DFTM Early Warning System: Background Information

Douglas-fir Tussock Moth
Early Warning System

Background Information

     Hosts, Effects & Outbreak Patterns
     Pheromone-Based Monitoring System
     Early Warning System Development
     Early Warning System Overview
     References

Hosts, Effects, and Outbreak Patterns

The Douglas-fir tussock moth Orgyia pseudotsugata (McDunnough) is a severe defoliator of Douglas-fir Pseudotsuga menziesii, var. glauca (Beissen.) Franco and true firs Abies spp. in the interior western United States and parts of the dry interior forests of southern British Columbia (Brookes et al., 1978). Douglas-fir tussock moth (DFTM) populations can increase rapidly, leading to outbreaks that occur with little or no warning. Defoliation may cause top-kill, loss of increment growth, direct tree mortality, and indirect mortality due to increased susceptibility of defoliated trees to bark beetle attack (Berryman & Wright, 1978).

In addition to the loss of timber, DFTM also causes increased risk of wildfire due to increased fuels and fuel ladders, increased stream runoff and other hydrologic impacts that could influence fish habitat, and changes in vegetation structure that could influence the quality of wildlife habitat (Klock & Wickman, 1978; Schreuder, 1978). DFTM larval hairs may also cause severe allergic responses for some people and domestic animals (Perlman et al., 1976). This can be a significant problem when high DFTM population densities occur near campgrounds, resorts, human habitations, or other forest sites frequented by the public.

Effective management actions to mitigate undesirable impacts of DFTM outbreaks are difficult to implement because of the abrupt nature of outbreak occurrence. Aerial surveys are helpful in detecting defoliation; however, in the case of DFTM, aerial detection usually occurs after the outbreak is in progress and substantial defoliation has already taken place. Tussock moth populations also have a strong tendency to aggregate (Shepherd et al., 1985; Mason, 1996), so that locating increasing populations on a landscape by using traditional ground-based sampling techniques requires intensive field work.

	Hosts, Effects & Outbreak Patterns			Early Warning System Overview
	Pheromone-Based Monitoring System			References
	Early Warning System Development

Pheromone-Based Monitoring System

When the sex attractant pheromone for DFTM was identified and synthesized in 1975 (Smith et al., 1975a; Smith et al., 1975b), its potential application in a pheromone-based trapping system for detecting and monitoring DFTM population changes was recognized. Beginning in 1979, standardized pheromone-baited traps were installed by federal and state cooperators in most western states with susceptible forest type as an early warning system for detecting areas with increasing DFTM populations. The objective of this system was to provide an early warning that would focus the attention of forest managers on areas where DFTM populations were likely to increase to outbreak levels within one or two years.

This pheromone-based approach for monitoring large areas of susceptible forest to forecast significant increases in populations may have application to other forest insects. Rapid changes in population density have been exhibed by other forest defoliators including nun moth Lymantria monacha and pine beauty moth Panolis flammea in Europe (Bejer, 1988; Watt & Leather, 1988), Siberian silk moth Dendrolimus sibericus and other Dendrolimus species in Asia (Gara, 1991), gypsy moth Lymantria dispar in eastern North America (Campbell & Sloan, 1978), and teak defoliator Hyblaea puera in India (Nair, 1988).

Several pheromone-based monitoring tools have been proposed or developed for forest defoliators. These have generally been designed for smaller spatial areas, such as for DFTM populations in British Columbia (Shepherd et al.,1985) or Nantucket pine tip moth Rhyacionia frustrana in loblolly pine plantations (Asaro & Berisford, 2001). Bogenschutz (1982) experimented with pheromone traps for monitoring nun moth populations, and Watt and Leather (1988) considered the merits of pheromone traps for monitoring pine beauty moth, but neither of these proposed tools has been widely tested. An effort of similar scale to the DFTM EWS is the application of pheromone-baited traps to monitor the spruce budworm, Choristoneura fumiferana, in Canada and in some of the New England States of the USA. Outbreak trends are determined by correlating trapped moth numbers with densities of immature stages of the insect (Sanders 1988; 1996). A basic difference from the DFTM system is the use of a higher strength lure with a high-volume trap (to avoid trap saturation).

