How Do New York’s Pests & Diseases Survive Winter?

I can’t help but think about the forest pests and diseases that I work with, and how they fare in winter weather.

We know that monarch butterflies migrate to avoid our cold winters, but what about the insects that stay put? Many of our forests pests and diseases have adaptations and strategies to survive the cold.

Emerald ash borer (EAB): Emerald ash borer spends the winter in the sapwood of ash trees. The tree’s outer bark acts as insulation, keeping temperatures inside the tree warmer than the outside air. EAB larvae use a strategy called “supercooling” to survive the winter. They can cool their body fluids below its normal freezing point without actually freezing. They do this by producing “antifreeze” proteins that prevent the water in their bodies from freezing.

Southern pine beetle (SPB): Southern pine beetle also spends the winter in the bark of the tree, where they are protected from the harsher outside temperatures. They can overwinter at any life stage, but the most cold-tolerant life stage is the mature larvae, or prepupae. Southern pine beetle will continue to grow throughout the winter. However, when temperatures get too low (around -16C), SPB will die.

Asian longhorned beetle (ALB): Asian longhorned beetle can overwinter at any life stage. Inside the tree, the larvae go through diapause, where they become dormant and stop developing. The larvae are also freeze tolerant, meaning they can freeze, but they create proteins and cryoprotectants to limit how much ice forms in their bodies. On the other hand, the eggs are freeze avoidant; like EAB, they can lower the freezing point of internal liquids.

Spongy Moth: Spongy moth endures the winter in the egg stage of its life cycle. In late summer/early fall, the moths lay eggs and cover them in fuzzy silk. The eggs are freeze-avoidant, meaning they prevent internal liquids from freezing with antifreeze proteins. The surface that the egg masses are laid on, such as trees or rocks, can also insulate them from colder temperatures.

Hemlock woolly adelgid (HWA): Hemlock woolly adelgid remains active throughout the winter. In their nymph stage, they attach to the base of the twigs through their sucking mouthparts. During these winter months, they continue to feed on the tree, exuding a white, waxy wool to help protect them from the elements. This wool makes them much more visible, making winter an easy time to survey for HWA. By March, they have developed into adults and begin to lay eggs. Because they are still exposed, HWA can die in extremely cold temperatures.

Oak wilt: In cold temperatures, many fungi go into a dormant state. When temperatures warm up again, they resume growth. The oak wilt fungus overwinters under the bark of living trees or as fungal mats on dead trees. The vectors of oak wilt, nitidulid beetles, are also dormant in the winter. It is best to prune oak trees in the winter while the beetles are not active to prevent the disease from spreading.

Beech leaf disease (BLD): The nematode that is associated with BLD can overwinter in buds on the tree or leaves on the ground. Nematodes typically overwinter as eggs. Some species live in the artic and are very cold tolerant. They employ the same strategies as insects, supercooling, to limit the formation of ice crystals in their bodies. Since the nematodes overwinter in buds with the developing leaf tissue, BLD symptoms are visible from the moment leaves emerge in the spring.

Whether it’s laying low beneath the bark or in the buds of a tree, producing a white waxy coat, or changing their body chemistry to handle freezing, forest pests, and pathogens have a variety of methods to handle New York’s winter weather.

Erica Culbert is the Lab Assistant at the NYS DEC Forest Health Diagnostic Lab.

Photo of Hemlock woolly adelgid provided.