This is the first part of a series on summer tree insects. This article examines ailanthus webworm, Asian long-horned beetle, and bagworm.
As spring transitions into summer, temperatures gradually rise, and plants enter the next phase of their development. This period coincides with the appearance of numerous insects, many of which infest vulnerable trees and shrubs. When infestations occur, they can be detrimental to plant health. The following discusses some of the insects that commonly infest plants in summer, and how they impact their hosts.
Ailanthus Webworm (Atteva aurea)
Ailanthus webworm is an ermine moth commonly found throughout the United States. The insect originated in South Florida and the American tropics, where it infested two plants: paradise tree (Simarouba glauca) and Simarouba amara. It has since adapted to a new host plant called tree of heaven. Ailanthus webworm is a member of the bagworm moth family. This refers to the cottony bags that the larvae spin. It is most recognized for its distinct coloration, and unique body. When stationary, the insect resembles a true bug or beetle. When in flight, it appears similar to a wasp. Ailanthus webworm is considered a minor pest in nurseries, and landscape settings, where it causes minor defoliation on host plants.
Ailanthus webworm constructs webs on the leaves of tree of heaven (Ailanthus altissima), an invasive tree species that has been widely introduced and naturalized from China.
Symptoms of Infestation
The life cycle of Ailanthus webworm progresses quickly. Some insects transition to adults within four weeks. This enables Ailanthus webworm to produce many generations each summer, with eggs often laid on the webs of other larvae. As the webs overlap, they become a larger communal web, comprising multiple generations in various stages of their development. The webs are conspicuous on host plants, and can be observed throughout most of the growing season. The insect is a minor defoliator of host plants. While this may temporarily reduce the ornamental value of the host, any consumed foliage is usually replenished within a single growing season.
- Ailanthus webworm is considered a minor nuisance. It does not cause extensive damage to host trees. As such, management of the insect is not required.
Asian Long-horned Beetle (Anoplophora glabripennis)
The Asian long-horned beetle (Anoplophora glabripennis), also known as the starry sky beetle, is a large wood-boring insect native to eastern China, Japan, and Korea. The insect is a small jewel beetle, with a brightly colored body. Though it is innocuous to humans and animals, the Asian longhorned beetle is a destructive pest that is capable of decimating maples and other hardwood trees.
The Asian long-horned beetle infests a wide range of trees, but it is primarily attracted to maples. It affects numerous species, including boxelder, norway, red, sugar, and silver maple. It has also been reported infesting a number of other trees, including birch, elm, horsechestnut, ohio buckeye, and willow. In a few rare instances, it has been discovered in mountain ash, london planetree, poplar, and mimosa.
Symptoms of Infestation
As the larvae burrow into the tree, they create a series of tunnels that cause the tree’s stems and branches to become girdled. This effectively kills any live growth, causing the affected branches to wilt and die. The larvae also feed on vital nutrients that trees require to flourish. As the larvae feed, the tree gradually loses its nutrient supply, causing it to wither, and eventually expire.
- Trees should be thoroughly inspected for Asian long-horned beetle at least once a month during summer and early fall. This is when the Asian long-horned beetle is most active.
- If a tree is determined to have been infested by Asian long-horned beetle, it should be promptly removed in order to prevent the insect from spreading to other trees. Once the tree has been removed, the remaining woody materials should be properly disposed of.
Bagworm (Thyridopteryx ephemeraeformis),
Bagworm, also referred to as eastern bagworm, common bagworm, common basket worm, North American bagworm, or evergreen bagworm, is a native insect that infests many deciduous and evergreen tree species. The insect is named for the bag that it weaves during its larval stage. Bagworm is a voracious feeder, often defoliating the trees on which it resides. As such, it is considered a serious nuisance of host trees.
Bagworm infests a multitude of hosts. It prefers arbovitae and red cedar, but will also infest apple, birch, black locust, cypress, elm, honeylocust, Indian hawthorn, juniper, ligustrum, maple, oak, pine, poplar, spruce, sycamore, viburnum, and willow.
Symptoms of Infestation
Bagworm larvae feed on the upper foliage of host plants, often gnawing small holes in the leaves, or needles. On evergreen trees, the larvae’s feeding causes the branch tips to turn brown. Severe infestations often result in significant defoliation. The insect’s persistent feeding reduces tree vigor, and may culminate in tree mortality. Deciduous trees that are healthy, but have been defoliated will usually produce a second flush of foliage by the end of the growing season. Once the larvae mature, and begin fastening their bags to nearby branches, the silk that the larvae use to secure the bags can produce a girdling effect. If the silk remains fixed to the branch for several years, the branch may die back. As the larvae prepare to pupate, the bags can be observed attached to the branches of host trees.
- Bags from the previous year may be removed by hand in early spring, before the eggs begin to hatch.
- Bags may be pruned from infested plants during late fall, winter, or early spring. The bags become more conspicuous in fall once they have turned brown. Administer a pruning cut to the silken thread that holds them aloft, and safely dispose of the bags.
- Various insecticidal sprays can be utilized to control bagworm infestations. This method is ideal when bagworms become too numerous to control naturally. Applications should be performed in June, when the larvae are small. The larvae become more resistant to insecticidal sprays as they mature.
- Under certain weather conditions, entomopathogenic nematodes can help to reduce larvae populations.
- Bagworm has a plethora of natural predators that help to limit its populations. These predators comprise at least eleven species of parasitic wasps, including Pimpla disparis, Itoplectis conquisitor, and Gabrus ultimus. Other natural predators that commonly feed on the eggs and larvae include white-footed mice, and sparrows.
Photo courtesy of David J. Barber CC-by-3.0