Western tussock moth

The Western tussock moth (Hemerocampa vetusta) belongs to the family Erebidae, subfamily Lymantriinae. It is a significant defoliator native to western North America, recognized primarily by the unique appearance of its larvae, which possess distinctive tufts of hair that can cause skin irritation in humans.

This pest affects a wide range of host plants, including various deciduous trees and shrubs. It is frequently observed on fruit trees such as apples and pears, as well as native forest species including oaks, alders, and willows. The versatility of its diet makes it a persistent threat in both managed landscapes and natural woodlands.

The moth typically completes one generation per year. The eggs overwinter on the bark or the remains of old cocoons. Larvae emerge in the spring, coinciding with the flushing of new foliage. After undergoing several larval instars, they pupate, and adult moths emerge later in the season. Notably, females are wingless, which affects their dispersal patterns.

Damage is characterized by heavy defoliation. Early-stage larvae skeletonize leaves, while later instars consume entire leaf blades, often leaving only the major veins. Severe infestations can cause significant stress to trees, reducing growth rates and fruit production. Repeated defoliation over consecutive years may lead to tree mortality.

Management strategies require a multifaceted approach to be successful. Key practices include the physical removal of egg masses during the dormant season. Chemical control with insecticides is often reserved for heavy outbreaks, preferably focusing on younger larvae. Integrated pest management (IPM) guidelines include:

• Monitoring populations using pheromone traps.
• Promoting natural predators and parasitoids.
• Applying Bacillus thuringiensis (Bt) during the early larval stages.
• Utilizing sticky barriers to prevent larvae from climbing trunks.