Ichneumon Wasps
Ichneumonidae
parasitoid · caterpillar parasitoid · conservation
Last updated
Ichneumon wasps are a massive family of parasitoids with roughly 1,000 species in the Pacific Northwest alone. Females locate caterpillars, beetle larvae, and wood-boring insects using vibration detection and chemical cues, then deposit eggs inside or on the host. The developing larva feeds internally, eventually killing the host before pupating.
These wasps are exclusively conservation biocontrol agents since no species are commercially available. Their diversity means nearly every major caterpillar and beetle pest in the region has at least one ichneumonid parasitoid. Maintaining diverse plantings with nectar sources for adults and avoiding broad-spectrum insecticide applications are the primary conservation strategies.
Target Pests (11)
Quick Reference
Identification
Adult Description
Slender, elongated wasps, 10-40 mm body length. Long legs, long antennae (often as long as body), and narrow waist. Abdomen longer than head and thorax combined. Many species possess a conspicuous ovipositor extending beyond the abdomen tip, sometimes longer than the body itself, used to inject eggs into hosts or host substrate (wood, bark). Coloration varies: black, brown, orange, or banded. Distinguished from braconids by generally larger size and longer ovipositor (WSU HortSense; WSU HortSense Wasps).
Larval Description
Legless, maggot-like larvae developing internally within host body. Feed on host hemolymph and body fats, initially avoiding vital organs to keep host alive. Fully grown larva kills host and pupates either inside the host cadaver or in a silken cocoon nearby. Not visible externally until host death (general parasitoid biology).
Size Range
10-40 mm body length; ovipositor may add additional 20-50 mm (WSU HortSense Wasps)
Key Features
Slender build, very long antennae, prominent ovipositor in many species, narrow petiolar waist. Distinguished from braconids by larger average size and generally longer antennae.
Lifecycle & Phenology
Complete metamorphosis: egg, larval instars, pupa, adult. Females locate hosts using vibration detection, chemical cues, or visual search. Eggs are injected into or onto host bodies via the ovipositor. Larvae develop internally as endoparasitoids, feeding on host tissues while avoiding vital organs until the final instar, when the host is killed. Pupation occurs inside the host cadaver or in a silken cocoon spun nearby. Adults emerge and feed on nectar, plant sap, and occasionally honeydew. Most species are host-specific, attacking one or a few closely related host species. Multiple generations possible per year in mild PNW climate (WSU HortSense Wasps; Britannica).
| Generations per Year | [DATA GAP] - likely multiple in PNW growing season |
| Overwintering Stage | pupa |
| Egg Capacity | [DATA GAP] - females are synovigenic (emerge with some immature eggs, maturing additional eggs during adult life) |
| Larval Duration | [DATA GAP] - varies greatly by species and host |
| Development Duration | [DATA GAP] - species and temperature dependent |
| Adult Lifespan | [DATA GAP] |
| Active Months | April through October |
Habitat & Conservation
Adults require nectar sources for sustenance and egg maturation. Apiaceae and Lamiaceae are documented as optimal food plant families. Habitat structural complexity (hedgerows, diverse plantings) supports host-seeking behavior. Undisturbed areas for overwintering. Extremely sensitive to broad-spectrum insecticides (WSU HortSense; Jervis et al., 2003).
Nectar & Pollen Sources
Conservation Practices
- Permanent insectary plantings with Apiaceae and Lamiaceae for adult nectar provisionTiming: Established in fall or early springOnly 2 of 11 tested plant species (Aegopodium podagraria and Origanum vulgare) combined olfactory attractiveness with accessible nectar for ichneumonids; targeted plantings increase parasitism rates
Pesticide Sensitivity
| Product Class | Impact | Notes |
|---|---|---|
| Neonicotinoids imidacloprid, clothianidin, thiamethoxam | lethal | Systemic neonicotinoids are very toxic to parasitic wasps, especially when applied to flowering plants. Nectar-feeding adults directly exposed |
| Pyrethroids bifenthrin, permethrin, lambda-cyhalothrin | lethal | Broad-spectrum contact toxicity; residual activity on foliage kills host-seeking adults |
| Spinosad spinosad | moderate | Toxic on wet contact; reduced risk after drying |
| Horticultural oils mineral oil | low | Low residual; minimal impact on adults after drying |
| Insecticidal soaps potassium salts of fatty acids | low | Contact only; no residual |