Permanent Link: http://ufdc.ufl.edu/IR00002894/00001
 Material Information
Title: Insect Galls
Physical Description: Fact Sheet
Creator: Buss, Eileen A.
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication: Gainesville, Fla.
Publication Date: 2008
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status: Published
General Note: "First printed: October 1993. Revised: June 2008."
General Note: "ENY-331"
 Record Information
Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00002894:00001

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ENY-331 Insect Galls1 E. A. Buss2 1. This document is ENY-331 (MG325), one of a series of the Department of Entomology and Nematology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First printed: October 1993. Revised: June 2008. Please visit the EDIS Website at http://edis.ifas.ufl.edu. 2. E. A. Buss, associate professor, Entomology and Nematology Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label. Use pesticides safely. Read and follow directions on the manufacturer's label. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean Galls occur on many different plants. These growths may be caused by insects, mites, fungi, bacteria, or nematodes, but insect galls are the most common. Gall-forming insects include adelgids, phylloxerans, psyllids, gall midges, and gall wasps. Of the more than 2,000 galling insects in the United States, over l,700 are gall midges or gall wasps. Galls are abnormal growths of plant cells formed in response to egg-laying by adult insects or feeding by immatures. Eggs are usually laid in actively growing plant tissue. The irritated plant tissue quickly surrounds the egg or immature insect, and protects and provides food for the gall-maker until it matures. Gall-makers may live in individual or communal chambers inside the gall. The shape of each gall depends on which insect caused it to form. They may look like tiny blisters, round balls, tubes, or folded leaves. The gall surface may be smooth, hairy, or covered with spines. They may occur anywhere on the plant (e.g., seeds, flowers, petioles, branches, stems, roots), but most galls occur on leaves. More than one type of gall may occupy a plant or plant part. Commonly infested plants are in the families Rosaceae (roses), Asteraceae (asters), Salicaceae (willows), and Fagaceae (oaks). Oaks, however, support the greatest diversity of gall-makers in North America. Gall susceptibility varies greatly between plant species grown under the same conditions. Galling insects are usually not considered pests. Most are harmless and just look interesting. However, certain species can physically or aesthetically damage high value plants by reducing photosynthesis and seed production, discoloring foliage, changing plant architecture, causing defoliation, branch dieback, and rarely, plant death. Gall Wasps (Hymenoptera: Cynipidae) Gall wasps (Figure 1) have unusual life cycles. Wasps of the two generations often look physically different, and may attack the same or different plant structures and make very different galls. As a result, the wasps of both generations have occasionally been falsely described as separate species. One generation is usually all female and the other has both males and


Insect Galls 2 females. Adult gall wasps are small (1/16-1/4 inch long). Larvae are about 1/16-3/16 inch long, white, and lack legs. Larvae pupate inside the galls, and adults chew circular holes in the galls upon emergence (Figure 2). One generation may last from several months to three years. Figure 1. Adult gall wasp (Diplolepis rosae) which develops in the mossy rose gall. Credits: J. Shorthouse, Laurentian University Figure 2. Gall wasp adult inside a leaf gall. Credits: J. Castner, University of Florida Gall Midges (Diptera: Cecidomyiidae) Gall midges are tiny, delicate flies (3/32-1/8 inch long) (Figure 3). Larvae are legless (1/16-1/4 inch long), and white, yellow, or red in color. The larval stage may last from two weeks to more than two years. Feeding damage is only caused by the larvae, which suck plant juices inside galls. Some larvae pupate within their galls, while others exit the galls and pupate in the soil. Subsequent adult activity is timed to the host's biology, often coinciding with budbreak in the spring. Female gall midges may be attracted to host chemicals and physical plant characteristics (ie., leaf hairiness). Most gall midges are host-specific. The galls may be spherical (Figure 4) or resemble thorns. Figure 3. Adult gall midge. Credits: R. Gagne Figure 4. Galls formed by gall midges on goldenrod. Credits: L. Buss, University of Florida Aphids (Hemiptera: Aphidae) Aphids are pear-shaped, soft-bodied insects. Individuals of some species are covered with waxy threads, and the wings are held roof-like over the adult's body. They form galls on many plants, petioles, leaves, or twigs, depending on the species. Many aphid gall-makers use different plant genera for winter and summer hosts. Galls occur more frequently on the winter hosts, which usually are trees. Galls occur in the spring after overwintering eggs hatch. Two to several generations of aphids develop in the gall, after which winged adults leave the gall in search of summer hosts. Psyllids (Hemiptera: Psyllidae) Psyllids, or jumping plantlice, are small (3/32-1/4 inch long) and resemble miniature cicadas. Little is known about their biology. Galls typically look like rolled leaves (Figure 5), buttons, or cones, and some waxy powder may be present. Species of Pachypsylla make galls on hackberry. Figure 5. Psyllid gall on a wild lime leaf. Credits: L. Buss, University of Florida


