Winter Moths

Life Cycle of the Winter Moth (Operophtera brumata)

  • Introduction

    • Invasive insect introduced from Europe to the United States via Canada.

    • Most commonly observed:

      • Late fall to early winter as an adult white moth.

      • Spring as a tiny green caterpillar.

Adult Moths and Egg Laying

  • Emergence

    • Adult winter moths emerge from the ground in November or December.

    • Only males can fly, while females climb trees/buildings.

    • Males are attracted to females by pheromones emitted by females.

  • Mating and Egg Laying

    • After mating:

      • Females lay approximately 150 eggs under tree bark or in crevices.

      • Lifespan of the female ends after egg-laying.

Caterpillar Development

  • Hatching

    • Eggs hatch in March or April into smooth green inchworms with narrow white stripes.

  • Feeding & Dispersal

    • Caterpillars use silk strands to balloon into tree canopies.

    • They cause damage by feeding on tree buds and leaves.

    • Often drop to nearby shrubs like roses when feeding.

  • Pupation

    • After feeding ends in mid-June, caterpillars migrate to the soil to pupate and emerge as moths.

Impact of Winter Moths

  • Defoliation

    • Most visible effect of winter moths:

      • Significant defoliation of trees and shrubs in spring.

    • Affected trees in Massachusetts include:

      • Maple, oak, ash, and various fruit trees (apple, crabapple, blueberry).

  • Damage Severity

    • Heavily infested trees may become completely defoliated.

    • Healthy trees can produce a second set of leaves, but this causes stress.

    • Research indicates:

      • Complete defoliation can reduce oak species' growth rates by up to 47%.

      • Successive defoliations can kill branches or entire trees.

  • Environmental Factors

    • Prolonged cool springs allow more feeding time for caterpillars.

    • Drier years increase tree stress.

    • Infestations of other pests and diseases can worsen tree health.

Controlling Winter Moths

  • Natural Control

    • Parasitic flies (Cyzenis albicans) are being used to combat winter moth populations:

      • Flies lay eggs on leaves eaten by caterpillars.

      • Larvae consume the caterpillar from within, causing death.

      • Fly pupates inside the dead caterpillar.

  • Homeowner Actions

    • Check for inchworm caterpillars in April.

    • Minimize damage with the following methods:

      • Supplemental watering to help trees recover.

      • Use sticky banding traps around tree trunks to catch adults.

  • Limitations of Control Methods

    • B.t. (Bacillus thuringiensis kurtstaki) can kill young caterpillars but may also harm native butterflies.

    • Sticky bands can become ineffective quickly and may not prevent egg-laying.

    • Additional sprays are recommended for fruit orchards to prevent damage.

Conclusion

  • Awareness of winter moth life cycle and damage can help mitigate their impact on local ecosystems.

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