Galls

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2. Galls are abnormal growths of plant tissue induced by insects and other organisms. Several different groups of insects and one family of mites have developed the ability to induce plant galls. The most important gall-producers are found among the mites, aphids, adelgids, phyloxerans, wasps, and midges.

3. Maple bladder galls are small globular growths on the upper surface of red and silver maple leaves. The galls can be either red or green, and they may occur singly or in clusters.

4. Several tiny mites live inside each gall. The white, carrot- shaped gall mites, barely visible here under high magnification, are invisible to the naked eye.

6. Erineum galls are dense, felt-like patches of plant hairs. On maple, erineum galls are sometimes red, while on alder, beech, and on poplar, they are green or buff-colored. Microscopic gall mites live in among the hairs.

7. Cooley spruce galls are elongated cone-like galls on the new growing tips of Colorado blue spruce. These galls are caused by an adelgid, a close relative of the aphids. Feeding by the adelgid nymphs causes abnormal tissue growth on the twig. Eventually the gall completely encloses them offering protection while they feed inside.

8. Eastern spruce galls are similar except that they occur at the base of new shoots. They are found primarily on Norway spruce, but also on white, red, and Colorado blue spruce.

9. The spruce gall adelgids have interesting but complicated life cycles. Immature females overwinter beneath a wax coat at the base of spruce buds. They mature in the spring and lay eggs on the twigs. Soon after they begin feeding, the galls form around the young nymphs. By midsummer, openings appear on the galls, and the adelgids which have now developed wings fly off to Douglas fir and other spruce trees. On Douglas fir, they go through generations resembling woolly aphids . On this host, their feeding causes yellowish spots and bent needles, but no galls. In the fall, young females may return to their overwintering sites on spruce.

10. A phylloxeran, another aphid-like insect, causes hickory leaf stem gall on the leaves, petioles, and twigs of hickory. A generation of winged phyloxerans develop within the galls. By the end of June, the galls open, and the insects fly off to summer hosts.

11. Oaks have more galls than any other plant. All parts of the tree, including the roots and acorns, can become galled. Horned oak galls are hard, woody swellings on the twigs. Small horns protrude through the surface of the gall, and a small stingless wasp develops in each horn. Horned oak galls and gouty oak gals, which are similar but lack horns, can be destructive pests.

12. A small delicate fly, called a gall midge, lay its eggs in developing dogwood buds. After hatching, their larvae work their way into the tips of the new twigs. Later, the adjacent tissue begin to swell and a gall forms. These are called dogwood club galls.

13. There are dozens of other insect-induced galls in a variety of shapes, colors, and sizes. Each one is the home of one or more immature insects or mites. Controlling gall insects is impractical, and fortunately, the vast majority of galls are not particularly injurious to their hosts. Pruning out heavily galled portions of a plant is sometimes feasible and may help reduce populations of the gall insects. When this is not possible, it is best to accept galls as curiosities of nature.

14. That concludes Part 4, Insects that Produce Galls.

Return to Insects that Produce Galls

	2. Galls are abnormal growths of plant tissue induced by insects and other organisms. Several different groups of insects and one family of mites have developed the ability to induce plant galls. The most important gall-producers are found among the mites, aphids, adelgids, phyloxerans, wasps, and midges.
	3. Maple bladder galls are small globular growths on the upper surface of red and silver maple leaves. The galls can be either red or green, and they may occur singly or in clusters.
	4. Several tiny mites live inside each gall. The white, carrot- shaped gall mites, barely visible here under high magnification, are invisible to the naked eye.
	6. Erineum galls are dense, felt-like patches of plant hairs. On maple, erineum galls are sometimes red, while on alder, beech, and on poplar, they are green or buff-colored. Microscopic gall mites live in among the hairs.
	7. Cooley spruce galls are elongated cone-like galls on the new growing tips of Colorado blue spruce. These galls are caused by an adelgid, a close relative of the aphids. Feeding by the adelgid nymphs causes abnormal tissue growth on the twig. Eventually the gall completely encloses them offering protection while they feed inside.
	8. Eastern spruce galls are similar except that they occur at the base of new shoots. They are found primarily on Norway spruce, but also on white, red, and Colorado blue spruce.
	9. The spruce gall adelgids have interesting but complicated life cycles. Immature females overwinter beneath a wax coat at the base of spruce buds. They mature in the spring and lay eggs on the twigs. Soon after they begin feeding, the galls form around the young nymphs. By midsummer, openings appear on the galls, and the adelgids which have now developed wings fly off to Douglas fir and other spruce trees. On Douglas fir, they go through generations resembling woolly aphids . On this host, their feeding causes yellowish spots and bent needles, but no galls. In the fall, young females may return to their overwintering sites on spruce.
	10. A phylloxeran, another aphid-like insect, causes hickory leaf stem gall on the leaves, petioles, and twigs of hickory. A generation of winged phyloxerans develop within the galls. By the end of June, the galls open, and the insects fly off to summer hosts.
	11. Oaks have more galls than any other plant. All parts of the tree, including the roots and acorns, can become galled. Horned oak galls are hard, woody swellings on the twigs. Small horns protrude through the surface of the gall, and a small stingless wasp develops in each horn. Horned oak galls and gouty oak gals, which are similar but lack horns, can be destructive pests.
	12. A small delicate fly, called a gall midge, lay its eggs in developing dogwood buds. After hatching, their larvae work their way into the tips of the new twigs. Later, the adjacent tissue begin to swell and a gall forms. These are called dogwood club galls.
	13. There are dozens of other insect-induced galls in a variety of shapes, colors, and sizes. Each one is the home of one or more immature insects or mites. Controlling gall insects is impractical, and fortunately, the vast majority of galls are not particularly injurious to their hosts. Pruning out heavily galled portions of a plant is sometimes feasible and may help reduce populations of the gall insects. When this is not possible, it is best to accept galls as curiosities of nature.
	14. That concludes Part 4, Insects that Produce Galls.