Broad-headed bugs of the genus Alydus

Fracker (1918) discusses how difficult it is to identify many species of Alydus (except pilosulus) without examination of genitalia. "Owing to numerous variations, especially in A. eurinus and A. conspersus, the present writer has been compelled to rely on genitalia for the separation of these two species and their relatives." More recently, Schaefer and Shaffner (1994) provide no obvious morphological characters to distinguish eurinus, calcaratus, and tomentosus.

Here's what I've gleaned so far from the available literature:

• Alydus pilosulus: (eastern half of U.S. and Quebec): Humeral angles of pronotum are sharply acute and the antero-lateral margins of the prothorax are usually pale.
• A. scutellatus (Rocky Mountains): posterior femora with pale annulus near apex (others members of the genus lack this annulus).
• A. conspersus (Canada, across northern U.S., south to Arizona along Rocky Mountains): membrane often spotted, body without long, erect hairs.

When the above-mentioned characters are visible, those three species are fairly easily identifiable. The greater challenge lies with the following three species. How to distinguish them in areas of sympatry without genitalia? Evidently, the variation within species makes this task impossible.

• A. eurinus (U.S. and Canada): pronotum usually black, membrane without spots.
• A. calcaratus (western Canada, Quebec, Minnesota, Alaska, NW U.S. and south along Rocky Mountains to SW U.S.): body dark brown (fuscous) to black.
• A. tomentosus (SW U.S. perhaps north to S. Dakota).

A. pluto was synonomyzed with A. calcaratus by Schaefer and Shaffner (1994).

Available literature describing characteristics:
Fracker, S. B. (1918). The Alydinae of the United States. Annals of the Entomological Society of America, 11(3), 255-280.
Schaefer, C. W., & Schaffner, J. C. (1994). Alydus calcaratus in North America (Hemiptera: Alydidae). Proceedings of the Entomological Society of Washington, 96(2), 314-317.
Swanson, D. R. (2011). A synopsis of the Coreoidea (Heteroptera) of Michigan. The Great Lakes Entomologist, 44(3 & 4), 4.

Posted on 23 November, 2020 22:46 by pfau_tarleton