Insects and Pathogens
With the onset of climate change, more warm and wet weather pests are moving into New England. Migratory insects are arriving earlier with earlier snowmelt and rising air temperatures, and insects that are only marginally-adapted to the region are beginning to invade as the climate warms. Increases in balsam woolly adelgid, spruce budworm, Beech bark disease, and winter moth are already causing serious injury and death of large tree populations. Inadequate winter chill will adversely affect agriculture by increasing populations of insects and disease, including flea beetle and Steward’s wilt. Wetter conditions will also increase the likelihood of white pine needle disease caused by pathogenic fungi.
Maine has been invaded by many exotic and destructive species beginning with the colonization of the North American continent via the import, both accidental and deliberate, of European and Asian species. Non-native invasive species compete for natural resources and alter the native dynamics of forests, wetlands, rivers, lakes, and ponds. Some of these non-native species have been in New England since the beginning of colonization but most have arrived in recent decades by the increase in overseas and local commerce. They spread mainly by transport on boats, trucks, birds, animals, and plants. Changing climatic conditions, including shorter winters, reduced snowpack, and increased air temperatures, allow increased survival of non-native species and expedite the spread of more southern species into New England. Before European settlement, insect and disease outbreaks in forests were caused by native species such the spruce budworm and forest tent caterpillar. More recently, insect and disease outbreaks have occurred at an increasing frequency because of the introduction of non-native insects and disease agents. The introduction of the hemlock woolly adelgid insect has caused complete mortality of eastern hemlock in parts of Massachusetts and Connecticut, and this damaging pest has now crossed the Maine border. In addition to damaging insect pests, the introduction of earthworm species by the colonists into previously-glaciated regions of the northeast has dramatically altered soil composition and structure, changed organic matter decay rates and processes and made seedbed and germination conditions less favorable for some native plants.
Of great concern is the invasive emerald ash borer (Agrilus planipennis), which was first seen in northern Aroostook County, Maine in the spring of 2018. Several more sightings were reported in western York County, Maine in the fall of 2018. The emerald ash borer (EAB) is an Asian, wood-boring beetle that has cleared a destructive path in 45 states (including the entire eastern seaboard, except Florida) and four Canadian provinces. It likely hitchhiked to North America across oceans in packing crates and shipping materials (Cappaert, Mccullough, Poland, & Siegert, 2005). It is the lifecycle of EAB that is so perilous for trees. The adult beetle lays its eggs in the cracks of ash trees (Fraxinus sp.). When the eggs hatch, the larvae burrow into the tree and feed on the inner bark and phloem, which disrupts the transport of nutrients and water throughout the tree. The beetle’s eating pattern creates distinct “S”-shaped carvings in the bark. In Maine, there are three species of ash trees, and this beetle poses a threat to all of them. Preference is given to black and green ash (Fraxinus pennsylvanica and Fraxinus nigra) and to trees that are already compromised or sick. When trees are infected, leaves sprout from roots and trunks, bark splits, and the canopy dies.
Loss of black ash trees in Maine will not only have ecological impacts but cultural impacts as well. The black ash tree is a cultural keystone species and an important economic resource for the Wabanaki people, who use black ash trees for basketmaking.
Communities have learned a lot in the last seventeen years since EAB was first sited in the Midwest in 2002. Although climate change is enhancing the EAB’s preferred habitat into northern regions like Maine, Maine is also in a unique place to have a delayed invasion of EAB by taking advantage of research and trial and error management strategies used in other states. Non-infested communities should monitor and prepare for the spread of the invasive beetle to ensure early detection and action. Sticky, purple traps can be set out to trap and monitor for the EAB. Woodpeckers and wasps are natural predators and natural monitors for the EAB because they feed on the EAB and will increase activity on host trees. Firewood has been cited as the predominant mode of travel for the EAB, so it is critical that vacation communities like those of Kezar Lake be extremely vigilant about people bringing in firewood from other places in Maine or other states. When the EAB is found in an area, property owners or land managers can selectively harvest ash trees to reduce the food source and employ biological controls on the EAB, such as increasing the populations of native woodpeckers and native or imported parasitic wasps.
The Surveillance, Outreach, Involvement section on Maine’s EAB page (www.maine.gov/EAB) provides a wealth of resources for getting involved with state-wide monitoring efforts. The State of Maine takes responsibility for the mitigation of invasive insects with integrated pest management tools, including prescribed fire, mechanical treatments, and herbicides. If Maine communities work together, it is possible to mitigate the risks associated with these invasive insects to ensure sustainable native populations and tree resource for decades to come.
A compilation of invasive species threatening Maine is provided in Appendix B of the 2018 CCO Annual Report, including aquatic fauna, wetland plants, algae, forest fauna, and forest insects. A description and image of each invader is provided, along with sources for more information on each species’ identification and mitigation.
The Maine Center for Disease Control and Prevention (Maine CDC) data shows that the number of reported Lyme disease cases in Maine is increasing. This increase in reported cases is likely due to a combination of climate-induced factors. Warming air temperatures (especially in winter), more precipitation, a longer growing season, and a proliferation of their primary hosts (mice, chipmunks, and other small mammals) are promoting the northern migration of and thus increasing populations of disease-carrying ticks in the state. Although deer, moose, and other large mammals are also hosts to ticks, small mammals are considered their primary hosts and generate a far greater threat to humans because small mammals live closer to where we live, work, and play.
Deer ticks carrying Lyme disease can be found in wooded areas or open, grassy areas, especially along the edges of forests. To best control tick populations around your property, clear brush and leaves and deter deer, mice, and chipmunks. Be vigilant in checking for ticks and seek immediate medical help if you were bitten by a deer tick. Lyme disease can be easily treated with antibiotics, but if left untreated, can cause severe illness, arthritis, and neurological problems.
There are several other tick-borne diseases that threaten public health and may increase with a changing climate. These include anaplasmosis, babesiosis, ehrilichiosis, powassan virus, spotted fever rickettsiosis, as well as other less common diseases. Each of these has shown an increase over the years, especially anaplasmosis. A study conducted by the University of Maine’s Cooperative Extension Tick Lab found that 40% of the 2,000 deer ticks tested in 2019 were positive for Lyme disease (8% were positive for anaplasmosis and 16% were positive for babesiosis).
For more information on prevention and treatment, please visit https://www.cdc.gov/ticks and http://www.maine.gov/dacf/php/gotpests/bugs/ticks.htm. Ticks can be submitted to the University of Maine’s Cooperative Extension Tick Lab to be tested for a small fee. Contact the lab by emailing tickID@maine.edu or by calling 207-581-3880.