Tetragma

Tetragma gei Davis and Pellmyr

Adult Characteristics

Wing expanse 11-17 mm, with both sexes almost entirely pale ochreous or creamy white. The female possess a much elongated, telescoping abdomen used in reaching the deeply recessed ovaries of its host, Geum triflorum; the elongated seventh segment quickly loses its scales, and the exposed dark integument becomes another prominent feature of this species.

Comparison with similar species

The exceptionally telescoping abdomen of the female makes them unmistakable. The male is superficially similar to the somes co-occurring Greya subalba. It differs by having light tan or cream-colored forewings, whereas G. subalba has white forewings. The species is also usually found in immediate vicinity of its host, Geum triflorum, whereas G. subalba is found around members of Lomatium.

Host and larval feeding habits

Exclusively on Geum triflorum (mountain avens; Rosaceae). Early-instar larvae feed inside the developing seeds. An oviposition sequence, an egg, and an attacked Geum seed are shown in Davis et al. (1992)

Tetragma ovipositing into a Geum flower. Ovipositor reaches ovaries at the base of the flower (at red-tan transition on calyx).

Geographic Distribution

T. gei is so far only known from Washington, Idaho, Wyoming (Yellowstone), and South Dakota (Black Hills). The host plant is more widespread, however, and the moth may well occur over a larger geographic range.

Habitat

In herb-rich steppe and forest openings with Geum triflorum, often at 1000+ m elevation. The photograph below shows the type locality, where the moth coexists with Greya subalba.

Major reference:

Davis, D.R., O. Pellmyr & J.N. Thompson. 1992. Biology and systematics 
          of Greya Busck and Tetragma n. gen. (Lepidoptera: Prodoxidae). 
          Smiths. Contrib. Zool. 524:1-88.

Holotype in USNM.

About this page

Olle Pellmyr
E-mail: pellmyr@ctrvax.vanderbilt.edu.
Dept of Biology, Vanderbilt University, Box 1812-B Nashville, TN 37235, USA

Title Illustrations: Male (left) and female (right). U.S.A.: Washington: Asotin Co.