Aprosthema fusicorne - Vetch Twinhorn
One of three very similar Aprosthema species found in the British Isles. There are nine records recognised to date, including two in the last 30 years most recently in 2019. The pattern suggests a very rare and/or overlooked species of southern England, with a probable preference for wetter sites (Musgrove, 2022). The separation of the three species has been subject to much study and conjecture over the years. Aprosthema fusicorne is bivoltine and shows seasonal dimorphism adding to the confusion. Head shape differs in that the summer generation has a short head with strongly narrowing temples and longer flagellae, whereas the spring generation has a longer head with parallel or posteriorly broadening temples and shorter flagellae. Vikberg postulates that the head shape corresponds to the muscle requirements needed for emergence from the cocoon. The spring cocoon is weakly formed from soft plant material, whereas the summer cocoon is stronger and constructed underground.
Aprosthema fusicorne males can be distinguished from Aprosthema melanurum by the penis valve shape. Females of fusicorne have hind tibiae with minimal infuscate colouring and pale bases to hind tarsae 1-3.
Larvae feed on Viccia cracca L. and in full grown larvae the anal tergum has long, sharp medial projections. For key to species see Vikberg, 2004.
IUCN Status: Near Threatened
GB Rarity Status: Nationally Rare
Flight period: Bivoltine, May to August
Plant associations: Viccia cracca. Tufted Vetch (Vikberg, 2004)
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Liston A, Knight G, Sheppard D, Broad G, Livermore L (2014) Checklist of British and Irish Hymenoptera - Sawflies, ‘Symphyta’. Biodiversity Data Journal 2: e1168. https://doi.org/10.3897/BDJ.2.e1168
Lorenz, H. and Kraus M., 1957. Die Larvalsystematik der Blattwespen (Tenthredinoidea und Megalodontoidea). - Abhandlungen zur Larvalsystematik der Insekten No. 1. Berlin: Akadamie - Verlag
Musgrove, A.J. 2022. A review of the status of sawflies of Great Britain - Phase 1: families other than Tenthredinidae. Natural England, unpublished
Vikberg, V. (2004). Seasonal head dimorphism and taxonomy of some European species of Aprosthema (Hymenoptera: Symphyta: Argidae). Beiträge zur Entomologie = Contributions to Entomology, 54(1), 107-125