Family common name: common sawflies
Genus: Rhadinoceraea Konow, 1886
Subgenera: Rhadinoceraea, Veratra
The Tenthredinidae are the most species-rich family and are found throughout the world, in all continents but Antarctica. They are known as the “common sawflies.” They can generally be recognized by a cylindrical body and long, segmented antennae. Otherwise, they come in a variety of colors, sizes, and forms (Goulet 1992).
Sawflies in the subfamily Blennocampinae have a diverse set of life histories and habits. Many species are restricted to subtropical and tropical regions, but the genus is still fairly species-rich in North America. Blennocampinae includes many sawflies that feed on ornamental and forestry crops. This subfamily can be recognized by wing venation and bidentate mandibles (Smith 1969d).
Rhadinoceraea are medium-sized, about 6–8 mm in length, and almost entirely black with darkened wings (Smith 1969d).
A key to North American species is included in Smith 1969d.
Rhadinoceraea can be confused with similar species in the subfamily Blennocampinae. It can be distinguished from most other genera by the developed pulvilli on basal tarsomeres and the furcate apex to veins 2A and 3A of fore wing. Rhadinoceraea can be distinguished from similar species in Phymatocera and Paracharactus by the short mesoscutellar appendage (Smith 1969d).
Sawflies of this genus are generally not considered pests. The poisonous plants that serve as their host are often a nuisance to livestock farmers, and thus Rhadinoceraea has potential use as biocontrol for these dangerous plants. Rhadinoceraea nodicornis, for example, is monophagous in Europe on Veratrum album (white false hellebore) and is being considered as a biocontrol agent due to this specificity (Schaffner et al. 2001).
In North America, Rhadinoceraea feeds on Calochortus, Stenanthium densum (crowpoison), Veratrum viride (green false hellebore), Veratrum californicum (California false hellebore), and other species of Veratrum (false hellebore) (Smith 1969d, Smith and McDearman 1990, Goulet 1992).
Female R. aldrichi oviposit into small chambers they create on the underside of the leaves in short rows parallel to the main vein. After hatching, larvae feed on the leaf tissue leaving small, irregular holes (Smith 1969d).
Two species, R. zigadenusae and R. sodsensis, share an uncommon larval habit of feeding on flower parts. Females deposit eggs singly into the stalks of flower inflorescences. Young larvae burrow into the flower buds to feed on the immature stigma and stamen, and as they develop move to feeding on mature flowers and fruits. These species are univoltine (Smith and McDearman 1990, Smith and Barrows 1995).
Several of the host plants of Rhadinoceraea are toxic. European species R. nodicornis is documented sequestering alkaloids from its host plant into the hemolymph. Combined with the larval habit of “easy-bleeding,” a behavior that is also present in R. micans, the toxic hemolymph is used as a predation defense (Barker et al. 2002, Voigt et al. 2011). These accounts suggest that these defensive behaviors may be shared by North American species.
World: This genus is known from North America, Central and Eastern Europe, through Russia, and in China (Taeger et al. 2018).
North America: Rhadinoceraea is a mostly western genus. Species of the subgenus Rhadinoceraea occur in southern California and in Utah. The majority of the subgenus Veratra occurs throughout the Pacific coast from California to Alaska and east into Idaho and Alberta. Some species have eastern ranges: R. nubilipennis occurs east of the Appalachian mountains from North Carolina north into Quebec (Smith 1969d), and R. zigadenusae and R. sodsensis occur south in West Virginia, North Carolina, Mississippi, and Alabama (Smith and McDearman 1990, Smith and Barrows 1995).
Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Rhadinoceraea
Details about data used for maps can be found here.