**Hawthorn Lace Bugs** (*Corythucha cydoniae*) are small, highly ornamental insects that are pests primarily of plants in the Rosaceae family, including **hawthorns, cotoneaster, pyracantha, and apple**. They are named for the intricate, lace-like appearance of their wings and pronotum. Lace bugs are piercing-sucking insects that feed on the underside of leaves, causing aesthetic and minor health damage characterized by severe leaf stippling, discoloration, and premature leaf drop.
Taxonomy and Classification
Hawthorn Lace Bugs belong to the order Hemiptera (true bugs), family Tingidae. They undergo incomplete metamorphosis. They are highly specialized feeders, relying on their specific host plants. They are typically sedentary once established on a leaf, often forming dense colonies.
Physical Description
Adult Lace Bugs are tiny, flat, rectangular, 1/8 to 1/4 inch long.
- **Appearance:** Easily identified by the ornate, gauze-like wings and hood (pronotum), which are white or translucent and cover most of the body.
- **Nymphs:** Dark, spiny, and wingless, often found in clusters with adults and eggs on the leaf underside.
- **Damage Sign (Topside):** Severe **stippling** (tiny white or yellow dots) across the upper surface of the leaves. In heavy infestations, the leaves turn prematurely gray, yellow, or bronze.
- **Damage Sign (Underside):** The underside of the leaf is contaminated by small, shiny, black/brown, varnish-like droplets of frass (fecal matter) and cast nymphal skins.
Distribution and Habitat
Hawthorn Lace Bugs are widely distributed across North America, coinciding with the range of their host plants. Their habitat is the foliage of host trees and shrubs. They overwinter as adults, often tucked into bark crevices, debris, or curled leaves near the host plant.
Behavior and Conflict
Both adult and nymph lace bugs use piercing-sucking mouthparts to extract chloroplasts and nutrients from the leaf cells.
- **Aesthetic Damage:** The primary conflict is the destruction of the leaf’s green chlorophyll, resulting in the characteristic stippled, faded appearance, which reduces the ornamental value of landscape plants.
- **Health Stress:** Heavy, chronic infestations can reduce the plant’s photosynthetic capacity, leading to premature leaf drop, reduced vigor, and increased susceptibility to other stresses (like drought).
- **Messy Frass:** The concentrated, sticky, black frass on the leaf undersides, and potentially on objects below the tree, is visually unpleasant.
Management and Prevention
Control is integrated pest management (IPM), targeting the insects on the leaf undersides early in the season.
- **Monitoring:** Inspect the underside of leaves frequently, starting in late spring, particularly on susceptible hosts.
- **Cultural Control:** Ensure plants are well-watered and fertilized, as healthy plants are more tolerant of damage. Prune out dense interior growth to improve air circulation.
- **Horticultural Oils/Soaps:** Apply insecticidal soap or narrow-range horticultural oil, ensuring thorough coverage of the **undersides** of the leaves where the insects hide and feed. These are most effective against young nymphs.
- **Systemic Treatment:** In high-value, chronically infested trees, a soil-applied systemic insecticide may be used to protect the foliage throughout the season.
Conservation and Research
Hawthorn Lace Bugs are managed as landscape and ornamental pests. Research focuses on identifying resistant varieties of hawthorn and other host plants, and exploiting natural enemies (like minute pirate bugs) for biological control in landscape settings.