Spongy Moth

Spongy Moth Spread in North America

Research Issue

The spongy moth (SM), Lymantria dispar (L.), is a voracious defoliator accidentally introduced at Medford, Massachusetts, in 1869. Its larvae eat leaves from many deciduous tree species, often totally defoliating them, but it prefers oaks (although later-stage larvae can eat conifer needles if necessary to survive). The SM has spread over 860,000 km2 in North America, just one-fourth of the range of susceptible hosts. The “invasion front”— the naturally moving edge of the SM infestation— historically (1960-1988) moved about 20 km annually prior to the implementation of the Gypsy Moth Slow the Spread program. This program has reduced SM spread by more than half. Adult females of the European strain of the SM established in the U.S. are incapable of flight. Spongy moth larvae can crawl only about 100 feet before they pupate, but they can also move by windborne dispersal of young larvae “ballooning” on silken threads. However, egg masses are accidentally transported by humans, often for long distances, on firewood or outdoor recreational equipment. This transportation by humans has resulted in many isolated populations— some just ahead of the front and others far away, such as those in the Pacific Northwest and California that have been the target of intensive eradication efforts.

Our Research

The Northern Research Station (NRS) maintains research programs and data collection studying the various problems still associated with quantifying and understanding the invasion spread of SM. The NRS, because of its historical closeness to the initial introduction, has been studying the SM from the early parts of the 20th century. Recently, the 60 to70 years’ worth of data it maintains and the records from management activities are being used to study not just the pest itself but also the dynamics and ecology of the invasion process. 

Expected Outcomes

Development of a better understanding of the population processes operating during SM spread provides information critical for the development of more effective approaches to both slowing the spread of SM and for eradicating isolated populations in un-infested states.  This work is also of broader significance and provides an excellent model system for understanding the establishment and spread of invading species in general.

Research Results

This research focuses on both the population processes operating along the continuously infested population front, and the establishment and spread of isolated populations in un-infested areas such as the Pacific Coast states. Results indicate that when the SM first establishes in an area, they exist at very low densities and they are strongly affected by an “Allee effect” — the phenomenon of decreasing population growth with decreasing density. In the case of invading SM populations, the Allee effect arises primarily by the inability of males and females to locate each other for mating at low-densities. Despite the fact that the SM possesses a highly evolved system for mate location, a large fraction of females go unmated at very low densities. The importance of mate-location failure in the establishment of SM populations provides opportunities for the use of mating disruption and other intervention tactics to eradicate isolated populations or slow the spread of populations along the advancing population front.

Tobin, P.C.; Onufrieva, K.S.; Thorpe, K.W. 2013. The relationship between male moth density and female mating success in invading populations of Lymantria dispar (L.). Entomologia Experimentalis et Applicata 146: 103-11.

Tobin, P.C.; Robinet, C.; Johnson, D.M.; Whitmire, S.L.; Bjørnstad, O.N.; Liebhold, A. M. 2009. The role of Allee effects in gypsy moth (Lymantria dispar (L.)) invasions. Population Ecology 51: 373-384.

Robinet, C.; Lance, D.R.; Thorpe, K.W.;  Tcheslavskaia, K.S.; Tobin, P.C.; Liebhold, A.M. 2008. Dispersion in time and space affect mating success and Allee effects in invading gypsy moth populations. Journal of Animal Ecology 77: 966-973.

Tobin, P.C.; Whitmire, S.L.; Johnson, D.M.; Bjørnstad, O.N.; Liebhold, A.M. 2007. Invasion speed is affected by geographic variation in the strength of Allee effects. Ecology Letters 10: 36-43.

Liebhold, A.M.; Tobin, P.C. 2006. Growth of newly established alien populations: Comparison of North American gypsy moth colonies with invasion theory. Population Ecology 48: 253-262.

Johnson, D.M.; Liebhold, A.M.; Tobin, P.C.; Bjørnstad, O.N. 2006. Allee effects and pulsed invasion by the gypsy moth. Nature 444: 361-363.

Research Participants

Principal Investigators

  • Patrick Tobin, University of Washington, School of Environmental and Forest Sciences
  • Andrew Liebhold, USDA Forest Service Northern Research Station Research


Last Modified: March 4, 2022