Orgyia pseudotsugata
Encyclopedia
The Douglas-fir Tussock Moth (Orgyia pseudotsugata) is a moth
of the Lymantriidae
family. It is found in western North America
. Its population periodically irrupts in cyclical outbreaks
. The caterpillars feed on the needles of douglas-fir, true fir, and spruce in summer and moths are on the wing from July or August to November.
, Idaho
, Washington (state), Oregon
, Nevada
, California
, Arizona
, and New Mexico
. Outbreaks occur in cycles of about eight to twelve years and usually last up to four years, sometimes longer. Reports from Idaho and Washington state indicate 2011 has seen a major outbreak. The larvae feed on Pseudotsuga and Abies species, especially Douglas-fir, grand fir, white fir, and subalpine fir.
. They produce long silky threads which can catch the wind when they drop from one branch to another. They produce loose webbing which forms a netting. In this cocoon they pupate in July or August. Adults emerge and are active as late as November. The flightless females stay near the cocoons from which they emerged and mate straight away. Eggs are spherical and white and are laid in a mass which protects them through winter. Because the female is sedentary, population outbreaks always form in place.
-baited traps. Outbreaks subside on their own, but silvicultural techniques for managing affected timber can be employed, or the chemical Carbaryl
can be sprayed aerially.
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
of the Lymantriidae
Lymantriidae
Lymantriidae is a family of moths. Many of its component species are referred to as "Tussock moths" of one sort or another. The caterpillar, or larval, stage of these species often has a distinctive appearance of alternating bristles and haired projections...
family. It is found in western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Its population periodically irrupts in cyclical outbreaks
Population cycle
A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological...
. The caterpillars feed on the needles of douglas-fir, true fir, and spruce in summer and moths are on the wing from July or August to November.
Description
Adult males are grayish brown moths with mottled light and dark markings. The males' wingspread is 25–34 mm (0.984251968503937–1.3 in). When the wings are spread open the brown hindwings can be seen. Individuals in the northern part of its range are darker in color and southern population is lighter. Antennae are plumose (feathery). Females are flightless with only rudimentary wings. Larvae (caterpillars) are 20–26 mm (0.78740157480315–1 in) and colorful with red spots, white spines, conspicuous red-tipped white tufts or “tussocks“, and dense bunches of long, black hairs projecting to the front and behind.Range and host plants
The Douglas-fir Tussock Moth is native to forests of western North America and outbreaks have been identified in British ColumbiaBritish Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, Washington (state), Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, and New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. Outbreaks occur in cycles of about eight to twelve years and usually last up to four years, sometimes longer. Reports from Idaho and Washington state indicate 2011 has seen a major outbreak. The larvae feed on Pseudotsuga and Abies species, especially Douglas-fir, grand fir, white fir, and subalpine fir.
Life cycle
Eggs hatch in spring (May to June) and the young larvae begin feeding on new foliage (the current season’s growth of needles). Later, they feed on both new and old foliage. The movement of the caterpillars is the main means of biological dispersalBiological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
. They produce long silky threads which can catch the wind when they drop from one branch to another. They produce loose webbing which forms a netting. In this cocoon they pupate in July or August. Adults emerge and are active as late as November. The flightless females stay near the cocoons from which they emerged and mate straight away. Eggs are spherical and white and are laid in a mass which protects them through winter. Because the female is sedentary, population outbreaks always form in place.
Management
One key to management of outbreaks is detection. Entomologists monitor forests using an “early warning system” of pheromonePheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
-baited traps. Outbreaks subside on their own, but silvicultural techniques for managing affected timber can be employed, or the chemical Carbaryl
Carbaryl
Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid commonly sold under the brand name Sevin, a trademark of the Bayer Company. Union Carbide discovered carbaryl and introduced it commercially in 1958...
can be sprayed aerially.
Subspecies
- Orgyia pseudotsugata pseudotsugata (British Columbia to Idaho, western Montana, eastern Washington, Oregon, Colorado, Nevada, California)
- Orgyia pseudotsugata morosa Ferguson, 1978 (British Columbia to California)
- Orgyia pseudotsugata benigna Ferguson, 1978 (Arizona)