Non-spray Treatment Option for Gypsy Moth Eradication in British Columbia

Egg Mass Removal

In theory, removing all of the egg masses from an infested area will eradicate the gypsy moth. Egg mass removal is a non-chemical, manual treatment. It would be done from the late fall through to the early spring before eggs hatch. All egg masses found would be carefully removed to avoid spilling any eggs and then the egg mass would be destroyed.

A major disadvantage of this treatment stems from the egg laying habit of female gypsy moth. Females will deposit their eggs on nearly any stationery object and tend to select sheltered areas (e.g., crevices, under fence rails, etc.). They also will lay their eggs high in the canopy of trees making searching extremely difficult to complete adequately. Roughly half of all egg masses laid can not be reached from the ground. The egg mass searchers are also limited by their access onto private property by fences, gates, dogs, and by the sheer size of the area that requires searching. Completeness is also compromised if permission to search is not received from the property owner. Egg mass removal has never been considered or proven to be an effective eradication method on its own. Local examples where egg mass removal did not achieve eradication are from Courtney (1983), Chilliwack (1985), Parksville (1989), Richmond (1992), Saanich (1991)  South Vancouver (1993) and Saltspring Island (2006).  

Egg mass searches are conducted in B.C. to confirm the presence of a second life stage to further justify the treatment of a population identified by delimiting trapping.  Any egg mass found is removed and destroyed.  

Mass-trapping

Mass-trapping as a treatment for gypsy moth is based on the premise that if enough pheromone traps are placed in an infested area, any male moth will be trapped before it has successfully mated with a female. Trapping densities range from 1,920 to 5,760 traps/ square mile or 64 to 99 traps/acre - far higher than those used in delimiting trapping (= a trapping tactic used to delineate the location of an infestation, usually at 32 traps/acre). This equates roughly to placing one trap in every front yard and one in every back yard of every city lot within the trapping grid.  Each trap requires two visits - placement and trap removal.

The success of a mass-trapping treatment is monitored by comparing the number of male moths caught each year in the trapping grid and, if done thoroughly, the number and proportion of unfertilized egg masses found in the treatment area to the number and proportion of viable egg masses.  As noted above, egg masses are very difficult to find and may not be the best indicator of success.  If used for eradication, success is achieved when no moths are caught in the treatment area for two years after the treatment has been completed.

The BC Ministry of Forests and Range, in an effort to find alternatives to spraying, has employed mass trapping in several locations since 1999 in candidate locations, that is, at sites where populations were small, widely dispersed, and isolated from other populations.  Trials were conducted in Fairfield (1999), Sechelt (2000 & 2001), N. Delta (2002, 2003), Saanich (2003, 2005, 2006, 2007) and Abbotsford (2004), Gabriola Island (2004 and 2005) and in S. Duncan (2004 and 2005) and Sidney (2007) with mixed results (see trapping history page).  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.   At this time, mass trapping is still being tested in several locations to determine if and where it is effective.

The key advantages of mass trapping are

1. No spraying is required; and
2. Trapping results, even if fertile egg masses or populations fail to decline, provide highly accurate delimitation of moth populations resulting in a reduction in potential treatment areas (if required). 

Several aspects of mass-trapping that make it a less desirable alternative treatment to Btk spraying for eradicating a gypsy moth population, particularly one that is concentrated and growing:

1. Prevention of mating - To be a successful treatment, all male moths must be caught before they reach a female. Trapping does not guarantee that the male has not mated before it was caught. Effectiveness is likely improved if the treatment is done in areas where a small population of gypsy moths are widely dispersed but isolated from other populations. This distribution would increase the likelihood that a male would encounter a trap before a female gypsy moth. 
2. Resources - As noted above, the density of trapping required is extremely high (9 traps/acre) and will require a large commitment of manpower and resources. Rural areas that are not as densely roaded as urban areas would take much more time to hang and collect traps.
3. Not a proven eradication method - Mass-trapping trials have produced mixed to inconclusive results.  For example, a test done in Oregon in 1985 on a small population that was similar to those encountered in B.C. failed.  Previous trials in B.C. resulted in failure (i.e., viable egg masses and/or expanding populations resulting in a spray) or the results were inconclusive (i.e., populations may have died out on their own) (e.g., Fairfield (Victoria) and Abbotsford in 2000).  Over time, the MFR's experience with the mass trapping technique has produced criteria for identifying where its application may be suitable.  Past failures were likely due to applying the treatment in less than ideal conditions (i.e., where infestations were either large and concentrated) as was the case in the 1998 mass-trapping in Greater Victoria's Western Communities.    
4. Time to determine success - Mass-trapping requires at least two years of successive pheromone trapping periods with no moths caught to be be declared a successful treatment  - like any other treatment. Interim indicators of success are the discovery of unfertilized egg masses.  However, it is expected that it will take two years of mass trapping before the first year without positive trap catches whereas spray treatments usually only take one year of treatment.  In other words, it takes one year longer to conclude if a population has been successfully eradicated using mass trapping. 