	Hosts, Effects & Outbreak Patterns			Early Warning System Overview
	Pheromone-Based Monitoring System			References
	Early Warning System Development

Development of the Early Warning System

Early field tests and bioassays (Daterman et al., 1976; Livingston & Daterman, 1977) demonstrated the strong attraction of trap lures containing Z-6-heneicosen-11-one, the synthesized sex attractant of the Douglas-fir tussock moth (Smith et al., 1975a). Traps baited with the synthetic pheromone captured moths in geographic locations from which they had not previously been reported (Livingston & Daterman, 1977), and it was not uncommon for the traps to be filled to capacity with male moths. Because of the attractive potency of the pheromone, a range of low-strength pheromone releasers were tested as potential monitoring lures for detecting significant changes in population densities of the DFTM. Methods for developing the standardized lure formulation and trap design have been previously described by Daterman (1978) and Daterman et al. (1979).

The emphasis for development of the DFTM early warning system was on efficacy, low cost, and simplicity of trap design, placement, and maintenance. The trapping device is a modified �-gallon milk carton cut to a delta-shape with interiors lined with adhesive to entrap male moths. Standard lures are 3mm X 5mm polyvinyl chloride (PVC) pellets (Fitzgerald et al., 1973) containing 0.001% synthetic pheromone on a weight basis. Only the Z-6-heneicosen-11-one pheromone component has been used in this monitoring system. A second pheromone component, (Z)6,(E)8-heneicosadien-11-one, was recently identified (Gries et al.,1997), but this attraction enhancing compound was not needed for, and has not been used in, the DFTM early warning system.

Trap lure strength was calibrated to minimize moth captures in low-density population conditions, yet still signal when populations increase to pre-outbreak levels. The standard 0.001% PVC lure was chosen from a range of lure strengths and controlled-release formulations that were tested in the field by comparing moth captures in areas of known DFTM infestations representing very low to very high population densities (Daterman, 1978).

	Hosts, Effects & Outbreak Patterns			Early Warning System Overview
	Pheromone-Based Monitoring System			References
	Early Warning System Development

Early Warning System Overview

View 2 key references:
How to Use Pheromone Traps to Determine Outbreak Potential (Daterman and others 1979)
How to Identify Tussock Moths Caught in Pheromone Traps (Daterman and others 1977)

The early warning system was implemented in 1979 and 1980 in most western states with forests susceptible to DFTM. Although the number of plots has varied from year to year, approximately 800 plots are currently maintained annually, and distributed in forests of Arizona, California, Colorado, Idaho, Montana, Oregon, Utah, and Washington (table). Traps are placed near the ends of branches on relatively open-grown host trees. They are oriented perpendicular to the long axis of the branches, and attached about 2 to 2.5-meters above ground. Within each plot, five traps are placed at 25+ meter intervals (and 25+ meters away from roads) in stands with host trees. Local forest managers or forest health protection specialists decide where plots should be located, with most sites placed within areas having a recorded history of DFTM outbreaks. Traps are set out from late July to mid-August and picked up in mid-October to early November of each year. State and federal agencies, and in some cases private organizations, cooperate in conducting the annual trapping and share the resulting information.

Plots averaging 25 or more moths per trap signal DFTM populations potentially capable of causing visible defoliation within one to two years (Daterman et al., 1979). Once trap captures reach these threshold levels, ground sampling for larvae or egg masses in the general area of the plot becomes necessary to more precisely locate the infestation and evaluate its status. The density of plots covering an area and numbers of plots recording threshold capture numbers will influence when and where the ground sampling should be implemented (see later section).

Data regarding annual trap catches, plot locations, and annual defoliation records were provided by USDA Forest Service cooperators from the Intermountain, Northern, Pacific Northwest, Pacific Southwest, Rocky Mountain, and Southwestern Regions, other federal agencies (Bureau of Land Management, Bureau of Indian Affairs), and by state and private cooperators from California, Idaho, Montana, Oregon, and Washington.

	Hosts, Effects & Outbreak Patterns			Early Warning System Overview
	Pheromone-Based Monitoring System			References
	Early Warning System Development

References

Brookes, M.H., R.W. Stark, and R.W. Campbell (eds). 1978. The Douglas-fir tussock Moth: A Synthesis. USDA For. Serv. Tech. Bull. 1585. 331 p.

Campbell, S. and L. Liegel (tech. coords.), M.H Brookes (ed.). 1996. Disturbance and forest health in Oregon and Washington. USDA For. Serv. Gen. Tech. Rep. PNW-GTR-381.105 p.

Dahlsten, D.L., D.L. Rowney, W.A. Copper, and J.M. Wenz. 1992. Comparison of artificial pupation shelters and other monitoring methods for endemic populations of Douglas-Fir tussock moth, Orgyia psuedotsugata (McDunnough) (Lepidoptera: Lymantriidae). Can. Entomol. 124:359-369.

