Adelges tsugae

Adelges tsugae Annand An infested branchlet Closer view I Closer view II Extremely close view Thinning crown Dead trees I Dead trees II Infestation map Hemlock woolly adelgid The Asian hemlock woolly adelgid was first reported in the 1920s, when it was observed attacking western hemlock (Tsuga heterophylla) in the Pacific Northwest (Annand, 1924). A separate introduction established the pest in Virginia, where it spread to attack eastern and Carolina hemlocks (T. canadensis and T. caroliniana; USDI NPS EIS, 2000). The insect feeds on the contents of parenchyma cells that comprise the xylem rays, and a toxin may be involved in causing the needles to prematurely drop (Young et al., 1995). Eastern and Carolina hemlock populations can die from severe infestations. Extensive decline and mortality has occurred in Virginia, Pennsylvania, New Jersey, and Connecticut within ten years of the first detection (Orwig & Foster, 1998). At Shenandoah National Park in Virginia, where hemlock woolly adelgid has been present since 1988, less than 10% of hemlocks sampled still have 90-100% of foliage intact; very few stands are entirely free of the adelgid (Barr, 2002). Hemlock populations in Connecticut were infested in 1985, and mortality ranged up to 95% in the sample stands studied (Orwig & Foster, 1998). Hemlocks play an important ecological role in riparian communities by creating distinctive microclimates, which are important habitats for a variety of wildlife. In northern New Jersey, 96 bird and 47 mammal species are associated with hemlock forests (USDI NPS EIS, 2000). These forests shelter more than 12 species of small mammals, more than 14 species of amphibians and at least 152 species of terrestrial invertebrates. Salamanders, in particular, depend on the unique habitat under a hemlock canopy (Brooks, 2001). Hemlock-lined streams also keep water temperatures cool enough for brook trout (USDI NPS EIS, 2000). According to the National Park Service (USDI NPS EIS, 2000) decline of hemlock in the Delaware Water Gap National Recreation Area is likely to have "massive adverse effects on the ecological, aesthetic, and recreational values of the park." Affected streams would be warmer, have lower water flows, and are more likely to dry up during summer droughts. Overall species diversity in hemlock-dominated habitats would probably decline by 35% or more. Decaying and downed trees would increase debris flow, interfere with water flow, and cause channel scouring that would raise the chance of extreme flood damage. Nutrient cycling would also be disturbed (Jenkins et al., 1999). Spraying of insecticides to control hemlock woolly adelgid will not be effective or very easy in many cases, in part because riparian habitats are often difficult to access completely, and also because of the special concerns in the use of insecticides near watercourses. In the last decade there has been a significant amount of research conducted on the biological control of the adelgid through natural predators and introductions of predators from Asia (McClure, 1995; Wallace & Hain, 2000; Lu & Montgomery, 2001; Zilahi-Balogh et al., 2002). The greatest restoration challenge may be to reintroduce hemlock into former sites. Little is known about hemlock genetics and diversity, and there are no seed orchards of eastern or Carolina hemlocks to provide seed. Reintroduction efforts will be forced to use non-local seed with no information on the effects of seed movement on growth and survival. In addition, virtually nothing is known about post-planting requirements of hemlock seedlings. While the present work is encouraging, a complete solution to this exotic pest problem still appears to be distant. Sources Annand, P. N. 1924. A new species of Adelges (Hemiptera, Phylloxeridae). Pan-Pac. Entomol. 1: 79-82. Barr, M. W. 2002. Eastern Hemlock (Tsuga canadensis) Mortality in Shenandoah National Park. Proceedings: Hemlock Woolly Adelgid in the Eastern United States Symposium, February 5 - 7, 2002, East Brunswick, New Jersey. Brooks, R. T. 2001. Effects of the removal of overstory hemlock from hemlock-dominated forests on eastern redback salamanders. For. Ecol. Managem. 149: 197-204. Jenkins, J. C., J. D. Aber, and C. D. Canham. 1999. Hemlock woolly adelgid impacts on community structure and N cycling rates in eastern hemlock forests. Can. J. For. Res. 29: 630-645. Lu, W. H., and M. E. Montgomery. 2001. Oviposition, development, and feeding of Scymnus (Neopullus) sinuanodulus (Coleoptera: Coccinellidae): a predator of Adelges tsugae (Homoptera: Adelgidae). Ann. Entomol. Soc. Amer. 94: 64-70. McClure, M. S. 1995. Diapterobates humeralis (Oribatida: Ceratozetidae) - an effective control agent of hemlock woolly adegid (Homoptera: Adelgidae) in Japan. Environ. Entomol. 24: 1207-1215. Orwig, D. A., and D. R. Foster. 1998. Forest response to the introduced hemlock woolly adelgid in southern New England, USA. J. Torrey Bot. Soc. 125: 60-73. United States Department of Interior National Park Service Northeast Region 2000. Environmental Assessment for the Release and Establishment of Pseudoscymnus tsugae (Coleoptera: Coccinellideae) as a Biological Control Agent for Hemlock Woolly Adelgid (Adelges tsugae) at Delaware Water Gap National Recreation Area. Wallace, M. S., and F. P. Hain. 2000. Field surveys and evaluation of native and established predators of the hemlock woolly adelgid (Homoptera: Adelgidae) in the southeastern United States. Environ. Entomol. 29: 638-644. Young, R. F., K. S. Shields, and G. P. Berlyn. 1995. Hemlock woolly adelgid (Homoptera, Adelgidae) - stylet bundle insertion and feeding sites. Ann. Entomol. Soc. Amer. 88: 827-835. Zilahi-Balogh, G. M. G., L. T. Kok, and S. M. Salom. 2002. Host specificity of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a potential biological control agent of the hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae). Biol. Control 24: 192-198.