Acroricnus stylator (Thunberg, 1824)

Verheyde, Fons, Hoekstra, Paul, Libert, Pierre-Nicolas, Meijer, Hilco, Ketelaere, Augustijn De, Vandaudenard, Thibaud, Belgers, Dick & Brosens, Edwin, 1880, Two hundred and five ichneumonid wasps reported for the first time in Belgium and the Netherlands (Hymenoptera: Ichneumonidae), Belgian Journal of Entomology 122, pp. 1-142 : 52

Acroricnus stylator (Thunberg, 1824)

Acroricnus stylator can be easily recognised within the cryptine wasps on the basis of macroscopic features, but strong characteristics are the position of the petiole (spiracle before the middle) and the last segment of the hind tarsus with a group of large midventral bristles ( TOWNES, 1970a).

It is an impressive ichneumonid wasp with a long ovipositor and slender metasoma. Especially the colouration of the hind legs and antennae is quite unique, although there is variation to some extent. The trochanters are black, the femora are orange to red, the tibiae are orange to red with a broad black band apically (approximately 0.4× the total length) and have distinct spurs. Some male specimens also have a black apical band on the femora. The hind tarsi are white to creamy yellow. The antennae always have a thin white ring medio-ventrally, covering at least two flagellomeres. The females sometimes have their flagellomeres orange basally and black apically. The males have a yellow clypeus. Most of the field observations were made in the summer (July–August) and came from moorlands where high temperatures are reached. Animals were often spotted feeding on umbellifers. However, there are also some observations from May (data from waarneming.nl), suggesting the species is bivoltine, sharing this aspect with the closely related and in the Low Countries unreported Acroricnus seductor (Scopoli, 1786) ( POLIDORI et al., 2011) . Hosts are eumenine wasps ( Hymenoptera : Apocrita : Vespidae ), with at least Eumenes coarctatus (Linnaeus, 1758) as a certain report ( MARCELIS, 2008). Despite the species’ grandeur and distinct appearance, distribution maps (e.g. FAUNA EUROPAEA) clearly suggest it has been overlooked in Belgium.

First report for Belgium; confirmed in the Netherlands.

MATERIAL EXAMINED:

BELGIUM: • 1 ♂; Mol , Buitengoor (AN); 51°13’03”N 5°10’51”E; 30/vii/2020; J. Thora leg.; field observation; F. Verheyde det. (ObsID: 197557119) .

THE NETHERLANDS: • 1 ♀; Fochteloërveen (FR); 52°59’59”N 6°22’56”E; 4/viii/2009, F. Visscher leg.; field observation; F. Verheyde det. (ObsID: 44091854) . • 1 ♂; Elsendorp (NB); 51°34’18”N 5°47’21”E; 22/v/2013; A. Jacobs leg.; reared ex Eumenes sp. (dome); F. Verheyde det. (ObsID: 76297402) . • 1 ♂; Wellerlooi , Uiterwaarden (LIN); 51°30’50”N 6°09’32”E; 29/vii/2013; L. Troisfontaine leg.; field observation; F. Verheyde det. (ObsID: 77985777) . • 1 ♂; Ospel , Groote Peel (LIN); 51°19’37”N 5°48’05”E; 8/viii/2015; P. Smeets leg.; field observation; F. Verheyde det. (ObsID: 105231350) . • 1 ♀; Sint-Anthonis (NB); 51°37’17”N 5°50’19”E; 14/viii/2015; A. Jacobs leg.; field observation on dome of Eumenes coarctatus (Linnaeus, 1758) ; F. Verheyde det. (ObsID: 105568900) .