White-marked tussock moth

The White-marked tussock moth (Orgyia leucostigma) belongs to the family Erebidae. It is a well-known defoliator that affects a wide variety of deciduous trees and shrubs throughout North America. Understanding its biology is key to preventing major damage in orchards and ornamental gardens.

This pest has a vast host range, including fruit trees like apple, pear, and plum, as well as various shade trees such as maple, oak, and elm. The caterpillars are highly polyphagous, meaning they can thrive on different plant species, which allows them to easily migrate between nearby vegetation in the garden.

The lifecycle is distinct due to the flightless female moths, which lay their eggs directly on the cocoon from which they emerged. These egg masses are covered in a protective white frothy material, making them easier to spot during the dormant season. Caterpillars are easily identified by their bright yellow, red, and black markings along with distinctive hair tufts.

Feeding damage begins early in the spring as larvae chew on emerging buds and young leaves. As the caterpillars grow, their appetite increases, often leading to severe defoliation. Besides the direct loss of leaf surface, the irritating hairs on the caterpillars can pose a health risk, causing contact dermatitis in humans and pets.

Control strategies should be multi-faceted. Manual removal of overwintering egg masses from branches is a highly effective cultural control method. For larger infestations, biological insecticides containing Bacillus thuringiensis are recommended as they target the larvae specifically, minimizing impact on beneficial insects and the environment.