Insect Galls 3 Phylloxerans (Hemiptera: Phylloxeridae) Phylloxerans are related to aphids and psyllids. However, adults hold their wings flat over the body. These insects do not produce waxy threads, but some species are covered with a waxy powder. Their life cycles are often very complex. Galls often appear as small blisters on leaves (Figure 6). Figure 6. Pecan leaf phylloxera galls. Credits: R. Mizell, University of Florida Biological Control Most gall-makers have a complex of natural enemies (parasitoids, predators, pathogens) that suppress their populations. However, natural enemies need some time to catch up with increasing gall-maker numbers. In addition to attacking gall-makers, some of the adult parasitoids and predators may also feed on pollen or nectar for extra energy. Galls are good nutrient sources, so other insects may feed on them or use the gall for shelter. Some of these insects can also kill some or all of the gall-makers. The gall invaders may include gall wasps that cannot form their own galls, gall midges, clearwing borers, longhorned beetles, metallic wood-boring beetles, weevils, ants, and others. Some of these opportunistic insects may also be pests on other plant species. Cultural Control Pruning and destroying infested plant parts is an effective, but labor-intensive, way to minimize gall problems. Without pruning, leaf galls will either drop off with the leaves or jump off by themselves. However, those on the branches, roots and stems of trees may persist for several years. Host plant selection is important, but more work is needed to identify resistant plant varieties and species to certain gall-makers. Gall susceptibility is likely linked to a plant's genetics and age. In general, galls are more likely to form on actively growing plant parts. Maintain normal fertilization, irrigation, and other approved practices to keep plants healthy. Chemical Control Because most gall-makers don't physically damage plants, chemical control is not recommended. But, if populations are a problem, either target the adult gall-makers before they lay eggs (often at bud break) with a contact insecticide or target the immatures inside young galls with a systemic. Correct timing is important for either tactic. Monitor adult activity by placing sticky traps near the galls, and dissect several galls a week to track insect development. Watch the plant's development, too. Most galling insects are in tune with plant phenology. Contact insecticides such as carbaryl (Sevin), and any pyrethroid insecticide may be effective against adults. Systemic insecticides (e.g., Orthene, Avid, Merit) may kill developing insects in leaf galls, but likely won't affect insects in stem galls. A horticultural oil can control aphid galls. Treatments may be applied as high pressure sprays, soil drenches, or trunk injections of highly concentrated insecticides. Drift and nontarget exposure can be problems using sprays. For more information: Hackberry petiole gall psyllid (http://edis.ifas.ufl.edu/IN214) Citrus gall midge (http://edis.ifas.ufl.edu/IN162) Blueberry gall midge (http://edis.ifas.ufl.edu/IN458) Erythrina gall wasp Pest Alert (http://www.doacs.state.fl.us/pi/ enpp/entolgallwasp.html) Insect Galls of Florida (SP343), IFAS Extension Bookstore.