A troublesome wasp

 

For the last month I have been finding specimens of a chalcid wasp by beating Lawson Cypress and other ornamental conifers. It is one of the Pteromalidae, a real ragbag of a family in desperate need of taxonomic revision - "a polyphyletic dumping ground of taxa that do not obviously fit within previously established families of Chalcidoidea" (Burks, R., et al (2022) From hell’s heart I stab at thee! A determined approach towards a monophyletic Pteromalidae and reclassification of Chalcidoidea (Hymenoptera). Journal of Hymenoptera Research, 94, 13-88) (glad it's not just me!).  I've had several goes at keying out these wasps, getting a different, moderately unsatisfactory answer each time. Along the way I have eliminated a few possibilities, and my most recent attempt strongly suggests that it is Macromesus amphiretus. It has all the characteristics of this species:

• Prepectus extremely small, hardly or not detectable. 
• Lower face with additional vertical groove parallel to genal groove. 
• Antennal formula of female 11173 (male 11172).
• Tarsi of female heteromerous, fore and hind tarsi five, mid tarsi four-segmented; first segment of mid tarsi in female very long.
• Both mandibles with three teeth.

All good - except for the fact that the hind margin of the propodeum does not match any of the three illustrations for this species I have been able to find. This would be a huge problem, were it not for the fact that each of the three illustrations is different! I am therefore inclined to call it Macromesus amphiretus, unless I can find an expert to tell me otherwise. 

Graham, MWR de V. (1969) The pteromalidae of north-western Europe (Hymenoptera, Chalcidoidea). Bull. Br. Mus. nat. Hist. (Ent.) Suppl. 16.

 

Boucek, Z. & Rasplus, J.Y. (1991) Illustrated key to west-paleartic genera. INRA Editions, série Techniques et Pratiques. ISBN 2-7380-0343-5.