"Fostering education on the pests of California forests since 1951."
Many different species of defoliators currently threaten California forests. Some native, some not, defoliators are adult and larval insects that strip all the leaves or needles from a tree or shrub. Defoliation interferes with plant photosynthesis causing intesnse damage and or death.
Defoliators
California Oakworm
Phryganidia californica
Location: California
Impact Significance: California oakworm is the most important oak-feeding caterpillar throughout its range. Populations vary unpredictably year to year from very high to undetectably low.
Hosts: California live oak and California white oak, but they will feed on all oaks and have been reported to feed on American chestnut, eucalyptus, azaleas and tanoak.
Biology: California oakworm normally has two generations per year, a 3-month summer brood and a 9-month winter brood. Young larvae feed on soft tissue of leaf veins and older larvae chew from the edge of the leaf inward to the midrib. The larvae pupate on the lower trunks of oak trees and moths may appear almost any time from March through November. Oak moths may be seen during summer fluttering around oaks in the late afternoon.
Damage: During epidemics, every green part of the foliage is eaten. Partially chewed leaves may turn brown and die. Trees under stress from drought or other factors may decline if defoliated, whereas healthy trees can tolerate oakworm damage.
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Douglas Fir Tussock Moth
Orgyia pseudotsugata
Location: California, British Columbia, Idaho, Washington, Oregon, Nevada, Arizona and New Mexico.
Impact Significance: A defoliator that during severe outbreaks cause severe defoliation. Trees can appear skeletons and damage from the severe defoliation can lead to tree death or predispose trees to subsequent bark beetle attack. It is one of the most damaging of the western defoliators.
Hosts: Douglas-fir, true firs and spruce.
Biology: Douglas-fir tussock moth has 1 year life cycle and overwinters as eggs. Egg hatch coincides with bud burst where the larvae feed on the current years foliage. Pupation occurs any time from late July to the end of August inside a thin cocoon of silken webbing mixed with larval hairs. Adults will appear from late July to November, depending on location and the female moth emits a pheromone that attracts males.
Damage: During epidemics, every green part of the foliage is eaten. Partially chewed leaves may turn brown and die. Trees under stress from drought or other factors may decline if defoliated, whereas healthy trees can tolerate oakworm damage.
Douglas fir tussock moth
Douglas Fir Tussock Moth
Douglas fir tussock moth
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Gypsy Moth
Lymantria dispar
The gypsy moth (GM) is a pest that voraciously feeds on the leaves of trees and shrubs, threatening residential settings, forests and agricultural tree crops.
Location: Europe, US, California
Impact Significance: Gypsy moth caterpillars feed on hundreds of kinds of plants and are capable of defoliating trees at an alarming rate. A single gypsy moth caterpillar can eat up to one square foot of leaves per day. In the northeastern United States, millions of these caterpillars emerge each spring and devour large swaths of forest and foliage.
Hosts: Young caterpillars feed primarily on oaks, aspen, birch, willows and alder, and older caterpillars feed on a broader range of trees including cedar, pine, spruce and fir. Common California species such as manzanita, western hemlock, Douglas fir and live oak are also prone to damage by this pest.
Biology: The strain of gypsy moth established in the U.S. is commonly called the European gypsy moth (EGM). This is to distinguish it from a strain that exists in Asia, called the Asian gypsy moth (AGM).
Damage: When trees are repeatedly defoliated, they are rendered more susceptible to other pests and diseases, potentially leading to tree death and an increased potential for fire and erosion.
Gypsy moth
Gypsy moth larvae
Gypsy moth
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Fruit Tree Leafroller
Archips argyrospila
Location: Most of United States and southern Canada
Impact Significance: Fruittree leafroller rarely have populations heavy enough to cause a reduction in the crop, but can have unsightly scars on the fruit that increases in size as the fruit enlarges.
Hosts: Oak, hawthorn, white birch, elm, maple, hickory, black and persian walnut, California buckeye, popular, cherry, pear and rose. Common pest of apple and crapapple.
Biology: Fruittree leafrolller has one generation per year. Adult moths are about 0.5 inches long and rusty brown wings marked with areas of white and gold. When at rest the adults show the typical bell-shaped pattern common to the family Tortricidae. They overwinter in eggs are laid in masses on limbs and twigs, and covered with a gray secretion that turns white upon aging. The larvae are green with a black head and they feed within opening buds. When they mature they tie the leaves together and feed on the leaves, blossoms and small fruit. Adults emerge in May or June.
Fruit tree leafroller
Fruit tree leafroller
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Pandora Moth
Coloradia pandora
Location: Western United States
Impact Significance: During outbreaks, growth loss and mortality can be significant.
Hosts: Lodgepole, Jeffrey and ponderosa pines. Occasionally sugar, coulter an pinyon pines.
Biology: The pandora moth requires 2 years to complete its life cycle. The first winter is spent as larvae in the tree canopy and the second is spent as pupae in the litter or soil. Moths emerge from the buried pupal cases, mate, and lay an average or 80 eggs on the bark and needles of pines. Young larvae feed on the needles of terminal shoots on the outer branches. Larvae overwinter at the base of needles in strands of silk and when warmer weather returns, feeding resumes. At this stage needles of all age classes are consumed, but the buds are not damaged. When fully grown larvae crawl down the tree trunks into the soil, preferring pumice or decomposed granite, to pupate.
Damage: During epidemics, every green part of the foliage is eaten. Partially chewed leaves may turn brown and die. Trees under stress from drought or other factors may decline if defoliated, whereas healthy trees can tolerate oakworm damage.
Pandora moth
Pandora moth larvae
Pandora moth
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Ponderosa Pine Tip Moth
Rhyacionia zozana
Location: California, Oregon and Washington
Impact Significance: Larval damage to the central growing terminal can significantly alter the trees shape, causing regrowth of stems to be bunchy, crooked or forked.
Hosts: Ponderosa and Jeffrey pines.
Biology: The female lays eggs singly on the new growth tips. The larvae feed inside the needle sheaths or buds and then enter new shoots and mine within developing shoots. Once larval growth is complete by midsummer of fall, they emerge from the shoots and drop to the ground to pupate and overwinter.
Damage: Infested trees are often deformed and growth is reduced. Damage is unsightly but seldom fatal.
Ponderosa pine tip moth
Ponderosa pine tip moth damage
Ponderosa pine tip moth
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Stevens, R. 1966. The ponderosa pine tip moth, Rhyacionia zozana, in California (Lepidoptera: Olethreutidae). Annals of the Entomological Society of America, 59:186-192.
Silver Spotted Tiger Moth
Lophocampa argentata
More information coming soon
Silver spotted tiger moth
Silver spotted tiger moth larvae
Silver spotted tiger moth
Spotted Lanternfly
Lycorma delicatula
More information coming soon
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Spotted lanternfly
Spotted lanternfly
Spotted lanternfly
Western Spruce Budworm
Choristoneura freeman
More information coming soon
Western spruce budworm
Western Spruce Budworm
Western spruce budworm