title: Impact of an Invasive Insect and Plant Defense on a Native Forest Defoliator.
abstract: Eastern hemlock (Tsuga canadensis [L.] Carriére) in the United States is threatened by the invasive hemlock woolly adelgid (Adelges tsugae Annand). The native hemlock looper (Lambdina fiscellaria Guenée) also appears to have played a role in previous population declines of this conifer. Although these two insects co-occur in much of the adelgid's invaded range, their interactions remain unstudied. We assessed looper performance and preference on both uninfested and adelgid-infested foliage from adelgid-susceptible hemlocks, as well as on uninfested foliage from an eastern hemlock that is naturally adelgid-resistant. Larvae reared on uninfested foliage from adelgid-susceptible hemlocks experienced 60% mortality within the first two weeks of the experiment, and pupated at a lower weight than larvae fed adelgid-infested foliage. Despite differences in foliage source, this first look and strong pattern suggests that the hemlock looper performs better (pupates earlier, weighs more) on adelgid-infested foliage. In addition, trends suggested that larvae reared on foliage from the adelgid-resistant tree survived better, pupated earlier, and weighed more than in the other treatments. Larvae preferred adelgid-resistant over adelgid-susceptible foliage. Our results suggest that looper perform slightly better on adelgid-infested foliage and that plant resistance to xylem-feeding adelgid may increase susceptibility to foliar-feeding looper larvae.
authors.affiliation: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA. clairemariahwilson@gmail.com.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Wilson
authors.affiliation: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA. jvendettuoli@gmail.com.
authors.forename: Justin F
authors.initials: JF
authors.lastname: Vendettuoli
authors.affiliation: Harvard Forest, Harvard University, Petersham, MA 01366, USA. orwig@fas.harvard.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Orwig
authors.affiliation: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA. preisser@uri.edu.
authors.forename: Evan L
authors.initials: EL
authors.lastname: Preisser
keywords: herbivore-herbivore interactions; invasive species; plant defense; plant-herbivore interactions