**Peach Twig Borers** (*Anarsia lineatella*) are small, widely distributed moths and a major pest of stone fruits, especially **peaches, nectarines, plums, and apricots**. The damage is caused by the larval stage (caterpillar), which bores into new terminal shoots (twigs) early in the season, causing them to wilt and die (**flagging**), and later bores into the developing fruit, contaminating it and reducing marketability. They have multiple generations per year, requiring season-long monitoring.
Taxonomy and Classification
Peach Twig Borers belong to the family Gelechiidae in the order Lepidoptera (moths and butterflies). They undergo complete metamorphosis. The caterpillars are the destructive stage. The moth is considered a significant, direct pest because its damage affects both the structure of the tree and the quality of the marketable fruit.
Physical Description
The adult moth is tiny, with a wingspan of about $1/2$ inch.
- **Adult Moth:** Grayish-brown with scattered darker scales, giving a mottled appearance. They are nocturnal and rarely seen.
- **Larvae (Caterpillars):** Small, dark brown to blackish with alternating light and dark bands (annulations) on the segments, and a black head. They grow up to $1/2$ inch long.
- **Overwintering Site:** Larvae overwinter in tiny, protective silk-lined chambers (**hibernacula**) built under the bark of crotches and spurs, making early-season control crucial.
- **Damage Sign:**
- **Flagging:** Wilted terminal shoots, often with sawdust-like frass protruding from the entry hole in the twig, is the key sign of the first generation’s activity.
- **Gummy Frass:** Entry holes in fruit exude gum and frass, leading to damaged, unmarketable produce.
Distribution and Habitat
Peach Twig Borers are found globally in all major stone fruit-growing regions. Their habitat is restricted to stone fruit orchards and landscapes. They are especially problematic in warm climates where they can complete three or four generations per season.
Behavior and Damage
The first generation emerges from hibernation during the bloom period.
- **First Generation Damage:** Larvae emerge and bore directly into the new terminal shoots, destroying the growing tip. This causes the shoot to wilt (“flag”), leading to excessive branching and reduced tree structure.
- **Later Generation Damage:** Subsequent generations bore directly into the developing fruit, usually near the stem or where two fruits touch. This internal feeding contaminates the flesh and can introduce pathogens, often leading to total loss of the infested fruit.
- **Multiple Generations:** The short life cycle and multiple generations mean that control measures must be consistently applied throughout the growing season, timed to coincide with the beginning of each larval hatch.
Management and Prevention
Control is integrated pest management (IPM), relying heavily on pheromone monitoring and targeted application.
- **Monitoring:** Pheromone traps are used to catch male moths to track the start of each generation’s flight period and determine the optimal timing for controls.
- **Mating Disruption:** High densities of pheromone dispensers can flood the orchard environment, confusing the males and preventing them from finding females for mating.
Conservation and Research
Peach Twig Borers are managed as a continuous, high-impact pest. Research focuses on improving mating disruption technology, developing microbial controls (e.g., specific strains of *Bacillus thuringiensis*), and breeding fruit varieties with greater resistance to borers.