Insect Profiles: Eastern Pineshoot Borer (Eucosma gloriola)
Eastern pineshoot borer (Eucosma gloriola), also known as the white pine tip moth, American pine shoot moth, white pine shoot borer, and Tordeuse americaine du pin, is a small moth that infests various conifers. The damage induced by the insect’s feeding can permanently alter the branch architecture of infested trees. While this seldom results in tree mortality, successive infestations can deform tree crowns. Eastern pineshoot borer was first discovered in Connecticut in 1930. In 1957, the insect was observed infesting white pines near Reading, Pennsylvania. It has since become widespread across much of the United States and eastern Canada.
Distribution & Habitat
Eastern pineshoot borer’s distribution encompasses the range of its hosts. It occurs throughout eastern Canada, and much of the United States, from New England, south to Virginia, and west to Minnesota.
Eastern white, red, and Scotch pine are the insect’s preferred hosts. Austrian, jack, mugo, Swiss mountain, and pitch pine, all 2 and 5 needle pines, and white spruce are also commonly infested. Douglas-fir is occasionally infested. Trees that have been weakened by environmental stressors, disease, or other infestations are more prone to infestation. Trees that are 3 to 8 feet tall generally incur the most damage.
The eggs laid by eastern pineshoot borer are flattened, and pale yellow in coloration. They typically measure around 0.3 mm in diameter. They are circular to slightly elliptical in form. The larvae are initially pale gray to tan, with yellow-brown heads that have a distinct black dot in the center. When mature, the larvae can reach up to 13 mm in length. The pupa are brown. The adults are tiny moths, with two gray bands trailing across a pair of red forewings. The hindwings are gray-brown. The moths have a wingspan of around 1.5 cm.
Eastern pineshoot borer produces one generation per year. Depending on the geographic location, the adults emerge from late April to early June. The adults are nocturnal. During the day, they conceal themselves between needles. Once night falls, the adults mate. After mating, the males expire. Over the next 24 weeks, the females deposit eggs individually or in small groups on twigs and needle sheaths. The eggs hatch in 2 to 3 weeks, revealing masses of larvae. The larvae penetrate nearby shoots, entering behind the needle fascicles, and boring directly into the pith. The larvae feed in the pith for 45 to 55 days, constructing tunnels that extend 7 to 29 cm in diameter.
The larvae are solitary feeders. At first, they progress downward toward the base of the shoots. However, as they mature, the larvae reverse their direction, and begin moving backward, expanding the tunnels as they do so. As the larvae feed, they reduce the pith to pellets of frass that become tightly packed on either side of the tunnels. The larvae generally complete their development by late June. By this time, the shoots may be girdled internally, near the base. Once mature, the larvae chew oblong to oval exit holes 5 to 10 cm above the base of the tunnels. Upon vacating the shoots, the larvae descend to the ground, and weave silken cocoons in the leaf litter, and soil. Within two days, the larvae commence pupation. They remain dormant for the winter months, and appear as adults the following year.
Symptoms of Infestation
The damage induced by the larval feeding is seldom severe, but persistent attacks over several years can cause leaders to become stunted or forked. This can result in trees assuming a malformed appearance. In the year following the initial infestation, trees may be devoid of new growth. New shoots that expand will become discolored, eventually turning red. The larval feeding will cause thinner shoots to wilt. In fall and winter, the abandoned shoots will frequently bend or break off at the girdled section, with only short stubs remaining. If the shoots are cut open, they will reveal straight tunnels packed with frass. If opened prior to July, the larvae may be found feeding within the shoots.
- To determine if eastern pineshoot borer is present, inspect potential hosts for exit holes in summer.
- Maintain trees through sound cultural practices. Ensure that trees are sufficiently watered, especially during periods of extended drought. Each year, apply a layer of organic mulch around the base of susceptible trees to improve the soil quality, moderate the soil temperature, and retain soil moisture.
- Larvae that bore into small or narrow shoots may chew into the vascular tissue, and be smothered by the ensuing pitch flow.
- Eastern pineshoot borer has several natural parasites that help to reduce its populations. The most effective is the Ichneumon wasp, Glypta sp.
- Insecticides registered for use on eastern pineshoot borer can provide some control when populations are abundant. Applications should be performed in late spring or early summer, before the larvae infiltrate the shoots.
Photo courtesy of the Government of Canada