Sphecophaga

Westwood, 1840

Species Guides

Sphecophaga vesparum

Sphecophaga is a of ichneumonid wasps specialized as ectoparasitoids of vespid . within this genus parasitize nests of social wasps, with larvae feeding externally on wasp pupae. The genus exhibits complex in forms and cocoon types, and has been widely introduced as a agent for Vespula wasp species. Two recognized species occur: S. orientalis parasitizing Vespa orientalis in the Mediterranean region, and S. vesparum with in Europe and North America targeting Vespula species.

Britishentomologyvolume3Plate198 by John Curtis
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Britishentomologyvolume3Plate198 (cropped) by John Curtis
. Used under a Public domain license.

Bulletin - United States National Museum (1962) (20322713419) by United States National Museum;
Smithsonian Institution;

United States. Dept. of the Interior. Used under a No restrictions license.

Pronunciation

How to pronounce Sphecophaga: //sfɛˈkɒfəɡə//

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Identification

are ichneumonid wasps with typical slender body form and long . Two adult female morphs occur in S. vesparum: large winged forms and small brachypterous (short-winged) forms. of S. vesparum can be distinguished by color characters with >98% for females and 100% for males; European S. v. vesparum and North American S. v. burra cannot be reliably separated by morphological characters alone. Three cocoon types are produced: soft white cocoons, weak-walled yellow cocoons, and rigid yellow/orange cocoons.

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Habitat

Found exclusively within nests of social vespid . In S. vesparum, this includes subterranean or aerial nests of Vespula vulgaris and Vespula germanica. In S. orientalis, occurs within nests of Vespa orientalis. The occupies the capped containing pupae.

Distribution

Native to Europe and North America (S. vesparum) and the Mediterranean region (S. orientalis in Israel). S. vesparum vesparum has established at limited sites in New Zealand (Pelorus Bridge, Marlborough; Ashley Forest, Canterbury). S. vesparum burra has not established in New Zealand despite extensive releases. GBIF records indicate presence in Denmark, Norway, and Sweden.

Seasonality

Winged of S. vesparum emerge from yellow cocoons after 1–4 years of dormancy, typically in spring or summer. Brachypterous females emerge from white cocoons within 13 days of oviposition. Multiple can occur within a single nest season.

Diet

Ectoparasitic larvae feed on pupae. In S. vesparum, larvae feed externally on newly pupated Vespula vulgaris and Vespula germanica. In S. orientalis, larvae feed on Vespa orientalis pupae.

Host Associations

Vespula vulgaris - Primary for S. vesparum vesparum
Vespula germanica - for S. vesparum vesparum and S. vesparum burra
Vespa orientalis - for S. orientalis; rate averages 23.48% of pupal in Israel

Life Cycle

Females oviposit into capped containing pupae. Larvae develop ectoparasitically on host pupae, then spin cocoons. Three cocoon types exist: white cocoons producing brachypterous females in ~13 days; weak-walled yellow cocoons producing winged females (and rarely males) in ~15 days; and rigid yellow/orange cocoons producing winged females after 1–4 years dormancy. The is facultatively deuterotokous, producing mostly parthenogenetic females with males rare and arising without .

Behavior

females preferentially oviposit on pupae that have most recently spun pupal caps. Winged adults may live up to 3 weeks. S. orientalis adults move freely within host colonies without aggression; this is achieved through chemical deception involving oleic acid (eliciting necrophoric ) and rose oxide (a repellent compound), rather than cuticular hydrocarbon mimicry. S. vesparum shows partial linear alkane matching of host hydrocarbons, likely through passive recycling of prey hydrocarbons.

Ecological Role

Specialized ectoparasitoid regulating of social vespid . Acts as a agent, though establishment success varies. In New Zealand, S. vesparum vesparum infests approximately 8.5% of nests annually at established sites, with no documented reduction in wasp nest attributable to presence.

Human Relevance

Introduced to New Zealand as a agent for Vespula vulgaris and Vespula germanica. S. vesparum vesparum was released from 1985–1987 and has established at limited sites. S. vesparum burra was released in 1979 and again from 1996–1998 but failed to establish. Recommended against further releases of S. v. vesparum due to limited efficacy; S. v. burra considered for potential re-release.

Similar Taxa

Other ichneumonid parasitoids of VespidaeSphecophaga is distinguished by its specialized polymorphic with three cocoon types and two female morphs, and its specific association with vespid nests rather than open-foraging .

More Details

Natural enemies

In the native range, S. vesparum has few documented enemies: Dimmockia incongrua, Melittobia acasta (Eulophidae), Dibrachys vesparum, D. boarmiae (Pteromalidae), and one unidentified chalcid. In New Zealand, only mice and a spider have been reported as field enemies; enemies appear to have minimal impact on .

Establishment factors

Successful invasion in New Zealand is associated with large founder numbers and high of nests. Only 20% of S. vesparum produce white or weak-walled yellow cocoons—the types that can reinfest the same nest—limiting within-colony spread and efficacy.

Subspecies

S. vesparum comprises two : S. v. vesparum (Europe) and S. v. burra (North America). A potential third strain from Israel may represent a distinct lineage but requires further study.