Official name:

Synonyms:

Gasteruption erythrostomum ^{[Soortenregister]}

Foenus erythrostomum (Dahlbom 1831)

see more on: www.gbif.org

Etymology:

erythrostomum

Greeks: red (erythro) Latin: mouth (stomum)

1. Distribution
2. Behaviour
3. Plant relations
4. Host relations
5. Parasitic relations
6. Identification

1. DISTRIBUTION

G. erythrostomum ^{[Soortenregister]} is found across the lower half of the Netherlands and is a rare species ^{[Waarneming.nl]}.
It is a permanent resident in the garden and can be found every year on the bee hotels in alternating numbers. Usually there are at least two females simultaneously active, males are less common and will occur with single individuals.
In 2020 I have recorded five simultaneously active females and two males. I think this is directly related to the large amount of Chelostoma rapunculi bees that were active in the garden, and especially in the bee hotels, in that year as well, see this post.

2. BEHAVIOUR

2.1. ACTIVITY

The species is active from May to August ^{[Waarneming.nl],[van Achterberg 2013]}.

Van Achterberg reports that the species is seldom active in May ^{[van Achterberg 2013]}, however in the garden it is active from the end of May.

2.2. DEVELOPMENT

Gasteruption wasps are parasites and infiltrate nests of bees, where the wasp larva will develop ^{[van Achterberg 2013]}.

The females are usually found on the bee hotels or hovering in front of sun warmed walls. The males fly in the vicinity of the females or elsewhere on sunny or less sunny spots. They are clearly capable of detecting the presence of a female, also when she’s no longer there. I’ve observed the female on the introduction picture of this article that rested on a branch of Verbena bonariensis. After she had already left for some time a male appeared that was clearly interested in that particular spot and kept hovering around and close to the branch but never landed.

The female has an ovipositor that she uses to deposit her eggs in the host nest.
The female use bee hotels as well. In order to find a suitable nest to infiltrate the female will hover in front of the nest site under construction and smell it out. When she has found a proper site she will land next to it and release her ovipositor out of the protective sheaths.
She will than stick the ovipositor down the nest shaft first followed by the abdomen. In my own observations the body followed next and she completely disappeared in nestsite, and have not observed that she only uses the ovipositor to penetrate a sealed nest. Normally she will keep the large part of her body outside the nest ^{[van Achterberg 2013]}.

Gasteruption erythrostomum ♀, Chelostoma rapunculi nest infiltrerend

The female in the movie below remained approximately 10 seconds in the nest before emerging again.

Directly after leaving the infiltrated bee nest she will clean and put the ovipositor back into the protective sheaths.

Gasteruption erythrostomum ♀, ovipositor schoonmakend

The pollen on the thorax of this female show that she has been in a bee nest.

3. PLANT RELATIONS

3.1. FOODPLANTS

The adult Gasteruption wasps feed with nectar and/or pollen and show a preference of plants from the following groups ^{[Jennings et al. 2004]}:

Apicaceae (Umbellifers)	Foeniculum – Foeniculum vulgare (Fennel)^{[eigen waarneming]}
Compositae (Composite family)
Crassulaceae (Stonecrop family)	Sedum – Sedum album (White stonecrop)^{[eigen waarneming]}
Euphorbiaceae (Spurge family)

Table 3-1: Food plants in the Netherlands

4. HOST RELATIONS

Gasteruption are parasitic wasps on bees ^{[van Achterberg 2013],[Parslow et al. 2020]}. There are no clear relations known with wasps ^{[Parslow et al. 2020]}.
The larvae can start as egg predator or as ectoparasitoid on the larva, and continue as cleptoparasitoid on the remaining food supply. When that does not provide enough food it will continue to parasitize the next cell ^{[van Achterberg 2013]}.

