Gypsy Moth in the Southeastern U.S.: Biology, Ecology, and Forest
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SREF-FH-008 February 2017 efforts to eradicate the species, it Gypsy Moth in the Southeastern U.S.: Biology, became established throughout eastern Massachusetts. Since then, Ecology, and Forest Management Strategies the gypsy moth has expanded its range throughout the Northeast and Mid-Atlantic regions, west to the Lake AUTHORED BY: BRUCE W. KAUFFMAN, WAYNE K. CLATTERBUCK, States (Minnesota, Wisconsin, and ANDREW M. LIEBHOLD, AND DAVID R. COYLE Illinois), Indiana, Ohio, and into the central Appalachian Mountains (West Virginia and Virginia). Gypsy moth populations have recently established in North Carolina, and moths are an- nually captured in Kentucky and east- ern Tennessee, though no established populations exist (Fig. 1). Adult gypsy moths are occasionally captured in Georgia and South Carolina. Gypsy moth eggs hatch in the spring, and newly hatched caterpillars begin feeding on recently expanded leaves. Gypsy moths can disperse into areas by “ballooning,” whereby newly hatched caterpillars climb into tree crowns and spin down on strands of silk until the wind carries them to other trees (Fig. 2). Caterpillars mostly feed during the night, but may feed during the day when populations are high. Gypsy moth caterpillars are distinct in that they have five pairs of blue spots beginning at the head followed by six pairs of red spots ending at their posterior (Fig. 3), though these spots are less obvious in younger caterpillars. After feeding for about 6-8 weeks (adult moths do not eat - all the eating takes place during the caterpillar life stage), Figure 1. In the southeastern U.S., the gypsy moth is established throughout most of Virginia, and moths are regularly captured in eastern Kentucky, eastern Tennessee, and much of North caterpillars pupate, and emerge Carolina. The Slow the Spread (i.e. Containment) area is a band that extends from northern as adult moths (Fig. 4). Following North Carolina through the Virginias, Ohio, Indiana, Illinois, and north to western Wisconsin / mating, the flightless females lay their eastern Minnesota. The gypsy moth is established in the entire northeastern U.S. eggs in a single mass usually on the side of tree trunks, and especially The European gypsy moth (Lymantria dispar L.) is a non-native insect that was on the undersides of branches. Egg accidentally introduced to North America in 1869 when it escaped cultiva- masses can also be laid on picnic tion by a French amateur entomologist living near Boston, MA. Despite early tables, firewood, automobiles, www.southernforesthealth.net/insects 1 Figure 2. Young gypsy moth larvae can travel Figure 3. Gypsy moth larvae have five pairs Figure 4. Adult female gypsy moths are most- long distances by “ballooning”, where they of blue dots starting just behind the head, ly white and do not fly, and adult males are a produce a long strand of silk that gets carried followed by six pairs of red dots. dull brown color. by the wind. logging equipment, or any other are also important factors limiting when gypsy moth larvae populations object that is stationary. Because of gypsy moth populations. The fungal are low, impacts from NPV are the variation in elevation and latitude pathogen Entomophaga maimaiga, usually only noticeable when larval in the southeastern U.S., timing of originally from Japan, is present populations are high. the gypsy moth life cycle differs throughout the range of gypsy moths depending on location (Fig. 5). in the U.S. and plays a major role in gypsy moth population regulation. Because females do not fly (but This fungus thrives in hot humid Gypsy Moth Hosts see Box 1), established populations environments17, and will likely be spread rather slowly - usually only particularly important should the Gypsy moth caterpillars feed on 5-10 miles per year. Given the gypsy southeastern U.S. become infested the leaves of many woody plants, moth’s broad host range, large with gypsy moth. However, extremely although some species are more portions of the natural and urban dry weather is often associated with susceptible than others. The major environments throughout the eastern increased adult gypsy moth captures, factor associated with susceptible U.S. provide suitable habitat where as fewer caterpillars may be killed by forest stands - those most likely to the species could eventually establish E. maimaiga under these conditions. experience defoliation from a large (Fig. 6). Spread of the gypsy moth A nucleopolyhedrovirus (NPV) can density of gypsy moth caterpillars - is into uninfested regions is facilitated also be an important regulator of the presence of tree species favored by accidental movement of life gypsy moth populations5. Unlike E. by the gypsy moth. Table 1 lists stages, typically by transport of egg maimaiga, which can be present even tree species and their susceptibility masses on objects such as vehicles, nursery stock, firewood, mobile homes, or lawn furniture that are moved long distances13 (Fig. 7). Eastern KY Eastern VA Northern GA Natural enemies can