Department Update on Gypsy Moths
The County of Middlesex Forestry staff are aware of gypsy moth occurrences within the Skunks Misery Forest and continue to monitor the situation. Although the gypsy moth is an invasive species, it has evolved to a state of naturalization within Ontario which means that it cannot feasibly be eradicated and there will be population outbreaks. As the population dynamics of this invasive insect reach their peak, natural predators and pathogens (including fungi, wasps, and the NPV virus) are expected in turn to significantly affect and reduce gypsy moth population numbers. This cycle has been observed elsewhere in the County where populations peaked in 2019 and 2020 and are now dropping.
In diverse, relatively undisturbed forest ecosystems, such as Skunks Misery, large healthy trees should be able to tolerate two or three defoliations before they suffer significant impacts. Although in nature many variables affect ecosystem trajectories, there is general consensus that gypsy moth outbreaks and defoliation are not anticipated to cause substantial crown dieback or mortality. Assuming that weather conditions continue to be favourable, the majority of healthy trees are expected to re-foliate either later in the summer or next spring.
The County continues to monitor the situation and work with the OMNRF Forest Health staff who will again conduct aerial surveys this summer to monitor forest health conditions on a landscape scale. If the public is aware of specific areas where large numbers of Gypsy Moth are found, please contact Forestry staff to identify them for site monitoring purposes.
There are a number of resources available online related to Gypsy Moths, including the Ontario Ministry of Natural Resources and Forestry's website and the links below.
The County of Middlesex Area Weed Inspector is also the Municipal Weed Inspector for all eight local municipalities in the County. Responding primarily to complaints, the Area Weed Inspector works with staff from local municipalities, the Ministry of Transportation, Hydro One, Railways and other agencies to bring weed concerns to their attention.
The Weed Act applies only to noxious weeds that are growing in close proximity to agricultural crop lands and commercial horticultural lands. Noxious weeds growing in urban areas can be addressed through local property standards by-laws. A Form 1 Weed Order can be issued against the property owner; however, voluntary compliance is the most common remedy.
Giant Hogweed can be a serious health hazard for humans. Its watery, clear sap contains photosensitizing compounds, which, when in contact with human skin and in combination with UV radiation, can cause burning. Content varies depending on the part of the plant, but contact should be avoided at all times. The reaction of the skin depends on individual sensitivity.
Emerald Ash Borer
To slow the spread of the emerald ash borer (EAB) to new areas, the CFIA uses measures to control the movement of potentially infested materials. People who move regulated materials from regulated areas without the permission of the CFIA could face fines and/or prosecution.
In addition to the regulated areas listed above, the movement of materials can also be regulated through legal notices issued to property owners. For properties where EAB has been confirmed, a Prohibition of Movement is issued, which prohibits the movement of regulated materials from that specific property. Contact your local Canadian Food Inspection Agency office for additional information and view a map of regulated areas.
The Gypsy Moth is a non-native insect from Europe that was introduced to North America in the 1860s. The insect has become naturalized to Eastern North America, including Middlesex County. It has spread widely in areas where Oak is found, its preferred host tree species, in both rural and urban ecosystems. The gypsy moth feeds on more than 300 species of trees and shrubs including Aspen, Birch, Cedar, Cottonwood, Fruit trees, Larch, Oak (preferred host), Poplar, and Willow.
This insects’ population dynamics can be described as boom and bust, where every 8-12 years, the population within certain areas will reach epidemic proportions only to collapse again and remain at endemic levels for another eight years or so. Gypsy moth outbreaks may appear suddenly and may continue for two to five years in a location. During a population outbreak, the caterpillars in very large numbers can be observed feeding within trees, defecating, and dangling from silk threads.
The Gypsy Moth spreads as egg masses are inadvertently moved on firewood, cars, trucks, trailers, RV's, boats, ATV, etc. If the relocated eggs hatch in their new location and they find host trees a new population will occur. It is important to inspect all items that are moved to and from locations that may have the Gypsy Moth.
Figure 1: Photo of young caterpillar on the right and mature caterpillar on the left with characteristics red and blue spots (photo M Brown)
Newly hatched caterpillars are about half a centimetre long and dark in colour. European Gypsy Moth caterpillars grow and change in appearance over the span of one to two months. As they grow, they moult or shed their skin. By the fourth moult, the pairs of characteristic blue and red dots are visible on their back and they are about six to seven centimetres in length.
In contrast to trees within a rural setting, trees in urban settings are typically exposed to additional environmental stressors such as drought, altered hydrology, compacted soils, fragmentation, pesticides, air pollutants, and fewer natural predators. These additional stresses can expose urban forests, parkland trees, boulevard trees, and private yard trees to an increased level of damage as they may have limited resources to draw from during the recovery phase following defoliation.