Orchestes Alni (L.) Newly Discovered in North America (Coleoptera: Curculionidae)

Abstract

In spring 2003 some small reddish weevils were noticed feeding on the leaves of elm trees (Ulmus americanus L.; Ulmaceae) in Dekalb County, Illinois. These specimens were collected and sent to G.A.S for identification. Unable to assign a name to the species, G.A.S sent the specimens to R.S.A for examination. At the same time, S.J.K was receiving specimens of the same unknown Orchestes from elm in various nursery situations, and wrote to R.S.A seeking assistance with identification. With the assistance of C.W.O this weevil has now been identified as Orchestes alni (L.), despite its name, a European species associated with elms (Ulmus spp.). Orchestes alni is highly variable in color pattern and the color form represented in North America is that illustrated in Figs. 1 and 2. The presence of O. alni raises the number of species in Orchestes in North America to six (Anderson, 1989). O’Brien and Wibmer (1982:113, following previous authors) had erroneously reported O. alni as present in North America but this was based on the incorrect synonymy of O. alni with O. testaceus, an apparently native Holarctic species associated with Alnus and Betula (Betulaceae; Anderson, 1989). The correct generic placement of this species, and of the 5 previously known species in North America, is Orchestes Illiger 1798. Anderson (1989) and many other authors had placed the specie si nRhynchaenus, but the latter genus has now been restricted to a few related species feeding on Asteraceae in Europe, Japan and northern Africa (Alonso-Zarazaga and Lyal, 1999) and does not occur in North America. Adults of O. alni can be separated from other North American Orchestes by their characteristic color pattern and association with elms. The completely black Orchestes mixtus Blatchley is the only other North American species associated with elms (Anderson, 1989). Orchestes alni specimens have the head, rostrum, thoracic sterna and first three abdominal ventrites black, the dorsal surface red, the elytra with two oblique patches of black maculations, generally separated medially and forming three or four irregular areas of black (Figs. 1, 2). The weevils were first noticed in Dekalb County, Illinois in April 2003. Adults appear in the early spring, as the elm buds are beginning to expand. At this time they are both feeding on the leaf tissues and copulating. They can be active in very cool weather, which suggests that they overwinter as adults on or near the tree. Adults are very active jumpers. Adult feeding seems to concentrate on the lower sides of the leaf tissues. Feeding damage can be absolutely devastating to the appearance of the elm tree. No elm varieties are immune to the attack of the weevil, but ‘‘Homestead’’ elms (a hybrid elm resistant to Dutch Elm Disease) seem to be particularly susceptible. This damage is evidenced by many small round holes that are formed by feeding of adult weevils. Larvae, which mine in the elm leaves, are very small and creamy white with a light brown head capsule. The leaf mines are blotchy in appearance, more so than those of the elm leaf miner, Fenusa ulmi (Sundevall) (Hymenoptera; Tenthredinidae). Adult weevils are still actively feeding on elm during July; they have not been seen feeding on any other plants.