Family common name: stem sawflies
Genus: Caenocephus Konow, 1896
The Cephidae are commonly known as stem sawflies because larvae feed and live within the stems of small herbaceous and woody plants. Many are considered pests, since this feeding behavior can damage or kill the plant host (Shanower and Hoelmer 2004).
Stem sawflies of the genus Caenocephus are generally black and slender, with slightly laterally compressed cylindrical bodies. The length of the abdomen is about equal or slightly longer than the head and thorax together, and females have a short ovipositor. Males and females sometimes have very different coloration, so it is more reliable to distinguish sex by the presence or absence of the ovipositor (Ries 1937). Caenocephus species are among the largest Cephidae and can be up to 20 mm in length (Smith 1986).
Caenocephus can be confused with other Cephidae. The most reliable character that distinguishes this genus from others in the family is the lack of preapical spurs on the hind tibiae. Additionally, this genus has an uncommon swelling at the base of the tarsal claws (Ries 1937).
In North America, the only confirmed host plant for Caenocephus aldrichi is Holodiscus discolor (ocean spray) (Hanson and Miller 1988). Middlekauff (1969) suggests a record from Conium maculatum (poison hemlock), but this host is unconfirmed.
Female Caenocephus oviposit into stems of shrubs (Middlekauff 1969). After hatching, larvae girdle the stem above by chewing in a line along the inner wall and interrupting the vascular system (Hanson and Miller 1988). The larvae feed on the vascular tissue of the plant, moving downwards towards the base (Shanower and Hoelmer 2004). Larvae are creamy white and grub-like in appearance. They lack abdominal prolegs, and thoracic legs are vestigial. Cephidae larvae possess a tubular dorsal horn on the posterior end of the body (Middlekauff 1969). As the larvae feed, they use this horn to pack frass in the gallery behind them. At the base of the branch, or after the tunnel reaches 1–5 cm, the larvae turn around and girdle the stem a second time. Once the plant above the girdle weakens and dies, it breaks off, leaving a stub topped with a frass plug, keeping the larva safe inside (Shanower and Hoelmer 2004, Hanson and Miller 1988).
Larvae generally undergo a period of diapause, either over winter or through a dry season, then pupate inside the stub. The adult chews or pushes its way out of the stub via the frass plug and emerges. Little is known about the adult behavior of this genus (Hanson and Miller 1988).
World: Caenocephus species are found throughout the Northern Hemisphere, with most species unique to their range. The genus occurs in North America, Europe, North Africa, and East and Southeast Asia (Taeger et al. 2010).
Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Caenocephus
Details about data used for maps can be found here.