help regulate established gypsy moth populations, especially when populations are at low densities. Small mammal predators, such as the white-footed mouse (Peromyscus leucopus), are known to find and consume gypsy moth pupae, and many different bird species can eat gypsy moth caterpillars5. Insect predators like large caterpillar hunter beetles (Calosoma spp.) readily feed egg caterpillar pupa adult on gypsy moth caterpillars, and parasitoids (usually tiny wasps or Figure 5. Phenology of the gypsy moth in three areas of the southeastern U.S. In general, flies) will use gypsy moth eggs or overwintering eggs hatch in early spring, caterpillars feed for several weeks, spin cocoons and caterpillars as hosts5. Microbes pupate, then emerge as adults in early to mid-summer. www.southernforesthealth.net/insects 2 to gypsy moth defoliation in each spring. Gypsy moth defoliation is of three categories: favored, not Effects of Gypsy Moth especially detrimental because it favored, and avoided. Trees listed on Trees occurs when growth is most active as favored are highly vulnerable. (spring and early summer) and when Vulnerability refers to the likelihood starch reserves are at their lowest of tree mortality if a population One complete defoliation will not levels1. The loss of as much as 50% buildup occurs. The condition or normally kill healthy hardwood trees. of the foliage usually results in little health of the trees in the forest affects Leaves produce the energy required more than a reduction of growth. vulnerability. Trees not favored may for the growth and development However, when more than half of the be fed upon when favored foliage of a tree, and most healthy trees leaves are consumed, the tree cannot is not available. Those trees that are produce more energy than they produce enough energy and other rarely fed upon by gypsy moths are need. The excess energy is stored as resources required for growth, and known as avoided species. Generally, starch in the roots, and the tree uses must subsist on its stored reserves all oaks are favored by gypsy moths, this energy to maintain itself during until new leaves are formed. This and species rarely fed upon include the dormant winter season, and to process, called refoliation, puts a most pines and yellow-poplar. produce buds and twigs the following tremendous strain on the tree and usually results in death of buds, twigs, branches, and feeder roots during the winter months. If no defoliation occurs the following year or two, most trees (except those in poor condition) should survive and regain their former growth and appearance. Defoliation, even at low levels, can be harmful if repeated for several years. Even healthy trees may become stressed and die if they go through the defoliation-refoliation process for two or more years in succession1. When defoliation coincides with drought or other stressors, trees are much more likely to die. Box 1. Asian gypsy moth is very similar to European gypsy moth, but adult female Asian gypsy Gypsy moth outbreaks are cyclic moths can fly. These are occasionally captured in the southeastern U.S., but no established populations exist. and typically last one to three years in oak-dominated stands. Outbreak populations then decline and Table 1. Gypsy moth host preferences (adapted from 7,11) Preference level Description Tree species Favored Species readily eaten or preferred by gypsy Apple, basswood, river and white birch, hawthorn, moth larvae during all larval stages hazelnut,hophornbeam, hornbeam, larch, most oaks, pear, serviceberry, sweetgum, willows, witch-hazel Not Favored Species fed upon by some larval stages American beech, sweet and yellow birch, blackgum, boxelder, buckeyes, when favored or preferred foliage is not butternut, black cherry, chestnut, elms, cottonwood, cucumbertree, available elms, most eucalyptus, hackberry, hemlock, most hickories, locust, most maples, pawpaw, pear, persimmon, most spruces, most pines, redbay, redbud, sassafras, sourwood, black walnut Avoided Species rarely fed upon by gypsy moth Most ash, most azaleas, baldcypress, buckthorn, catalpa, dogwood, larvae eastern redcedar, ginkgo, American holly, horsechestnut, Kentucky coffee-tree, juniper, black and honeylocust, magnolia, mountain laurel, mulberry, rhododendrons, sycamore, most viburnum, water tupelo, yellow-poplar www.southernforesthealth.net/insects 3 collapse because of the buildup of Site quality does not appear to disease, parasitoids, and starvation. directly influence tree mortality Populations often remain low for four following gypsy moth defoliation, to 12 years before increasing again5. but site quality does influence the tree species that grow on a site, which indirectly influences defoliation levels4. Ridgetops and Gypsy Moth Damage steep south- and west-facing slopes are particularly favored by the gypsy With very few exceptions (e.g. moth, because many of the preferred extreme southern Florida, certain tree species occur on these sites. coastal areas in Louisiana and Texas, These are generally drier sites with and parts of the Mississippi River poorer productivity, which may also Figure 7.