Leucoma salicis

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1141029
Taxonomy
Kingdom: Animalia
Phylum: Arthropoda
Class: Hexapoda (including Insecta)
Order: Lepidoptera
Family: Lymantriidae
Genus: Leucoma
Species: salicis
Scientific Name
Leucoma salicis
(Linnaeus)
Scientific Name Synonym
Leucoma salica
(Linnaeus, 1758)
Common Names

white satin moth

Authors: Victoria Wilkin and Laura Timms, Faculty of Forestry, University of Toronto

Contents

Identification

The adults of the satin moth are silvery-white with a black body that is densely covered with white hairs, giving it mostly a white appearance with some dark showing through. Its wingspan is approx. 1 ½ to 2 inches (30 – 50mm) and its body length is approx. 15 to 20mm long. Male adult moths have antennae that are like feather tufts, while the females have antennae that are more thread-like.

The pupa of the satin moth is shiny black and covered in yellow, it is about 15 to 20mm long. The pupae are often found inside rolled leaves in a cocoon of white silk. At the larval stage they are pale to medium grey-brown with a darker head and back. Along the middle of the back there is a row of large circular, double patches that are shiny milk-white or yellowish. Beside these patches are two sub-dorsal broken yellowish lines, as well as two lateral and sub-dorsal rows of reddish-brown tufts. Finally, the eggs of Leucoma salicis are flattened and light green in colour, and are laid in one or two layers. The oval masses usually contain between 150 – 200 eggs that are covered in a white secretion.

Hosts

The satin moth was thought originally to only feed on exotic poplars, such as European white poplar (Populus alba L.) and Lombardy poplar (Populus nigra L. cv. italica). However more recently, the moth has begun to feed on other Populus spp. like trembling aspen (P. tremuloides), cottonwoods, and sometimes willow (Salix spp.). [1]

Geographic Distribution

Leucoma salicis is a native species to Europe and Asia. It was introduced to North America in the early 1900’s when it was first found in Boston, Massachusetts and British Columbia. [2] Today the Satin Moth is distributed much wider in North America, on the East it can be found from Newfoundland through to the North-eastern U.S. and into Quebec and Ontario. In the West it is found from British Columbia and parts of Alberta through to Northern California. [1]

Damage

After overwintering, the third instar larvae start to appear in late April, and feeding begins. The most damage is done to the tree in June when the third instars feed on the new leaves, devouring them completely. The first and second instars can also cause damage when they appear in late July through to September. These first and second instar larvae are skeletonizers and eat the entire leaf leaving only the petioles and veins.[2]

Though the satin moth was thought to generally be a defoliator of shade or park trees, it has been found to attack large, natural stands of “Poplar” spp. throughout Canada. During large infestations the leaves of the tree may turn brown and drop to the ground. [1]

The annual defoliation caused by the Satin Moth does not pose a problem for poplar trees as they regenerate within several weeks. However outbreaks in succession over a few years do pose a problem as they severely inhibit the trees ability to regenerate, causing lower growth and less tolerance to harsh climatic conditions. [3] These weakened trees may also become susceptible to infections, fungi, and other pests. Chen et. al [4] state that loss of foliage over 40% and the presence of 16 caterpillars per m3 of leaves cause dieback of trees to the point of death (based on calculated threshold). Intense outbreaks of Leucoma salicis have been found to cause foliage reduction of up to 80%. [3]

Life Cycle

Leucoma salicis has one generation annually. In July to late August females lay eggs on the leaves or sometimes bark of trees. Eggs hatch within about 2 weeks. The first and second instar larvae skeletonize the leaves until early September when they spin a silken web in bark crevices or under moss, in which they hibernate throughout the winter. The third instars emerge from hibernation in late April and feed on leaves, completely consuming them, until they pupate in mid-June. The larvae pupate in cocoons that are usually rolled up in leaves or bark crevices. The adults begin to emerge in early July usually about 10 days after pupation began. [1]

Population Dynamics

The outbreaks of the Satin Moth have been increasing in severity throughout North America and their impact is becoming much more economically important as they stray from ornamental trees to natural and planted stands. [5]

There is not very much known about their outbreak cycles; however there seems to be a correlation between the outbreaks and climatic conditions that favour insect development. It has also been noted that the outbreaks tend to follow previous outbreaks of forest tent caterpillar (Malacosoma disstria). A sudden decrease in population of the satin moth during an outbreak has been well documented and is caused by harsh winters of -20oC or below as well as native parasitoids and pathogens. [3]

Control and Management

In North America, Leucoma salicis has many natural enemies, such as birds, and predatory insects which attack the larvae. They have been found to be most easily controlled using parasitoids. [5] From 1929 to 1934 parasites were released in British Columbia in order to control populations of the satin moth. These included 3 wasps Apanteles melanoscelus, Eupteromalus nidulans, and Meteorus versicolor; and a fly Compsilura concinnata. It was found that A. melanocelus was the most effective in controlling the moth. [1]

There is no practical way of preventing Leucoma salicis from accessing a tree, but they can be controlled by the bio-insecticides containing the bacterial strain Bacillus thuringiensis var. kurstaki (Btk). This should be sprayed on the leaves of infected trees, where the larvae will ingest the bacterium and should stop feeding and die within 2 to 5 days of application. As the insecticide is most effective against the early instars of the Satin Moth, spraying should be done in the late summer to early fall, before hibernation. [5] Whenever choosing a pesticide to control a pest, consult your local extension office or department of agriculture for the most up to date and accurate recommendations for your area.

References

  1. Humphreys, N. 1996. Satin moth in British Columbia. Natural Resources Canada, Canada Forestry Service, Pacific Forestry Centre Victoria, BC. For. Pest Leaflet 38. [http://warehouse.pfc.forestry.ca/pfc/4610.pdf 1.0 1.1 1.2 1.3 1.4
  2. Natural Resources Canada. 2009. Insects and Diseases of Canada’s Forests, Satin Moth. http://imfc.cfl.scf.rncan.gc.ca/insecte-insect-eng.asp?geID=9504&ind=S 2.0 2.1
  3. Zeimnicka J. 2008. Outbreaks and Natural Viral Epizootics of the Satin Moth Leucoma salicis L. (Lepidoptera: Lymantriidae). Journal of Plant Protection Research vol. 48 no. 1 3.0 3.1 3.2
  4. Chen, Y. X. 1990. Studies on damage index of five foliar pests of poplars. Forest Pest and Disease 1: 17–20.
  5. Wyoming Pest Detection Program. 2004. Insect Alert – White Satin Moth (Leucoma salicis L.) http://uwadmnweb.uwyo.edu/capsweb/pest_alert/insect_alert_leucoma_salicis.pdf 5.0 5.1 5.2

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