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

1. DISTRIBUTION

S. bifasciatus ^[1] is a common species that can be found throughout the Netherlands, with exception of the provinces Zeeland and Groningen where the species is rare ^[2,3].

2. BEHAVIOUR

2.1. ACTIVITY

The species is active from May until half September ^[2,3].

2.2. DEVELOPMENT

S. bifasciatus nests usually in hollow stemms, but may be found in walls (also of buildings) and dead wood ^[3]. She uses bee hotels as well and can be found in galls of the grass fly genus Lipara (CHLOROPIDAE) ^[3].

The female normally fills a nest cel with one prey, but sometimes two or more prey specimen are used when there is an abundance ^[4].

The female applies an adaptive strategy when building nests, so that the length of the cell is changed based on the diameter of the bore hole ^[5]. The resulting cel has effect on the sex of the wasp that develops in that longer cells will produce more and heavier females^[5]. There is no effect on males ^[5].
Also the larger the number of cells in a nesting cavity the less females will be produced. Older females will construct less cells and provide less provisions, and from those cell less females will develop ^[5].

BEE HOTEL

The wasp uses artificial nest help and has a preference for ^[5]:
– nest blocks located at 1 to 2 meters in height
– nest blocks with an orientation north or west (hypotheses), she uses nest blocks with southern or eastern orientation as well
– bore holes 3-4 mm in diameter

Section	Nest block
II	2, 8

3. PLANT RELATIONS

3.1. FOOD PLANTS

Adult S. bifasciatus wasps feed with necter and/or pollen. In literature the following plant species and groups are mentioned ^[5]:

Apicaceae

Pastinaca sativa ^[6]

3.2. PREY PLANTS

Research has shown that prey is found in different tree species and that S. bifasciatus is flexible in finding appropriate prey sources. The following trees have been identified:

Populus tremula^[4]

Salix sp.^[4,9]

Alnus incana^[4]

Garden species

As far as I know these trees are not in the vicinity of the garden, which may explain that I only found the species once so far.

4. PREY RELATIONS

The species is narrow oligophagous on beetlelarvae from the family of leaf beetles (CHRYSOMELIDAE) ^[3]. Literatuur mentions the following species that occur in the Netherlands:

CHRYSOMELINAE

– Plagiosterna aenea (Linaeidea aenea) ^[4]
– Phratora laticollis ^[4]
– Phratora vitellinae ^[4]
– Phratora vulgatissima ^[4,9]
– Plagiodera versicolora ^[4]

5. PARASITIC RELATIONS

The following nest parasites on S. bifasciates are mentioned in literature:

Cuckoo wasps (HYMENOPTERA, CHRYSIDIDAE)	– Chrysis angustula ^[3,10] – Chrysis ignita ^[3,8] – Chrysis fulgida ^[10] – Chrysis viridula (seen at nests) ^[3]
Chalcid wasps (CHALCIDOIDAE, EULOPHIDAE)	– Melittobia acasta ^[3]
Sluipwespen (*HYMENOPTERA, ICHNEUMONIDAE*)	Hoplocryptus – Hoplocryptus confector ^[10,11]

The following of these parasites have been observed in the garden:

Cuckoo wasps (HYMENOPTERA, *CHRYSIDIDAE*)	– Chrysis ignita
Sluipwespen (*HYMENOPTERA, ICHNEUMONIDAE*)	Hoplocryptus – Hoplocryptus confector ^[10,11]

6. IDENTIFICATION

Length males: 7 – 11 mm
Length females: 7 – 11 mm

Genus

Symmorphus can be recognized by the longitudinal groove on tergite 1 ^[7]. It also has a medial keel on tergite 1, a characteristic it shares with the genus Ancistrocerus.