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Winter Tree Care: Identifying Common Tree Insects in Winter, Part 8

This is the eighth and final part of a series on winter tree insects. This article examines the snow fly and winter moth.

Introduction

Through the winter months, plants conserve their energy, often enduring inclement weather in anticipation of spring. Due to the frigid temperatures, many insects enter a state of dormancy, overwintering on or within their hosts. While some insects are visible during winter, others conceal themselves in bark crevices or beneath the soil surface. The following examines some of the most common insects to infest trees during winter, and how they may be observed.

Snow Fly (Chionea)

The snow fly is a wingless crane fly in the genus Limoniid. It is notable for being one of the few insects to remain active during the winter months. The insect’s idiosyncratic anatomy enables it to survive in sub-freezing temperatures. The snow fly was first described in Alberta, Canada. At least 40 species of snow fly have since been discovered across the Northern hemisphere. When they are present, snow flies can often be observed quickly navigating across the snow and ice in search of mates. Snow flies are not believed to feed on live plant material. As such, they are not considered plant nuisances.

Hosts

Snow flies do not seek out any particular hosts to feed in, or lay their eggs on.

Management

  • Snow flies do not cause damage to plants. They do not require management.
  • Rock crickets (Grylloblattidae) are the snow fly’s most common natural predator. When they are both present in an area, rock crickets help to significantly reduce snow fly populations.
  • Snow flies are consumed by mice, rats, and winter birds.
  • Snow fly eggs are eaten by numerous beetle grubs, caterpillars, and fleas.
  • The larvae can be infested by a tapeworm species. The tapeworm is believed to come into contact with the larvae when they feed on mice feces.
  • A species of nematode has been found to sometimes parasitize the larvae and adults.

Winter Moth (Operophtera brumata)

Winter moth is a small species of moth native to Europe and Western Asia. It was first discovered in North America in the 1930’s, appearing across various regions of Canada. It is now considered an invasive pest that is capable of defoliating maples, oaks, and other deciduous trees.

Symptoms of Infestation

Winter moth larvae wriggle their way into tree buds in early spring just before they bloom. Once inside, they begin to feed, devouring the flower and foliar buds. As the larvae grow, they feed in the expanding leaf clusters, stripping the tree of any new bud growth. Large populations can quickly defoliate trees, resulting in limb or tree failure. The decimation of buds on fruit trees can result in fewer fruit being produced, leading to dimished harvests.

Management

  • Every spring, have a professional arborist perform a thorough inspection of the leaf buds on any susceptible trees.
  • Any trees that are stressed should be supplemented with water throughout the entire growing season.
  • Chemical compounds and oil sprays can be effective at preventing winter moth. Applying a dormant oil spray to trunks and branches can kill eggs before they hatch. However, depending on their location, some eggs may be shielded from the application. Chemical compounds such as spinosad or carbaryl can be used to contend with newly hatched caterpillars, but they have their drawbacks. Spinosad in particular is effective against winter moth, but it is highly toxic to honey bees. Any chemical compounds that are used should be applied after trees have come into bloom and bees have finished foraging.
  • Chemical insecticides, such as pyrethroids, are often used to eradicate winter moth, but they can have an adverse effect on other more beneficial organisms as well.
  • Tree banding involves the installation of a paper or plastic band around the trunk of a tree. The band is covered with a sticky substance that snares caterpillars as they attempt to climb up the tree. A cotton or polyester fiberfill can be placed under the band in order to further discourage passage. These products are not often effective, and can be easily overwhelmed when used on larger populations.
  • Wasps, beetles, and the tachinid fly are a few of winter moth’s natural predators. When present in an environment, they can lead to an increased mortality rate in winter moth pupae. However, they do not significantly hamper the development of larger populations.

Photo courtesy of Ben Sale CC-by-2.0

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