Diprion similis - Cryptic Pine Combhorn
Unlike many pine-feeding species, most records of Diprion similis have been from southern Britain. However, a male was caught in native pinewood at Beinn Eighe, Scotland in 1988, suggesting that it too may have a native component to its population. Other records are from Cheshire southwards, although a larva was photographed in Northumberland in 2021 (Musgrove, 2022).
The two Diprion species can only reliably be distinguished by the saw teeth and the penis valve since the external features of both are variable. Both species are yellowish with various degrees of black on the head, mesonotum, mesosternum and tergites 3 to 6. Diprion similis is the rarer of the two species and has a more southerly distribution. Females have saws with regularly spaced and evenly sized teeth. The penis valve is only more deeply sinuate on the serrated edge.
Larvae of Diprion similis initially feed gregariously on pines dispersing after the third instar. Eggs are laid in rows in a slit in mature pine needles and larvae prefer to feed on the pine needles of previous years. Female larvae have six instars and males only five. First generation larvae form cocoons on pine needles whilst second generation larvae may form cocoons in the leaf litter. Adults may emerge from overwintered cocoons over a long period from April to August and late emerging individuals may possibly coincide with the emergence of second generation adults.
Size: 7 - 10mm
GB IUCN Status: Least Concern
GB Rarity Status: Nationally Scarce
Distribution: England, Scotland, Wales
Flight period: Univoltine May to July, or bivoltine May to July, July to August in warmer years
Plant associations: Pinus spp. (pines) including Pinus strobus (Weymouth Pine) and Pinus sylvestris (Scots Pine). Five-needled pines (e.g. strobus) are preferred.
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Coppel, H.C., Mertins, J.W. and Harris, J.W.E., 1974. introduced pine sawfly, Diprion similes (Hartig)(Hymenoptera: Diprionidae). a review with emphasis on studies in Wisconsin. Res Bull Res Div Coll Agric Life Sci Univ Wis.
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
Musgrove, A.J. 2022. A review of the status of sawflies of Great Britain - Phase 1: families other than Tenthredinidae. Natural England, unpublished