Impact of an Invasive Insect and Plant Defense on a Native Forest Defoliator.

Claire Wilson,Justin Vendettuoli,Evan Preisser,David Orwig

doi:10.3390/insects7030045

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.

Highlights

Trees and other long-lived plants must withstand multiple simultaneous or sequential attacks from an array of herbivores [1]
The eggs were transported in coolers to the University of Rhode Island (‘URI’), where they were reared to pupation on three types of hemlock foliage: uninfested eastern hemlock (‘Susceptible’), adelgid-infested eastern hemlock
(‘Susceptible + HWA’), and material from an individual eastern hemlock tree growing in a forested setting in Sussex County, New Jersey that previous research has found to be highly resistant to adelgid infestation (‘Resistant’; [34,35])

Summary

Introduction

Trees and other long-lived plants must withstand multiple simultaneous or sequential attacks from an array of herbivores [1]. Changes in plant tissues induced by an early-season attacker via plant defense or herbivore offense (sensu [4]) can alter host quantity or quality for subsequent attackers [5,6]. While some of these changes can deter attackers [7], others can increase the fitness of the later-arriving herbivore [8]. Eastern hemlock (Tsuga canadensis [L.] Carriére) is a structurally-dominant and ecologically-important conifer found throughout the eastern United States [13]. As one of the most shade-tolerant conifers in the eastern U.S, T. canadensis has been called a ‘foundation species’

Methods

Results

Conclusion