Päiväkirja-arkisto kohteelle syyskuu 2020

11. syyskuuta 2020

Xylobiops Identification

In North America, there are four species of Xylobiops. This journal entry will attempt to show how to distinguish them from one another. Two species have conspicuous hairs on the elytra. These are Xylobiops texanus (Horn) and Xylobiops sextuberculatus (LeConte). They can be distinguished from each other by the tubercles on the head. X. texanus has two in both sexes. X. sextuberculatus has 4 to 6 tubercles in the female and none in the male.

Xylobiops basilarus (Say) has no hair on the elytra and has a distinct separation between light (reddish) and dark colors. This gives it the common name red-shouldered bostrich. Xylobiops parilis (Lesne) also has no hair on the elytra.

The following is an illustration of something I've noticed but does not seem to be in the literature. It is useful for distinguishing the hairy group from the bald group when there is insufficient detail to see the hair.


The yellow lines are drawn at the base of the elytra and at the bend between the first set of spines. The green line is the distance between the yellow lines. The red line is the width of the insect. If the red line is longer than the green line, it is one of the hairy species. If the green line is longer than the red line, it is X. basilarus. I don't have data yet for X. parilis. So I don't know what category it fits in. If squares are drawn around the red and green lines, as illustrated, the difference is more obvious.

It looks like X. parilis can be distinguished by the fact the inner two pairs of tubercles on the elytra are blunt rather than sharp.

Following is a dichotomous key front in "A Revision of the North American Species of Beetles Belonging to the Family Bostrichidae", by W. S. Fisher, available online, digitized by Google.

  1. Dorsal surface of elytra (except apical declivity) without distinct pubescence, the yellow and black or brown areas conspicuously separated --- 2


    Dorsal surface of elytra (except along base) with distinct pubescence, the light and dark-brown areas not conspicuously separated --- 3

  2. Inner two pairs of tubercles along anterior margins of apical declivity of elytra acute or spinose at apices and coarsely punctured between tubercles, the surface of declivity coarsely, evenly punctured in fremale, with a few very coarse, deep punctures in male; front of head unarmed --- basilaris (Say)


    Inner two pairs of tubercles along anterior margins of apical declivity of elytra not spinose at apices, and not coarsely punctured between tubercles, the surface of declivity sparsely, finely, irregularly punctate in female, nearly impunctate in male; front of head with two media tubercles in both sexes --- parilis Lesne

  3. Apical declivity of elytra sparsely coarsely punctured; front of head usually with two media tubercles in both sexes --- texanus


    Apical declivity of elytra not, or very finely, punctured; front of head with four to six small tubercles in female, unarmed in the male --- sextuberculatus (LeConte)

Lähetetty 11. syyskuuta 2020 21:14 käyttäjältä victorengel victorengel | 0 kommenttia | Jätä kommentti