1995; Cakmak et al. 2006, Flowers et al. 2007), and evidence suggests that avoidance is a common response to the reception of a conspecific cue from a particular location (Janssen et al. 1995; Stout and Goulson 2001; Gnanvossou et al. 2003). Understanding these interactions may be important to the implementation of a biological control program in which a natural enemy complex is released and established, because they are integral to how predators find their hosts (Flowers et al. 2007). Information about predator interactions can inform the optimal release density of agents on the landscape and increase the efficiency and effectiveness of programs. Classical biological control practices are being implemented in the eastern United States (U.S.A.) to control on invasive hemlock woolly adelgid (Hemiptera:Adelgidae, Adelges tsugae) populations on eastern hemlock (Tsuga canadensis (L.) Carriere) and Carolina hemlock (Tsuga caroliniana Engelmann) (DeBach 1974; McEvoy 1996; McDonald 2010). Laricobius nigrinus Fender (Coleoptera: Derodontidae) is an adelgid predator associated with hemlock woolly adelgid on western hemlock (Tsuga heterophylla (Raf.) Sarg.) in the northwestern U.S.A. (Kohler et al. 2008) and British Columbia, Canada (Zilahi-Balogh et al. 2002). This predator is considered a promising candidate agent for biological control of hemlock woolly adelgid on eastern hemlock (Mausel et al. 2012). The objective of this study was to determine whether field-collected L. nigrinus responded to host and prey odors in an olfactometer, and to observe whether adding a conspecific individual feeding on hemlock woolly adelgid on host foliage would alter the orientation preferences of L. nigrinus. In 2011 and 2012, Laricobius adults were field collected in the vicinity of Banner Elk, North Carolina, USA. (36.165643°N, 81.872118°W). Eastern hemlock foliage infested with hemlock woolly adelgid was obtained from trees near the Laricobius collection sites described previously, whereas uninfested eastern hemlock foliage was collected in South Burlington, Vermont, USA (44.4669° N, 73.1714° W). All clipped foliage was similarly handled and stored until used in the bioassays. Two behavioral bioassays, conducted in the winters of 2011 and 2012, were used to test the ambulatory responses of adult L. nigrinus to various stimuli in a four-chambered olfactometer (Analytical Research Systems, #OLFM-4-C-2440PE, Gainesville, Florida, USA) identical to the one described in Wallin et al. (2011). One of the following four stimulus treatments was assigned to each glass chamber, which in turn was attached to a randomly chosen arm of the olfactometer: a 84 J. ENTOMOL. SOC. BRIT. COLUMBIA 112, DECEMBER 2015