Fred P. Hain

Field Surveys and Evaluation of Native and Established Predators of the Hemlock Woolly Adelgid (Homoptera: Adelgidae) in the Southeastern United States

Abstract There has been little research conducted on the effects of native or established predators on populations of the hemlock woolly adelgid, Adelges tsugae Annand. This study used field surveys and cage exclusion experiments to examine the relationship between established predators and A. tsugae in the southeastern United States. Predators were collected in very low densities in both years. Harmonia axyridis Pallas (Coleoptera: Coccinellidae), lacewings (Neuroptera: Chrysopidae and Hemerobiidae), and gall gnats (Diptera: Cecidomyiidae) represented 81% of the total predators collected in 1998. Cage exclusion experiments revealed no significant predator effects in all three sites in 1997 and 1998. It is unlikely that established predators are exhibiting any significant control on adelgid populations because of the low densities of predators that were encountered at a time when adelgids were abundant. Therefore, controlled releases of non-native predators into these sites should be considered.

Hemlock woolly adelgid (Adelges tsugae) infestation affects water and carbon relations of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana)

Hemlock woolly adelgid (HWA) is an exotic insect pest causing severe decimation of native hemlock trees. Extensive research has been conducted on the ecological impacts of HWA, but the exact physiological mechanisms that cause mortality are not known. Water relations, anatomy and gas exchange measurements were assessed on healthy and infested eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlock trees. These data were then used in a mechanistic model to test whether the physiological responses to HWA infestation were sufficiently significant to induce changes in whole-plant water use and carbon uptake. The results indicated coordinated responses of functional traits governing water relations in infested relative to healthy trees. In response to HWA, leaf water potential, carbon isotope ratios, plant hydraulic properties and stomatal conductance were affected, inducing a reduction in tree water use by > 40% and gross primary productivity by 25%. Anatomical changes also appeared, including the activation of traumatic cells. HWA infestation had a direct effect on plant water relations. Despite some leaf compensatory mechanisms, such as an increase in leaf hydraulic conductance and nitrogen content, tree water use and carbon assimilation were diminished significantly in infested trees, which could contribute to tree mortality.

Defensive mechanisms of loblolly and shortleaf pine against attack by southern pine beetle,Dendroctonus frontalis Zimmermann, and its fungal associate,Ceratocystis minor (Hedgecock) Hunt

Loblolly and shortleaf pine growing on a single site in the North Carolina piedmont were examined to determine similarities and differences in their defensive mechanisms against the southern pine beetle,Dendroctonus frontalis Zimmermann, and its fungal associate,Ceratocystis minor (Hedgecock) Hunt. Both species responded to wounding and fungal inoculation by forming a hypersensitive lesion around the wound site. There were significantly less soluble sugars and more monoterpenes in the lesion tissue than in unwounded inner bark. The two species were similar in resin flow rate and inner bark soluble sugar content, but the loblolly pines had thicker bark, longer hypersensitive lesions, and a higher concentration of inner bark monoterpenes. Inner bark monoterpene composition was also significantly different between the two pine species. It is hypothesized that two different defensive strategies against southern pine beetle attack may be utilized.

Toxicity of host monoterpenes to Dendroctonus frontalis and Ips calligraphus (Coleoptera: Scolytidae)

The toxicity of four monoterpenes present in loblolly (Pinus taeda L.) and shortleaf (P. echinata Mill.) pine to Dendroctonus frontalis Zimmermann and Ips calligraphus (Germar) (Coleoptera: Scolyti...

Balsam woolly adelgid (Homoptera: Adelgidae) and spruce-fir decline in the southern Appalachians: assessing pest relevance in a damaged ecosystem

Research on tree decline has shown that the proportion of sapwood area to heartwood area is an important measure of tree health. Infestation by the balsam woolly adelgid (BWA), Adelges piceae (Ratz.), causes the formation of abnormal wood, which is thought to conduct sap poorly. BWA infestation is also associated with lower (more negative) xylem pressure potentials and increased areas of heartwood. We hypothesize that lower pressure potentials (a consequence of abnormal wood production) increase the rate of cavitation (gas-filling) of sapwood tracheids, thereby accelerating heartwood formation. If this hypothesis is correct, adelgid attack causes loss of functional sapwood both directly and indirectly. There is evidence that the balsam woolly adelgid is an important factor causing the decline of Fraser fir, Abies fraseri (Pursh) Poiret, in the southern Appalachians. However adelgid damage is probably interacting with many other environmental factors to cause reductions in per cent sapwood area. Determining the relevance of this pest to tree decline can be accomplished by examing the relationship that exists between adelgid infestation, increment growth, and per cent sapwood area.

