Alternative Treatments for Gypsy Moth in B.C.

Several alternatives to spraying with Btk can help reduce gypsy moth populations. Most are less effective than Btk application and therefore unsuitable for eradication programs. They can be helpful under certain circumstances, however — particularly for treating very small, isolated populations. They include:

Most Common Alternative

No Treatment

If pheromone-trapping results determine that a population is small and isolated, treatment might be delayed. The decision to delay treatment is site-specific and can be due to many factors, such as:

  • Initial trapping density
  • Host availability
  • Climate suitability 
  • Location of the infestation

Usually, populations detected in B.C. are small and isolated and are left untreated. Typically they fail to establish and then die out on their own.

Trap density can be intensified to monitor for an increase in population size and to define an area of infestation. A decision to treat further will depend on the results of this more intensive trapping schedule. When evidence shows a small and isolated population is growing, treatments probably will proceed.

Occasionally Used Alternatives

Host Removal

If the source of a gypsy moth population is known and is isolated, the population sometimes can be eradicated by removing and destroying the host vegetation.


A small population of gypsy moths was eradicated in a New Westminster schoolyard in 1997 by removing infested brush and other vegetation.


It is rarely possible to pinpoint the sources of male moths caught in pheromone traps. These traps are effective at attracting moths over several hundred metres, thus providing only the general location of the population.

If the source of the moths cannot be isolated to a specific, small area, removing all vegetation would be

  • very costly,
  • unacceptable to the public, and
  • ineffective.

Egg-Mass Removal

Egg-mass removal is a non-chemical, manual treatment that will, in theory, eradicate the gypsy moth. Egg masses should be removed from the late fall through early spring, before eggs hatch.

Egg-mass searches are used in B.C. to help justify treatment of a population identified by delimiting trapping. Any egg mass found during these searches is removed and destroyed.

Egg-mass removal has never been considered or proved to be an effective eradication method on its own.


Egg-mass removal was done in Courtenay (1983), Chilliwack (1985), Parksville (1989), Richmond (1992), Saanich (1991) South Vancouver (1993) and Saltspring Island (2006). It did not eradicate any of these populations.


Females will deposit their eggs on nearly any stationery object. They tend to select sheltered areas such as crevices or under fence rails. They will also lay their eggs high in the canopy of trees. Eggs, therefore, can be very difficult to find and access. Roughly half of all egg masses laid cannot be reached from the ground. Many are on private properties, which often cannot be accessed.

Mass Trapping

Trapping is commonly used to monitor for gypsy moths. But mass trapping can be used as a treatment. If enough pheromone traps are placed in an infested area, any male moth in theory could be trapped before it has mated with a female. Trap densities are far higher in mas trapping than in delimiting trapping. For example, there would be one trap in every front yard and one in every back yard of every city lot within an urban trapping grid.

Though some questions remain about the effectiveness of mass trapping as an eradication method in B.C., the method does provide very accurate boundaries of an infested area, making it possible to reduce the treatment area if subsequent spraying is required.


Mass trapping was used in several locations over several years: Fairfield (1999), Sechelt (2000 & 2001), N. Delta (2002, 2003), Saanich (2003, 2005, 2006, 2007) and Abbotsford (2004), Gabriola Island (2004 and 2005), S. Duncan (2004 and 2005), Sidney (2007), Saltair (2008), Saltspring Island (2008) and Lake Cowichan (2008), with mixed results.

The Sidney, Gabriola and S. Duncan trials are considered successful examples of mass trapping, where the moth populations were eliminated over two years of treatment.

The 2008 Saltspring Island and Saltair treatments were preceded by a ground spray while the 2008 Lake Cowichan population appeared to go extinct on its own.

Testing of mass trapping will continue whenever possible to improve our understanding of the most effective conditions for its use.


Several aspects of mass trapping make it inferior to Btk spraying, particularly if a population is concentrated and growing.

  1. Does not necessarily prevent mating: Mass trapping is most likely to prevent mating in areas with a low density of gypsy moths, where males are less likely to have mated before they were trapped. 
  2. Requires a lot of resources: The high density of traps makes this an expensive, labour-intensive treatment.
  3. Not a proven eradication method: Mass-trapping trials have produced mixed to inconclusive results. It seems most likely to work on small, low-density populations.
  4. Takes a long time: Like any other method, mass-trapping requires at least two years of successive pheromone trapping periods with no moths caught to be declared a successful treatment. But, best practice is to conduct two years of mass trapping to treat an area, versus one year for spray treatments. This means that mass trapping takes at least one year longer than spray treatments

Possible Alternative Being Researched

Mating Disruption

If male moths are confused by multiple sources of synthetic female pheromone, they may fail to find a female gypsy moth to mate with. Tiny plastic flakes or plastic beads containing synthetic gypsy moth pheromone (Disparlure) are mixed in a sticky molasses-based carrier and released by aircraft over forested areas.

Mating disruption is being used with some success in the eastern United States, at the boundaries of areas with established gypsy moths. Mating-disruption products are not registered for use in Canada. The B.C. Government is monitoring research on mating disruption, and considering its potential as an eradication tool.