Two males discovered in Surrey in 2018. In both sexes the head is black with some yellow on the mandibles. The thorax is also black marked with yellow on the mesopleuron, mesepimeron and metapleuron. The female abdomen is red to burgundy with a broad, triangular, yellow membranous area in the cente of tergite 1 (red or orange in other members of the genus). The second, ninth and tenth (last) tergites in females are black. The male abdomen is black on the basal tergites and yellow to orange from tergite 4 to the apex. The legs are bright yellow in males, with grey coxae and the hind tarsi are grey to black. In females, the coxae are black and the legs brownish-yellow with the trochanter, the base of the femora and the first third of the tibia being pale or yellow.
Janus compressus larvae feed in the shoots of pears and on occasion apples, medlars, quince and chokeberry. The female makes incisions around the stem shoot causing wilt to occur. Larvae then feed in the wilted shoot from May to September. The shoot becomes blackened. Note that such damage can also be caused by shoot-cutting weevils.
Size: Female: 9 - 12mm, male: 6 - 9mm
Status: New arrival possibly spreading.
Flight period: May to June
Plant associations: Pyrus spp. but also Malus spp., Mespilus spp., Cydonia spp., and Aronia spp. (pears but also apples, medlars, quince and chokeberry)
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Halstead, A.J., 2018. Two stem-boring sawflies new to Britain, Janus compressus (Hym.: Cephidae) and Cladardis elongatula (Hym.: Tenthredinidae), British Journal of Entomology and Natural History, Vol 31(1), BENHS, Reading.
Validžić, T., Ivezić, M., Raspudić, E., Brmež, M. and Majić, I., 2013: Morfološke osobine kruškine ose srčikarice, Janus compressus Fabricius 1793. (Hymenoptera: Cephidae). Entomologica Croatica 17.