I'm curious to know why specimens of Trimerotropis from west Texas, Nebraska and Colorado, currently marked as T. saxatilis on BugGuide, aren't being called T. pallidipennis? While the two are similar, and there are integrades where the two co-occur, T. saxatilis is typically smaller, darker, with blackish, whitish and green markings, strongly resembling the lichen encrusted rocks on which they exist. Following Otte, Trimerotropis saxatilis confined almost entirely to the Ozark-Shawnee Hills region and scattered populations on high-altitude glades and rock outcrops of the central and southern Appalachians. Those larger, grayish specimens from further west, with the broad pale band(s) between the two-three dark bands on the forewing, appear to be typical pallidipennis.

This particular specimen is perhaps one of the more debatable posted here on BugGuide, but I can't examine it to be certain. Most posts are quite certainly correct.

I have never found any indication that the two species intergrade, nor have I personally ever seen what would appear to be a hybrid (though that doesn't mean that it can't happen - probably only very rarely). In fact when found in the same area they are clearly distinct in both morphology and behavior (they do not even sound the same), and are easy to distinguish from one-another. It has become clear in recent decades that the two have been badly confused and the distribution of T. saxatillis greatly underestimated (including by Otte), but this is not widely expressed in literature on Acrididae yet (there has been very little related literature in recent decades). Otte didn't recognize that there were two things occurring over a large area, but there are. He may have included some northern Great Plains material under his expansive concept of T. diversellus though.

The coloring of T. saxatilis depends largely upon which substrate it occurs. It is possible that more than one taxon are involved, but they are clearly not T. pallidipennis. I'll have to look and see if I'm am remembering correctly, but I think there is one published phylogenitic study including T. saxatilis specimens from a few assorted localities (including Colorado) and they all grouped together, distinct from T. pallidipennis (however, I might be remembering something that was never published).

On the other hand, it is quite probable that T. diversellus is connected with and part of T. saxatilis, as there is no clear distinction between it and T. saxatilis from limestone outcrops on the Great Plains. Otte's definition of T. diversellus includes at least three species (perhaps four if some material of T. salina was also included), but only the material from near Yellowstone was really T. diversellus, while at least two unnamed species from further west are involved (and probably a lot of material of true T. pallidipennis as well?).

The true distribution of T. saxatilis is from the Peidmont in North Carolina and Georgia to the east base of the Rockies in New Mexico, Colorado, and Wyoming, and perhaps Montana. West of the Mississippi it has been collected (always associated closely with rock exposures) from New Mexico, Colorado, Wyoming, South Dakota, Nebraska, Kansas, Oklahoma, Texas, Arkansas, Missouri, and I suspect it will turn up in Iowa (though perhaps there is not enough suitable habitat there?), and in eastern Montana, and there may be material (I haven't examined it) collected from Alberta and Saskatchewan.

There is a comparison photo here, but it would be better if there were series compared, in which case the difference would be even more obvious:

https://bugguide.net/node/view/216657

In fact, if you look at the records here, you'll see that there are many records for T. pallidipennis, and only a select few of T. saxatilis. Some may be indeed be incorrect in both directions, but I think it is very few, if any.

Wherever found, T. saxatilis matches it's substrate. The covering of lichens and mosses seen on rock outcroppings in the east are mostly missing, or at least less prominent on drier similar outcroppings in the west, and so an insect of the striking, often green and black coloring seen someplace like Missouri, Tennessee, North Carolina, or Georgia would most likely be very much at a disadvantage in the west. Across much of the mid section of the country these insects are found associated with limestone, and these look very different. They look different on pink granite in Colorado or Texas as well. Regardless, they are morphologically and behaviorally the same. And, of course it is also possible that there is some ongoing gene exchange that could affect appearance some between T. pallidipennis & T. saxatilis where they do overlap distributions (west from western Arkansas and eastern Kansas and Nebraska), but I have seen no evidence of it. [They are clearly very closely related.] A place to look for such might be in eastern Montana, where there are some interesting looking but unstudied populations.

Oh - almost forgot - size between eastern and western populations isn't that different. They do tend to be larger in Texas, but isn't everything? Seriously, there is a trend to be larger southward than northward on the Great Plains, but that is typical for most species.

And, if you want to find these things on the Great Plains, you really have to search them out - they are very restricted to particular localized habitats, even if it is a wide-ranging species. As a kid, I collected for many years in northeastern Colorado before I realized that they were there, but I saw T. pallidipennis all the time as something of a "weed" to be ignored (one of several reasons why everyone tends to miss finding T. saxatilis.

It is worth noting that many of the same comments can be applied to T. salina, which is also extremely habitat specific, and which is very closely related to both T. saxatilis and T. pallidipennis.

comment was duplicated in editing.