If the conditions for deployment are determined and the effectiveness of the treatment is favourable, mass trapping could potentially replace spraying of small, isolated, and diffuse gypsy moth populations.

Mating Disruption

Like mass trapping, if male moths are confused by multiple sources of synthetic female pheromone they may fail to find a female gypsy moth thus preventing successful mating.  In the U.S., areas on the leading edge of the expanding range of gypsy moth are being treated to "slow the spread" using a technique called mating disruption (see http://www.gmsts.org/operations/).  Tiny plastic flakes or plastic beads containing synthetic gypsy moth pheromone (Disparlure) and mixed in a sticky molasses based carrier, are dispensed by aircraft over forested areas.  Success has been reported in achieving spread reduction targets using this method.  Mating disruption products are registered in the U.S. but are not registered in Canada and thus are not available for operational use.  The MFR is currently reviewing information on this technique as a potential eradication tool.  

Tree Banding

Tree-banding using burlap strips or sticky bands on the trunk of trees is a method that is used in areas where the gypsy moth are permanently established to monitor larval populations and provide some protection to trees from defoliation. Some gypsy moth caterpillars move down the tree trunks at daybreak to search for shelter from predators and then return to the tree crowns at night fall. The bands intercept these migrating larvae who are then collected daily or are caught and killed in the sticky band. The advantage of this treatment is that it does not require insecticide. However, there are several disadvantages that make it completely unsuitable for eradication and it is not a recommended treatment for use in B.C.

Band or strip placement is extremely labour intensive - thousands of trees would have to be treated for this method to be effective. Furthermore, the bands need to be visited every day to collect and kill any larvae that are hiding under them. If they are not removed, they will crawl out at night and may not be caught again.

The 1998 banding trial in the Western Communities caught one suspect caterpillar and one pupal case.  It did show that the behaviour of gypsy moth on large Garry oak is different than on smaller trees. Caterpillars generally stay in the tree crown (where there are ample hiding places) rather than migrating to the ground or the lower trunk where the bands or strips would be placed. Thus, this treatment is not effective.

Biological Controls

Classic biological control is achieved by the successful introduction and reproduction of predators, parasites or diseases that are specific to the pest organism. Biological control is used for pests that are exotic but established. For the B.C. gypsy moth situation, biological control will only work if there is a continuing, established gypsy moth population - a situation we are attempting to avoid by following the eradication strategy.  

Along with dispersal mortality and starvation, native natural enemies such as birds, spiders, and ants cause significant mortality to gypsy moth larvae in B.C. resulting in extinction of small populations.  However, gypsy moth reproduce rapidly under good growing conditions and populations can survive and grow despite this mortality.  Such growing conditions are found primarily in southern B.C.

An example of an ongoing long-term biological control project in B.C. is being performed by the Ministry of Forests and Range's Invasive Plant Program in Kamloops, B.C. A matrix of biological controls for various noxious weeds has been produced.

Introduction of new organisms is a long-term activity that requires careful screening to ensure that the biological control does not harm non-target native species. Since the gypsy moth is not established in B.C. or western North America, biological control is not a viable treatment option. Biological controls, particularly through the introduction of a fungus specific to gypsy moth called Entomophaga maimaiga, have been carried out in the established areas in eastern North America with some success. Current populations are suppressed by a combination of cold winters and high fungal mortality. Many other organisms have been introduced as potential biological control agents for gypsy moth in eastern North America with little, if any, effect.

A virus specific to gypsy moth has been successfully applied experimentally as an aerial insecticide to control populations in eastern North America. The virus is reproduced by rearing gypsy moth larvae, infecting them, and then harvesting the virus. This process can only produce a limited quantity of the virus and thus is not suitable for application in large areas. It is also believed to be suitable only for high populations of gypsy moth and would not be suitable for eradication of gypsy moth in B.C.

No Treatment

If pheromone trapping results determine that a small but isolated population exists in a particular area, the decision to apply treatment measures may be delayed. Instead of treatment, the trap density may be intensified to further define the area of infestation. In many cases, such small populations may not persist and die out on their own (see trapping history page). The decision to delay treatment is site specific and can be due to many factors like initial trapping density, host availability, suitability of the climate, location of the infestation, etc. This option is the most commonly used in B.C. and shows that most introductions are rarely successful.  However, when there is evidence of a growing population, treatments will likely be conducted.  

Source: Fraser, B.D. and Agriculture and Agri-Food Canada. 1994. Draft Management Plan for the North American Gypsy Moth in British Columbia. 35 pp.

Gypsy Moth Homepage > Management Options > Description of the Eradication Strategy > monitoring > Selecting a Treatment > Aerial Spraying with Btk > Detailed Information on Aerial Spraying > Ground Spraying > Alternative Treatments > public involvement

Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests and Range
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136