How British Columbia is Managing Gypsy Moth Populations


 |  Biodiversity/Conservation

How British Columbia is Managing Gypsy Moth Populations


Invasive species are organisms that are not native to a particular habitat and can cause a broad range of negative impacts on the environment and economy. One such way is by reproducing and populating new habitats, which can disrupt native ecosystems and impact endemic species populations that are local to that area. A variety of invasive species have been introduced into British Columbia over the years, including the gypsy moth. 

In the caterpillar phase of their life cycle, the gypsy moths’ normal habitat is on hardwood trees, such as maple trees. 

Gypsy Moth Biology - Province of British Columbia

The life cycle of a gypsy moth.

They infect many hardwood species across B.C. and cause vast amounts of economic damage, estimated at up to $868 million in economic losses. Gypsy moths were first introduced into B.C. in 1912 on young cedars imported from Japan. The larvae can also be spread through wind or human transport.


In B.C., the Gypsy Moth Technical Committee is responsible for managing local gypsy moth infestations. One of their solutions is to aerial spray sections of infested land with Foray 48B, an insecticide. This solution has been used in the past and is currently in use in specific areas of B.C., including in the Courtenay area. There are various advantages and disadvantages to the current gypsy moth treatments in B.C.

Pros – Effects on the Environment

Gypsy moths are considered to be a highly destructive invasive species. The gypsy moth is able to lay larvae on the leaves of several hundred plant species, such as oak trees, aspen, and willow trees. A single gypsy moth is capable of laying hundreds of larvae. The rapid population growth of the larvae contributes to the widespread loss of leaves, known as defoliation, causing multi-million dollar damage to the economy. Defoliation also reduces the amount of photosynthesis that plant species can undergo, thereby limiting food supply for other species and impacting the plants’ ability to sequester carbon. Defoliation also weakens trees by increasing their susceptibility to weather changes, other pests or diseases (as trees must now divert their energy from growing to defending themselves).

A specific subspecies of the gypsy moth, the Asian gypsy moth, is a threat particularly to Canadian forests. The Asian gypsy moth thrives in Canada’s colder climate and prefers to feed on coniferous trees. Canadian forests contain an abundance of conifers, including pines, yews, and hemlocks.

Furthermore, the physiology of the gypsy moth larvae can also cause harm to other organisms. The bodily fluid of gypsy moths is lethal, often leading to the death of swallowtail caterpillars. These caterpillars also feed on hardwood trees but do not cause significant damage. They rely on leaves for their food supply, which have been decreased significantly due to defoliation by gypsy moths.  The caterpillars have also been found to have an increased susceptibility to parasites when they were nearby gypsy moth populations. Additionally, the hairs on a larva produce a poison ivy and any form of human contact, whether direct or indirect, can cause a severe rash. 

Correlations with Climate Change:

The spike in gypsy moth populations may be attributed to changes in climate. For instance, in their normal life cycle, the larvae cannot survive at low temperatures. However, as climate change increases temperatures, larvae growth increases rapidly, especially above 32°C. Additionally, areas that receive low rainfall may have higher populations of larvae as the eggs remain dry and are able to progress in their life cycle up to and beyond the larva stage. Areas with high enough precipitation may notice a decrease in gypsy moth populations as the rain drowns the larvae.

Cons – Effects on Human Health

However, gypsy moth treatments also have several disadvantages. The particular spray used in aerial spraying, Foray 48B, has shown to have various health effects on humans. One study examined the effects on hundreds of participants that were beneath a Foray 48B spray zone, and many displayed a range of symptoms from an irritated throat to sleep problems. 

Aerial spraying also has its drawbacks. Wind can carry spray droplets into unintentional areas that otherwise have not been notified of the spraying beforehand by the government. It can also cause environmental damage and impact human health as noted above. This can also lead to an increase in operational costs if the spraying is inaccurate and product is wasted.

Furthermore, gypsy moth populations take several years to populate before any noticeable defoliation occurs. Therefore a spray such as Foray 48B used quite commonly in B.C. may be a drastic solution, whereas B.C. could refocus our outlook to examine more proactive and preventative measures. For instance, pheromone traps can be installed to prevent male moths from mating and thereby limiting population growth. Also, susceptible trees can be wrapped in burlap to prevent defoliation.


Although gypsy moths have been labelled as a highly destructive and invasive species, the current treatments in use by the B.C. government may also have negative consequences. A solution is to change our outlook to focus on more preventative measures, rather than reactive measures.