G. erythrostomum parasitizes on bees from the subfamily Megachilinae ^{[van Achterberg 2013],[Parslow et al. 2020]}, with a preference for Chelostoma.
The following hosts sited in literature occur in the Netherlands ^{[Parslow et al. 2020]}:

Colletidae *(Bijen – Anthophila)*	Chelostoma preference ^{[van Achterberg 2013]} – C. campanularum ^{[Parslow et al. 2020]} – C. rapunculi ^{[Parslow et al. 2020],[eigen waarneming]} Megachile ^{[van Achterberg 2013]} Osmia ^{[van Achterberg 2013]} Heriades ^{[van Achterberg 2013]}
Megachilidae *(Bijen – Anthophila)*	Hylaeus – H. communis ^{[Parslow et al. 2020]} – H. hyalinatus ^{[Parslow et al. 2020]} – H. pectoralis ^{[Parslow et al. 2020]} – H. punctatus ^{[Parslow et al. 2020]}

Table 4-1: Host species in the Netherlands

Host species outside the Netherlands:

–

Table 4-2: Host species outside the Netherlands

Chelostoma rapunculi bees nest within the present bee hotels in the garden. I have twice observed directly how a female G. erythrostomum infiltrated na C. rapunculi nest with free ovipositor (see also chapter 3), which is a possible indication that an egg has been deposited ^{[van Achterberg 2013]}.

5. PARASITIC RELATIONS

The following species and groups occurring in the Netherlands ^{[Soortenregister]} are mentioned in literature:

–

Table 5-1: Parasitic species in the Netherlands

Parasitaire soorten buiten Nederland:

–

Table 5-2: Parasitic species outside the Netherlands

6. IDENTIFICATION

Length males: – mm
Length females: – mm

Genus

Genus

Gasteruptiidae are easy to recognize by the elongated neck, the swollen hind tibia and the highly attached slender abdomen ^{[van Achterberg 2013]}.

Only the Gasteruptiidae group have the swollen hind tibia the function of which is unclear. Research has shown the tibia is filled with fat. This may have a function to increase sensitivity to detect prey in potential nesting sites, or is used to increase balance during flight and hovering. The latter aspect has been tested and shown that wasps with the tibia removed have more difficulty to make turns ^{[Mikó et al. 2019]}.

1. Antenna: with 14 segments ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♀︎, antenna female with 14 segments

2. Ovipositor: black with the white tip shorter than the hind basitarsus ^{[van Achterberg 2013]}
3. Ovipositor: length 0,6-0,8x length abdomen ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♀︎, white tip ovipositor sheaths shorter than basitarsus

*Gasteruption erythrostomum* ♀︎, ovipositor sheaths black with white tip

4. Hypopygidium: with deep incision ^{[van Achterberg 2013]}The hypopygidium is located at the underside of the abdomen near the tip^.

*Gasteruption erythrostomum* ♀︎, hypopygidium deep

5. Hindleg: tibia relatively wide with ivory colouring at the base ^{[van Achterberg 2013]}

Gasteruption erythrostomum ♀︎, hindtibia base with ivory color

6. Antesternale carina: narrow ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♀︎, antesternal carina narrow

7. Occipitale carina: relatively wide ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♀︎, occipital carina broad

8. Eyes: without hairs ^{[van Achterberg 2013]}
9. Mandible: usually orange or yellow-brown ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♀︎, eyes without hairs, mandibel orange or yellowbrown

1. Antenna: 13 antennal segments ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♂︎, 13 antennal segments

2. Hindleg: basitarsus relatively long ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♂︎, Hindleg metatarsus relatively long

3. Hindleg: tibia and tarsus more or less black or darkbrown ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♂︎, hindleg tibia and tarsus usually black or darkbrown

4. Antesternale carina (S): not lamelliform and narrow, resembles the prepectal carina (P)

Gasteruption erythrostomum ♂︎, antesternale carina (S) not lamelliform and narrow, resembles prepectale carina (P)

5. Mesoscutum (M): regularly sculpted ^{[van Achterberg 2013]}
6. Mesoscutum (M): structure contrasts with sidelobe (S), sidelobe rugose ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♂︎, structure Mesoscutum (M) contrasts with sidelobe (S), sidelobe rugose

*Gasteruption erythrostomum* ♂︎, side lobe rugose

7. Head: relatively wide ^{[van Achterberg 2013]}

*Gasteruption erythrostomum* ♂︎, head relatively wide

8. Occipital carina: well developed: wide and lamelliform ^{[van Achterberg 2013]}
9. Occipital carina: dark in color ^{[van Achterberg 2013]}10. Occipital carina: 0,3-0,5x width diameter hind ocellus^{[van Achterberg 2013]}