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Acrosternum hilare

(Hemlock Woolly Adelgid)

Overview

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Insect. Adelges tsugae is a small, aphid-like insect that has become a serious pest of eastern hemlock and Carolina hemlock. The most obvious sign of infestation is the presence of white, woolly egg masses on the underside of hemlock needles . Infested eastern North American hemlocks defoliate prematurely and will eventually die if left untreated. A. tsugae is a difficult insect to control because the white waxy secretion protects it from pesticides. It is dispersed to new habitats through the nursery trade and locally by wind, birds, mammals, and humans. Hemlock trees provide important habitats for many wildlife species and A. tsugae has severe adverse ecological impacts on an that habitat which will become more severe as its distribution expands

Interesting Facts

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Common Names

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Common Names in English:

Green Stink Bug, Hemlock Woolly Adelgid, Hemlock Wooly Adelgid

Description

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Physical Description

Species Acrosternum hilare

A. tsugae is a small ( 0.74 mm ), reddish-purple, aphid-like insect that covers itself with a white, waxy secretion. Both winged and wing-less forms are present. Their mouthparts are thread-like and about 1.5 mm long and used to suck sap . Eggs are brownish-orange but darken as the embryo matures . When the eggs hatch , reddish-brown//// crawlers move about actively in search for a suitable site to settle. The tiny crawlers can only be seen with a hand lens because they are barely visible to the naked eye. Once the crawlers settle, they insert their mouthparts into the plant at the base of the hemlock needles and remain in the same place for the duration of their life. Dormant first instar nymphs are black with a white fringe around the edge and down the center of the back. The developing nymphs produce white, cottony , waxy tufts that cover their bodies. The white masses are 3 mm or more in diameter. The presence of these masses on the twigs and bark of hemlock is a sure sign of A. tsugae.

Habitat

The secondary host of A. tsugae is hemlock, with spruce being the primary host where the sexual cycle occurs. Experts hope that an aversion to cold weather will slow or stop its northern movement. In New Jersey and Connecticut, a large population died because of a cold snap in the winter of 2000.

Biome: natural forest , riparian zones, urban areas

Ecology: A. tsugae is damaging hemlock ecosystems in eastern North America where both eastern and Carolina hemlock serve as hosts. To date, approximately 25 percent of the 1.3 million hectares of host type has been infested. The entire range of eastern hemlocks is at risk within the next 20 to 30 years. Immature nymphs and adults damage trees by sucking sap from the twigs . The tree loses vigor and prematurely drops needles , to the point of defoliation , which may lead to death . If left uncontrolled, the adelgids can kill a tree within three to four years. Trees of all sizes and ages are attacked, but natural stands of hemlock are at greatest risk for death. The value of ornamental hemlocks is reduced by the presence of the dirty, white woolly masses attached to the twigs or base of needles. Eastern hemlock is economically important in several areas of the eastern United States. The nursery industry in North Carolina and Tennessee currently maintains approximately $34 million in hemlock growing stock. This industry is feeling the effects of A. tsugae in reduced sales of native hemlock for ornamental use. The impact of this insect on the wood products industry of the northeastern U.S. could be substantial. Hemlock trees are ecologically important and provide a unique environment. The lifespan of an eastern hemlock can reach 900 years, and this tree is a component of many old growth communities. The hemlock forest also provides nesting sites and foraging habitat for neotropical migratory bird species. Several threatened or endangered species of flora and fauna require hemlock forests to survive. These forests are normally stable and resistant to plant invasions, so the loss of hemlocks from such forests will greatly affect the microclimate and soil conditions. Large-scale hemlock die-offs will affect species diversity , vegetation structure, stand environmental conditions , and ecosystem processes. For example, lepidopterans, like Semiothisa fissinotata, which feed solely on hemlocks, will be affected.

Biology

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Diet

Feed on developing seed of many hosts including trees , shrubs , vines , weeds and many cultivated crops . They may also feed on the stems and foliage when seed are not present. Both nymph and adult stink bugs pierce plants with their needlelike mouthparts and suck sap from pods, buds, blossoms and seeds. The degree of damage depends on the developmental stage of the plant when it is attacked. Immature fruit and pods become deformed as they develop. Seeds are often flattened and shriveled. Germination can be reduced, or the seeds may fail to germinate at all.

Reproduction

A. tsugae has both sexual and asexual (parthenogenic) reproduction . The asexual cycle occurs on hemlock while the sexual stage occurs on spruce. A. tsugae has two asexual generations per year on hemlock. Each adult can produce between 50-300 eggs within her lifetime. A. tsugae's reproductive output and its lacks of natural enemies has caused populations to explode in North America.

Spring generation adults lay numerous eggs within large, white, woolly sacs . The eggs hatch and crawlers from the second generation move to attach themselves to new needles . Once they find a site, they settle in and become dormant (no feeding) until fall . At that time, they break dormancy and begin to feed and develop through the fall and winter. A. tsugae is atypical of most insect species in that it is inactive for much of the growing season and very active throughout the winter.

Taxonomy

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Notes

Name Status: Accepted Name . Latest taxonomic scrutiny: 24-Jun-1996.

Similar Species

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Members of the genus Acrosternum

ZipcodeZoo has pages for 14 species and subspecies in this genus:

A. arabicum · A. graminea · A. heegeri · A. herbidum · A. hilare (Hemlock Woolly Adelgid) · A. hilaris · A. impicticorne · A. istum · A. malickyi · A. marginatum · A. millierei · A. pennsylvanicum · A. rubescens · A. ubicum

More Info

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Further Reading

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Notes

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Contributors

Identifiers

Last Revised: 7/2/2009