Pemphredon austriaca (Kohl, 1888) (Hymenoptera, Crabronidae) new to Suffolk
Early in 2022, this small solitary wasp was added to the British list as the result of rearing adults from Oak Marble galls, collected by Rosie Bleet in West Kent (Bleet & Early, 2022). Hymenopterists in mainland Europe have long known about this wasp’s use of these galls as nest locations, utilising the hollow within the woody gall once the original nest occupants (the cynipid wasp Andricus kollari) have vacated the gall. It is possible that this is the only nest location used by this Pemphredon, which immediately entangles its life history with that of the gall wasp and its dependence upon Turkey Oak (Quercus cerris) to complete its lifecycle. Despite this long-known association, it would appear that British entomologists have not been able to record this Pemphredon in Britain previously, suggesting that this might herald a new colonisation event rather than it being a long-overlooked native.
Having read about this discovery in Kent, the author resolved to try and find P. austriaca in Suffolk. To that end, on 10 February 2023, about 20 galls were collected
complicated by taxonomic uncertainty, name changes and misidentification. To confirm that the wasps were, indeed, P. austriaca, European identification guides were consulted and the author is grateful for the assistance of Tom Riffel in translating one of the main works from its original German.
Between 17 March and 7 May, 35 P. austriaca emerged from the Capel galls. David Basham also had some success, though with lower numbers. Three males emerged from the Christchurch Park galls in late May and early June and a single male from the Purdis Heath sample, also in late May.
Pemphredon wasps usually nest in hollow plant stems and galleries in dead and decaying wood. They are quite hard to find at the best of times, with specimens occasionally seen at the entrances to old beetle galleries in dead wood such as tree trunks that have lost their bark. To observe such wasps active at Oak Marble galls would require either extreme patience or good luck. It appears that the latter allowed Liz Huxley to photograph what is likely to be P. austriaca at galls in a nature reserve to the east of Colchester in north-east Essex. This, along with similar rearing success in Sussex this summer, suggests that this wasp may be quite widespread in south-east England.
Rearing from over-wintered galls represents the best and easiest way of recording this wasp. Members who are inspired to try this for themselves might do well to hold off collecting galls until early spring. This is because many over-wintering larvae and/ or pupae need to be exposed to winter frosts in order to trigger completion of their lifecycle once warm weather returns. Several other solitary bees and wasps opportunistically use old Marble galls, so there is an opportunity to record other species at the same time.
References
Bleet, R. & Early, J. (2022). Update on the genus Pemphredon (Hymenoptera: Pemphredonidae): P. austriaca: discovered as new to the British Isles in West Kent and P. enslini: confirmed as a resident species. BWARS newsletter Autumn 2022: 17–23.
Adrian Knowles
Jessups Cottage London Road
Capel St Mary Suffolk
IP9 2JR
hymenoptera@sns.org.uk