Family common name: cimbicid sawflies
Genus: Trichiosoma Leach, 1817
The family Cimbicidae is relatively uncommon and little-studied in North America. However, their large size and metallic reflections make the family somewhat conspicuous (Taeger 1998). Cimbicidae are robust, with the general shape of a bee, long hairs, and clubbed antennae (Smith 1993).
Trichiosoma are considered one of the “giant” sawflies because of their large size (~2.5 cm) compared to most other Symphyta. The combination of the large size and yellow- and black-striped coloration results in these sawflies appearing to mimic wasps from the family Vespidae. Males have notably enlarged mandibles, but because size and coloring are variable, sex is best determined by the presence or absence of an ovipositor (Smith 1993, Vilhelmsen 2019).
Trichiosoma can be confused with other Cimbicidae. In North America, they can be distinguished from Abia by their larger body size and the parallel inner eye margins, and from Cimbex by the presence of apical spur on the femora (Taeger et al. 1998). Trichiosoma are noticeably hairier than the other Cimbicidae (Goulet 1992).
In North America, documented hosts for Trichiosoma include the genera Alnus (alder), Betula (birch), Prunus (cherry), Ulmus (elm), Populus (poplar), Salix (willow), Corylus (hazel), Amelanchier (saskatoon), and Fraxinus (ash) (Wong 1954, Smith and Middlekauff 1987). There is evidence that Salix (willow) is the preferred host of Trichiosoma triangulum (Wong 1954).
Ovipositing females position themselves by clinging to the margin of a leaf, legs on either side. They steady the leaf margin using their ovipositor sheath, then insert the ovipositor saw between the cuticle and parenchyma along the upper surface. The saw moves back-and-forth to create a horizontal cavity. The egg is then deposited into this cavity (Chapman 1914).
Larval Trichiosoma are external defoliators. The larvae are caterpillar-like, usually green or gray with dark spots, and can be recognized by the one-segmented antennae and tarsal claws on each of the five-segmented thoracic legs (Smith and Middlekauff 1987).
Larvae react to potential predators by excreting a clear defensive liquid, a behavior called “reflex bleeding”, then fall to the ground, where they become difficult to see. At maturity, the larva will drop to the soil surface and build a cocoon in leaf litter. The prepupae overwinter in these cocoons. After pupation, the adult chews a circular hole in the cocoon and emerges (Harizanova et al. 2012, Smith and Middlekauff 1987).
Trichiosoma are univoltine (Smith and Middlekauff 1987), and adults fly in the spring (Burch 1973). Adults have been observed using their mandibles to girdle small twigs near the oviposition site (Eaton and Kaufman 2007).
World: This genus occurs throughout Asia, Europe, and North America (Taeger et al. 2010). Most collections have been made in Northern Europe, the Mediterranean region, and east to Siberia, Mongolia, Korea, and Japan (Sundukov and Lelej 2009).
Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Trichiosoma
Details about data used for maps can be found here.