Psen longula TOURNIER 1899; Psen simplex TOURNIER 1899
There are approximately 100 species in this genus worldwide. Lomholdt (1984) states that there are only seven species in Europe, but Bitsch et al. (2001) list ten, although one of these, P. hidalgo, was only described in 1990. Three species have been recorded in Britain. Psenulus schencki is the least often recorded.
This is the most rare of the three British Psenulus species, being restricted largely to the south-east, with scattered records from the south Midlands and Dorset. Falk (1991) additionally lists Essex and Cambridgeshire.
It is found across central and northern Europe and northern Africa and has been recorded at 1600m above sea level in the Alps (Bitsch et al. 2001).
Shirt (1987) listed this species as being Rare (RDB3), but this was revised to Notable A (now Nationally Scarce Na) by Falk 1991. Only recorded for the first time in Britain in 1922, this wasp has increased its range but remains scarce and seemingly restricted to southern England. It is probably still expanding its range and is not thought to be under threat.
Recorded from a range of habitats where suitable scrub grows in warm, sunny locations.
Richards (1980) suggested that the activity of this species is more restricted than the other two Psenulus species, being confined to June and July, but Falk suggests a flight period of June to September. A single record gathered for this atlas project comes from May, recorded from Dulwich, London.
Danks (1971) notes the collection of adult Homopteran bugs within the family Psillidae (leafhoppers) (c.f. Psenulus concolor, which invariably takes nymphs).
Nests in cut stems of plants or small holes in decayed wood, especially old insect burrows. Danks (1971) noted numerous females constructing nests in the stems of butterfly-bush.The association with this plant and also elder is emphasised by Falk (1991).
P F Yeo (cited in Falk 1991) has observed this species at the flowers of hogweed.
No data available for British parasitoids, but Lomholdt (1984) mentions two non-British species that are known to attack P. schencki.
2009