Daterman, G.E. 1980. Pheromone responses of forest Lepidoptera; implications for dispersal and pest management. P. 251-265 in Proc. of Second IUFRO Conference: Dispersal of forest insects: evaluation, theory and management implications, A.A. Berryman and L. Safranyik (eds.). Washington State Univ., Pullman.

Daterman, G.E., L.J. Peterson, R.G. Robbins, L.L. Sower, G.D. Daves, and R.G. Smith. 1976. Laboratory and field bioassay of the Douglas-fir tussock moth pheromone, Z-6-heneicosen-11-one. Environ. Entomol. 5:1187-1190.

Fettig, C.J., J. Fidgen, Q.C. McClellan, and S.M. Salom. 2001. Sampling methods for forest and shade tree insects of North America. USDA For. Serv. For. Health Techn. Enter. Team FHTET-2001-01. Morgantown, WV. 273 p.

Daterman, G.E., R.L. Livingston, J.M. Wenz, and L.L. Sower. 1979. How to use pheromone traps to determine outbreak potential. USDA For. Serv. Douglas-fir Tussock Moth Handb. No. 546. Washington, DC. 11 p.

Gries, G., et al. 1997. (Z)6, (E)8-heneicosadien-11-one: Synergistic sex pheromone component of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough) (Lepidoptera: Lymantriidae). J. Chem. Ecol., 23:19-34.

Hessburg, P.F., R.G. Mitchell, and. G.M. Filip. 1994. Historical and current roles of insects and pathogens in eastern Oregon and Washington forested landscapes. USDA For. Serv. Gen. Tech. Rep. PNW-GTR-327. 72 p.

Mason, R.R. 1979. How to sample Douglas-fir tussock moth larvae. USDA For. Serv. Douglas-fir Tussock Moth Handb. No. 547. Washington, DC. 15 p.

Mason, R.R. 1996. Dynamic behavior of Douglas-fir tussock moth populations in the Pacific Northwest. For. Sci. 42:182-191.

Mason. R.R., D.W. Scott, and H.G. Paul. 1993. Forecasting outbreaks of the Douglas-Fir tussock moth from lower crown cocoon samples. USDA For. Serv. Res. Pap. PNW-RP-460.12 p.

Mason, R.R., D.W. Scott, M.D. Loewen, and H.G. Paul. 1998. Recurrent outbreak of the Douglas-fir tussock moth in the Malheur National Forest: A case history. USDA For. Serv. Gen. Tech. Rep. PNW-GTR-402. 14 p.

Randall, C. 2001. Douglas-fir tussock moth biological evaluation, Palouse Ranger District, Clearwater National Forest - 2000. USDA For. Serv. Rep. 01-4. Missoula, MT. 30 p.

Shepherd, R.F. and I.S. Otvos. 1986. Pest management of Douglas-fir tussock moth: procedures for insect monitoring, problem evaluation, and control actions. Can. For. Serv. Pacific Forest Centre Info. Rep. BC-X-270. Victoria, BC. 14 p.

Shepherd, R.F., D.D. Bennett, J.W. Dale, S. Tunnock, R.E. Dolph, and R.W. Thier. 1988. Evidence of synchronized cycles in outbreak patterns of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough) (Lepidoptera: Lymantriidae). Mem. Entomol. Soc. Can. 146:107-121.

Shepherd, R.F., I.S. Otvos, and R.J. Chorney. 1984. Pest management of Douglas-fir tussock moth (Lepidoptera: Lymantriidae): a sequential sampling method to determine egg mass density. Can. Entomol. 116:1041-1049.

Shepherd, R.F., T.G. Gray, R.J. Chorney, and G.E. Daterman. 1985. Pest management of Douglas-fir tussock moth, Orgyia pseudotsugata (Lepidoptera: Lymantriidae): monitoring endemic populations with pheromone traps to detect incipient outbreaks. Can. Entomol. 117:839-848.

Smith, R.G., G.E. Daterman, and G.D. Daves, Jr. 1975. Douglas-fir tussock moth: sex pheromone identification and synthesis. Science 188:63-64.

Sower, L.L., J.M. Wenz, D.L. Dahlsten, and G.E. Daterman. 1990. Field testing of pheromone disruption on preoutbreak populations of Douglas-fir tussock moth (Lepidoptera: Lymantriidae). J. Econ. Entomol. 83:1487-1491.

Wickman, B.E. 1992. Forest health in the Blue Mountains: the influence of insects and diseases. USDA For. Serv. Gen. Tech. Rep. PNW-GTR-295.