Lymantria moth treatments

In B.C., the Lymantria Moth Technical Advisory Committee of the B.C. Plant Protection Advisory Committee (BCPPAC) evaluates Lymantria moth management options and makes treatment recommendations. This Lymantria Moth Technical Committee is made up of federal and provincial government experts in Lymantria moth management.

When moths are detected in an area, the Lymantria Moth Technical Advisory Committee must decide whether that area will be treated and, if so, which treatment method to use. The Committee’s decision is based on many factors, such as:

  • The safety of the treatment to humans, non-target organisms and the environment
  • The number of moths caught in the area
  • The location and number of egg masses or other Lymantria moth life stages
  • The history of the infestation
  • The terrain and access to the area
  • The cost of the treatment
  • The likelihood of completely controlling the moths in the shortest time
  • The location and number of host trees
  • Other factors constraining the control method being considered

Treatment options

The most common and most effective treatment is spraying with Btk

In rare circumstances, mass trapping can be used.

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 mass 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.

Examples

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.

Disadvantages

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 Lymantria 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