Indices of tree susceptibility to bark beetles vary with silvicultural treatment in a loblolly pine plantation

Abstract We evaluated the effects of thinning and fertilization on eight indices of susceptibility to insects in loblolly pine trees ( Pinus taeda L.) growing in a 24-year-old plantation in eastern Virginia, U.S.A. Resin flow rates, starch concentratons in phloem, an index of relative growth, and bark and phloem thickness all were greater in trees in thinned plots than in control or fertilized plots. Resin flow and starch concentrations varied seasonally. Bark electrical resistance values were greater in the control and fertilized treatments. Based on association of stocking densities with bark-beetle-induced mortality, thinning is often recommended as a silvicultural treatment to reduce susceptibility of forest stands to insects. This study demonstrates that thinning affects many of the biochemical and physical characteristics of loblolly pine that have been suggested as predictors of host susceptibilityto bark beetles.

The Influence of Self-Marking With Fluorescent Powders on Adult Bark Beetles (Coleoptera: Scolytidae)

Under laboratory conditions, Dendroctonus frontalis Zimmermann and Ips grandicollis (Eichhoff) adults became self-marked with fluorescent powders upon emergence from treated logs. The technique pro...

Predation of Gypsy Moth (Lepidoptera: Lymantriidae) Pupae in Three Ecosystems Along the Southern Edge of Infestation

Abstract The predation potential of small mammals, in particular mice, Peromyscus spp., and invertebrates, was evaluated from 1992 to 1995 near the leading edge of gypsy moth, Lymantria dispar (L.), spread into the southeastern United States. Two study sites were established in each of three geographic areas: the coastal plain, Piedmont, and mountains. All sites were mixed hardwood stands with varying amounts of oak, Quercus spp., and all were classified for gypsy moth susceptibility. Small mammal density was estimated using Sherman live-traps and pitfall traps within these 4.68-ha sites in early and late summer. Each site contained 75 trapping stations located on a 25-m grid. Predation was measured by offering freeze-dried gypsy moth pupae near trapping stations at four heights (0, 0.25, 1.0, and 2.0 m) on different tree boles. Pupal predation was monitored for three consecutive nights. Vertebrate predation was positively correlated with good mast production in the previous autumn. Predation data showed that when mice were at high densities they were the major source of pupal predation. However, within these southern sites, when densities of Peromyscus spp. were low, predation by invertebrates was occasionally greater than predation by vertebrates. These data suggest that in some years invertebrates may retard gypsy moth buildup when small mammals are scarce due to mast crop failures.

The Balsam Woolly Adelgid in North America

The balsam woolly adelgid, also known as the balsam woolly aphid, is native to the silver fir (Abies alba) forests of central Europe. The insect was introduced into North America around 1900. Although European firs are not seriously affected by this adelgid, North American firs frequently experience either crown dieback or tree death, or both.

Hemlock Woolly Adelgid in the Eastern United States: What Have We Learned?

Abstract Adelges tsugae (Hemlock Woolly Adelgid) is a small piercing-sucking insect that feeds on Tsuga spp. (hemlock ) trees. Native to Asia and the Pacific Northwest, the Hemlock Woolly Adelgid is invasive in the eastern United States where it attacks Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock). It is currently found in 19 eastern states and has caused extensive mortality to hemlock forests. The ecological and economic impacts of this pest are significant, widespread, and often difficult to quantify. As the Hemlock Woolly Adelgid continues to disperse throughout the range of Eastern and Carolina Hemlocks, management techniques aimed at controlling it are being researched, implemented, and assessed. This introductory paper provides an overview of the biology, life cycle, ecology, and history of this pest in the eastern US as a foundation for this special issue.