Rhadinoceraea

Adults distinguished by thick antennae longer than head and thorax combined, shiny black coloration, and smoky wings. Larvae distinguished from caterpillars by having six pairs of prolegs rather than five; from other sawfly larvae by the combination of shiny black head, greenish-brown body with darkening in older individuals, and double rows of white dots around segments. Host plant association provides additional diagnostic information: R. micans on waterside irises, R. nodicornis on Veratrum species.

Associated with host plants in moist or waterside environments. R. micans occurs specifically where waterside irises grow; larvae do not attack irises on dry ground. R. nodicornis associated with Veratrum species.

Europe. R. micans recorded from Britain, France, Sweden, Finland, Denmark, Netherlands, Germany, Poland, Italy, Bulgaria, and Romania; absent from Spain, Sicily, Mediterranean islands, Greece, former Yugoslavia, and countries east of Poland. GBIF records indicate presence in Denmark, Norway, and Sweden.

Adults active in May. Larvae present from May through approximately July, after which they enter soil to pupate and overwinter. Adults emerge the following May.

Herbivorous; larvae feed on specific host plants. R. micans larvae feed on waterside irises including Iris pseudacorus, I. ensata, I. laevigata, I. spuria, and I. versicolor. R. nodicornis larvae feed exclusively on Veratrum species (Liliales: Melanthiaceae).

• Iris pseudacorus - larval hostprimary host; yellow flag iris
• Iris ensata - larval host
• Iris laevigata - larval host
• Iris spuria - larval host
• Iris versicolor - larval host
• Veratrum nigrum - larval hostR. nodicornis; source of steroid alkaloids
• Veratrum species - larval hostR. nodicornis; Liliales: Melanthiaceae

Eggs laid in May on host plant leaves in large flat placards; female inserts eggs into leaf blade near thickened middle, close to leaf base, up to 19 eggs per leaf. Larvae feed on leaves until approximately July, then crawl into ground, spin cocoons, and pupate. Overwinters as pupae. Adults emerge the following May. Univoltine.

Adults fly reluctantly and may feign death when touched. Larvae of R. nodicornis exhibit strict innate host specificity, accepting only Veratrum species regardless of early experience. R. micans larvae can occur in large aggregations.

Herbivore; some species sequester defensive compounds from host plants (steroid alkaloids in R. nodicornis from Veratrum; iridoid glycosides have been reported in related contexts). These compounds provide chemical defense against predators.

R. micans is a serious garden pest that can completely defoliate ornamental irises, particularly yellow iris (Iris pseudacorus) growing by water. Irises on dry ground are not attacked. The species is more frequently noticed as larvae than as adults.

• Other Tenthredinidae sawfliesLarvae distinguished by six pairs of prolegs (vs. five in caterpillars) and specific coloration patterns; adults distinguished by antennae longer than head and thorax combined.
• Other PhymatoceriniClose relatives share host associations with Liliales and Ranunculales; distinguished by specific host plant associations and, where known, chemical defense profiles.

• sawfly
• Tenthredinidae
• Phymatocerini
• herbivore
• chemical defense
• host specificity
• garden pest
• Europe

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Host specificity and host recognition in a chemically-defended herbivore, the tenthredinid sawfly Rhadinoceraea nodicornis
• Host specificity and host recognition in a chemically‐defended herbivore, the tenthredinid sawfly Rhadinoceraea nodicornis