Braconid Wasps
Braconidae
parasitoid · caterpillar parasitoid · both
Last updated
Braconid wasps are small parasitoid wasps that lay eggs inside living hosts, primarily aphids, caterpillars, and leafminers. The developing larva consumes the host from within, eventually killing it. Females of some species can parasitize over 200 aphids per day, making braconids among the most effective natural enemies in managed landscapes.
Most braconids in the Puget Sound region are native, though several commercially available species are used in augmentative biocontrol. The tiny mummified aphid husks left behind after parasitism are a reliable sign these wasps are active in your garden. Avoiding broad-spectrum insecticides, especially neonicotinoids and pyrethroids, is the single most important step for conserving them.
Target Pests (12)
Quick Reference
Identification
Adult Description
Small to medium parasitoid wasps, typically 2–15 mm body length (most species under 10 mm). Slender body with narrow waist. Antennae typically shorter than ichneumonids, with 16+ segments. Wing venation reduced compared to ichneumonids (fewer closed cells). Most species dark brown to black; some Aphidiinae pale or yellowish. Ovipositor shorter than in ichneumonids. Adults observed visiting flowers for nectar (WSU HortSense Wasps; Britannica).
Larval Description
Legless endoparasitic larvae developing inside host body. Feed on hemolymph and tissues. Some braconid subfamilies (e.g., Microgastrinae) produce external cocoon masses on or near the host cadaver—visible as clusters of white or yellow silk cocoons on caterpillar bodies (diagnostic sign of parasitism). Aphidiinae larvae develop inside aphids, causing the aphid body to harden and inflate into a characteristic golden-brown 'mummy' (WSU HortSense; Britannica).
Size Range
2–15 mm body length (most species under 10 mm)
Key Features
Smaller than ichneumonids on average; reduced wing venation (fewer closed cells); shorter ovipositor. Some species produce visible external cocoon masses on parasitized caterpillars. Aphid mummies (swollen, golden-brown aphid bodies) are diagnostic evidence of Aphidiinae activity.
Lifecycle & Phenology
Complete metamorphosis: egg, larval instars, pupa, adult. Females inject eggs into host bodies using ovipositor. Many species also inject polydnavirus during oviposition, which suppresses host immune responses and arrests host development. Larvae develop internally as endoparasitoids. In caterpillar-parasitizing subfamilies, mature larvae exit the host and spin external cocoons nearby. In Aphidiinae, the parasitoid pupates inside the host aphid body, creating a characteristic 'mummy.' Adults emerge and feed on nectar, pollen, and honeydew. Multiple generations per year. The Aphidiinae subfamily (aphid parasitoids) are among the most important natural enemies of aphids in PNW landscapes (WSU HortSense Wasps; Britannica).
| Generations per Year | Multiple; Aphidius species can complete a generation in 10–14 days under warm conditions (commercial biocontrol literature) |
| Overwintering Stage | pupa |
| Egg Capacity | Females can lay up to 200 eggs per day under optimal warm conditions; lifetime fecundity varies by species (Britannica) |
| Larval Duration | [DATA GAP]—varies by species, host, and temperature |
| Development Duration | Aphidius colemani: approximately 10–14 days egg to adult at 20–25°C (commercial biocontrol literature) |
| Adult Lifespan | [DATA GAP] |
| Active Months | March through November; Aphidiinae active whenever aphid hosts are present |
Habitat & Conservation
Adults require nectar and pollen from open-structured flowers for sustenance and egg maturation. Apiaceae and Brassicaceae are documented as preferred food plant families. Habitat structural diversity (hedgerows, diverse plantings) supports host-seeking behavior. Aphid mummies in foliage are evidence of active populations. Extremely sensitive to broad-spectrum insecticides (WSU HortSense; Xerces Society 2014).
Nectar & Pollen Sources
Conservation Practices
- Permanent insectary strips with Apiaceae for adult nectar provisionTiming: Established in fall or early springAdult females require nectar for egg maturation; proximity to nectar sources increases parasitism rates in adjacent areas (Landis et al. 2000; Xerces Society 2014)
Pesticide Sensitivity
| Product Class | Impact | Notes |
|---|---|---|
| Neonicotinoids imidacloprid, thiamethoxam | lethal | Systemic neonicotinoids toxic to nectar-feeding adults. Aphidius colemani exposed to contaminated aphid hosts (Xerces Society 2016; Hopwood et al. 2016) |
| Pyrethroids bifenthrin, lambda-cyhalothrin | lethal | Broad-spectrum contact toxicity; Diachasmimorpha longicaudata shows 100% mortality within 96 hours at field rates (Journal of Economic Entomology 2021) |
| Spinosad spinosad | lethal | Aphidius colemani is nearly 20-fold more susceptible to spinosad than to imidacloprid—notably more toxic to braconids than to many other beneficial groups (Biondi et al. 2018) |
| Horticultural oils mineral oil | low | Low residual; minimal impact on adults after drying (UC IPM 2024) |
| Insecticidal soaps potassium salts of fatty acids | low | Contact only; no residual (UC IPM 2024) |
Commercial Availability
Aphidius colemani: 1–5 per 100 sq ft for prevention; up to 50 per 100 sq ft for established infestations (commercial guidance)
Introductions most effective at first sign of aphid colonies; mummy production visible within 10–14 days of release
Aphidius colemani parasitizes over 41 aphid host species and is the most widely used commercial aphid parasitoid. Mummy formation provides visible evidence of parasitism. Established populations can provide self-sustaining control in protected environments
Parasitized mummies and emerged adults are perishable; immediate deployment recommended. Short-term refrigeration at 40–50°F possible