Douglas-fir Tussock Moth

Douglas-fir Tussock Moth - Not to be confused with the "miller" moths common in Cheyenne in late-spring and early-fall.  The male Douglas-fir tussock moth is similar in appearance to a miller moth, but it has feathery antennae and is in the flying adult stage in early-August to early-September.  The larvae or caterpillar of the Douglas-fir tussock moth feeds primarily on spruce trees in this area.   

                                      
Douglas-fir tussock moth damage seen on the spruce tree in the photo.  Typically the larvae feed on the needles (leaves) starting at the top of the tree and working down.  The larvae feed on younger needles first and then older needles as the larvae mature.  An affected spruce tree appears brown with sparse foliage.     Photo: Cheyenne Urban Forestry

Male Douglas-fir Tussock moth with feathery antenna.
Photo: Jerald E. Dewey, USDA Forest Service

Douglas-fir Tussock moth larva or caterpillar stage.
Photo: A. Steven Munson, USDA Forest Serv.
from: Forestry Images

The eggs are frequently laid on the pupal case and mixed with the gray hairs from the female moth and her pupal case.  The moth overwinters in the egg stage.  The eggs hatch in late-May to early-June in this area.  The caterpillars are very hairy throughout the various moults during the early summer months.  The young caterpillars feed on the new emerging spruce needles.  As the caterpillars mature they will feed on older needles.  Typical needle damage occurs in the tree canopy from the top of the tree down and from the outside of the limbs to the inside.  Severe and repeated damage to new needle growth can cause limb death and tree death.

Wingless female Douglas-fir tussock moth on pupal case.
Photo: Jerald E. Dewey USDA Forest 
Forestry Images

Douglas-fir Tussock moth larvae right center of photo, and left just above center, a pupal case from 2004, with a 2005 hatched egg mass on the pupal case.  Picture taken on July 28, 2005, on a single infested spruce tree in Brimmer Park.
Photo: Cheyenne Urban Forestry

Trees under stress are the primary targets of Douglas-fir tussock moth caterpillars.  We had three years, increasing in severity, of drought conditions prior to the 2002 heavy infestation of Douglas-fir tussock moth in the cemeteries.  The summer of 2002 was the second driest on record since 1895.  In addition to drought conditions, warmer temperature in winter allows more insects to survive. The best way to decrease Douglas-fir tussock moth infestations and subsequent damage is to keep the spruce trees healthy by providing plenty of water, including during the winter.  Douglas-fir Tussock moth can have cyclic outbreaks, which means the population increases over a few years and then crashes, and slowly builds up in size again, over nearly the same period of time, or they can have eruptive outbreaks meaning sporadic periods of higher populations.

Dendrex®, a brand name insecticide that contains Acephate, is labeled for systemic application for controlling Douglas-fir tussock moth larvae.  Dendrex was used in a trunk injection method in early June 2002.  The dry year of 2002 probably contributed greatly to the slow uptake and distribution of the systemic insecticide in the treated spruce trees.  Talstar® insecticide was used in early July 2002 to spray infested spruce trees in the Cheyenne cemeteries with a surprisingly high level of success.  No male Douglas-fir tussock moths were caught in any of the 60 pheromone traps in the cemeteries in late summer of 2002.

Additional information at: Colorado State University

Links:

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.