Sucking Insects/True Bugs
Aphids and Adelgids
Forest Health Guide for Georgia Foresters
Written by Terry Price, Georgia Forestry Commission
Adapted for the web by the Bugwood Network
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Aphids and adelgids are grouped in the insect suborder Homoptera and are closely related species. Many species of aphids are common throughout the forest but the damage done is not considered a forest threat. Aphids appear to favor drought conditions. Pine seedlings growing on dry sites sustain a higher level of aphid attack than trees growing on good to marginal sites. However, damage is considered secondary to drought and control is best achieved by natural means. Chemical control of aphids in forest plantings is not necessary. A black sooty mold develops on trees as a result of aphid secretions (Figure 95). These fungi help entomologists diagnose the occurrence of aphids and other sucking insects.
Adult aphids are small, 1/32 to 1/4 inch, soft-bodied, pear-shaped insects varying in color from red, yellow, green, blue, brown, gray, or black (Figure 96). Adults may be winged or wingless. Most species have a pair of tube-like cornicles arising from the top of the 5th or 6th abdominal segment. Legs and antennae are well developed. Nymphs resemble the adults but lack wings and are smaller. Eggs are usually black and rather large considering the small size of the adult.
Many aphids have a complex life cycle. Most species spend the winter in the egg stage. The eggs hatch in the spring into wingless females. These females reproduce parthenogenetically (without males) and give birth to living young. Several generations may be produced in this fashion, with the first generation or two consisting of wingless individuals and winged individuals appearing later. When the winged individuals appear they usually migrate to a different host plant and reproduction continues. Later in the season the aphids will migrate back to the original plant host where a generation of both males and females is produced. The males and females mate and these females lay the eggs that overwinter.
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Figure 95
photo by R. Scott Cameron |
Figure 96
photo by Herbert A. "Joe" Pase III |
Figure 97
photo by Terry Price |
Aphids suck plant juices from foliage and bark of young twigs and stems. Needles will turn yellow and may curl and become deformed. Aphids also excrete large quantities of honeydew that may drop from the trees onto cars and other objects below. Honeydew is simply the sap that is sucked in through the beak and only partially digested and excreted. This honeydew is sweet and sticky and often forms on the branches, foliage and twigs upon which sooty molds grow. Ants commonly feed on these sweet excretions. Certain species of ants are often seen scraping the outer bark over which aphid secretions have formed. The bark has a unique appearance (Figure 97).
Common Aphid Species on Conifers
The white pine aphid, Cinara strobi, is a common pest occurring on white pines. Young trees, recently transplanted trees or individual branches on large trees may be killed. The body is shiny dark brown with a white stripe extending down the middle of the back, and white powdery spots on the sides (Figure 98). In the fall, winged females lay eggs. The shiny black eggs are laid end to end in a straight line with an
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average of about 6 per needle. Hatching occurs in the spring and the wingless females produce living young. Later in the season winged females are produced which migrate and also produce living young. In the fall, winged males and females mate and lay the eggs that overwinter.
The pine bark aphid, Cinara atlantica, congregates in large masses on the branches of southern pines (Not Pictured). Sap is sucked from the phloem of branches and twigs. It occurs statewide and is a nuisance during the Christmas season when brought in homes via Christmas trees. Many homeowners think this aphid is a tick and to the casual observer may appear as such.
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Figure 98
photo by William H. Hoffard |
Adelgids
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These insects are often confused with aphids. They are related to woolly aphids and phylloxerans but occur exclusively on conifers. Adelgids feed on foliage, twigs, limbs and trunks. Galls are produced on some hosts and can be used to identify the species of adelgid (Figure 99). Their life cycle is very complicated and is confounded by sexual and asexual reproduction as well as alternate hosts.
Some adelgids resemble aphids and others are quite unique. Identification is confirmed by the host plant and the production of a white secretion that may be powdery, filamentous or ribbon-like (Figure 100).
Adelgids insert their long, hairlike, mouthparts through the bark into the phloem and begin sucking sap. Soon their bodies are covered with the white excretions. Twigs become swollen and gouty from the feeding. Tree trunks become covered with the white excretions and appear as snow. Some common species are the pine bark adelgid, Pineus strobi, a pest of white pine (Figure 101) and the hemlock woolly adelgid (HWA), Adelges tsugae, a pest of Eastern and Carolina hemlock (Figure 102). The HWA has spread west and south into Georgia. It is currently found in Rabun, Towns, Habersham, White, and Union Counties. The heaviest infestations are in the Chattooga, Little Tennessee, Tallulah, and Hiawassee watersheds. Clemson University and U.S. Forest Service ento-mologists have released three coccinellid beetles at dif-ferent sites in northeast Georgia as a biological control agent.
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Figure 99 - Balsam woolly adelgid damage
photo by David McComb |
Figure 100
photo by Jerald E. Dewey |
Figure 101
photo by Larry R. Barber |
Figure 102 - Woolly material produced by HWA
photo by Robert L. Anderson |
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