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Conflation of two white Geometrids

As I was trying to put IDs on some of my unidentified Geometrid images, I came across one species that I had overlooked but seems to be VERY similar to moths we have in Texas. The two species are:

Lobocleta peralbata, Hodges #7100, which is in the Sterrhinae;
and
Fragile White Carpet, Hydrelia albifera, Hodges #7423, a member of the Larentiinae subfamily.

The first of these is predominantly a southern species, ranging from AZ across to FL and the Carolinas; I have previously commented on the variability of Lobocleta peralbata across its range. By contrast, Hydrelia albifera is primarily found in the northern half of the continent, with reports as far south as AZ (?), TN, and Carolinas. I comment on this aspect later.

The superficial resemblance of the two moths is striking and I had tentatively changed the ID on a few of my images but then rethought the effort and began to study confidently-identified images of the two to tease them apart. Here I summarize what I can detect in images of the two. (I have no field experience with Hydrelia.) I offer a few comments here on some BG images that I think may be misplaced.

Both Species
Both species are about the same size with a wingspan of about 15-18mm. Lobocleta wingspans are given a slightly broader range of variation in the BG page for that species, but all measured specimens I've photographed are pretty close to the 15-18mm range in Central Texas. Both species rest with FWs widely spread, the leading margin of the wings either horizontal or pushed a little forward to create a wide angle.

In both species the white ground color of FW and HW is crossed by irregular narrow brown/tan lines, typically 3 on the FW and 2 on the HW. The details of these tan lines can be important for ID. All four wings have tiny black discal dots; rarely absent, the placement of the discal dots vis-a-vis the median tan line *may* be useful for ID.

Either species may have marginal black dots on the outer margin of the FW but these may be absent or worn off. The number and placement of the marginal black dots is sometimes useful.

Distinguishing Characters

Forewing Shape
The forewing of Lobocleta is consistently more triangular than Hydrelia; the costal margin of the latter species is typically curved through most of its length. Lobocleta has more of a tendency to hold the leading edge of the FWs horizontal which emphasizes the straight-edged nature of the wings. Hydrelia simply can't create that straight front-edge look due to the curvature of the FWs. I measured straight segments of the costal margin of the FW of each species (n=8 for each) and found that for Lobocleta, typically the middle 2/3 of the FW is very straight, often reaching nearly to the base (% straight avg. 68%, range 58-75%). In Hydrelia, the straightest measurable segment of the forewings averages barely 40% of the costal margin (range 29-50%). The hindwings of Hydrelia are proportionally deeper/longer, giving the species a much more "butterfly-like" outline. These wing shape differences are characterized in these images of
an Arizona Lobocleta: and
a New York Hydrelia:

Ground Color and Stippling
The white color of the wings of Lobocleta is opaque and may be tinted slightly yellow in some individuals.
The white wings of Hydrelia appear in some/most images to be slightly translucent with a rare tendency to show slightly creamy white.
A prominent character of nearly all Lobocleta peralbata is scattered dark (black or brown) stippling spread across both wings. This stippling is sometimes confined to just the forward 1/4 of the FW and it may be absent in worn specimens. This stippling is virtually never present in confirmed Hydrelia images (there being just a single example on BOLD which shows some black speckling). For this reason, I have a suspicion that this Arkansas image is misidentified and is probably L. peralbata:


Tan Lines on Forewings
There is a disconcerting amount of variability in the irregularity of the tan lines on Lobocleta, particularly in the PM line. In some individuals (particularly in the Southwest), the PM line is just slightly sinuous as in this AZ specimen:

but more often, the PM line is jagged and irregular and can be essentially identical to that of many Hydrelia which have a complete PM line:
vs.

More often than not, the PM tan line of Hydrelia is broken into a series of disconnected dots and dashes, particularly in more northern specimens:

I'm finding that some of the images of "Hydrelia albifera" which show a seemingly complete PM line are probably misidentified Lobocleta; see below. In many/most images of Hydrelia, the PM line, whether complete or broken, appears narrower than the Median line. In Lobocleta, these lines are equal in width and intensity. Most Hydrelia appear to have a partial and/or complete basal or post-basal tan arc (see previous image); this is absent in Lobocleta. A distinguishing character of some heavily-marked Hydrelia is a short tan bar connecting the AM and Median lines just below the costa (see the previous image). This bar, when present, appears to be diagnostic for Hydrelia.

Number and Position of Discal and Marginal Dots
The relative position of the Median line compared to the discal dots (which I assume are more fixed in position) is variable on both wings in both species. However, there is a tendency for the discal dots to be well-separated from the Median lines in most Lobocleta, particularly as one gets further west in the range as in this AZ specimen:
but there are exceptions as in the Central Texas image:
By contrast, there is a tendency for the discal dots to be adjacent or even imbedded in the Median line in most Hydrelia but this is quite variable as in these specimens from WI and NH:
vs.

At least half or more of all Lobocleta lack any dots or dashes on the FW outer margin. However, there are some heavily-marked individuals which show an evenly spaced series of narrow or bold vertical dashes along this margin as in these examples from West Texas and Florida:

Exceptionally, a few of the marginal dashes may be absent, yielding an "unbalanced" 4-and-1 or 5-and-1 sequence of dashes:


Typically in Hydrelia, when present, there may be only 1 to 3 marginal dots close to the apex of the FW:
Note the 5 or so dots descending from the apex of the FW on the heavily-marked individual from Canada, above.

Summary

While a few characters may occasionally be diagnostic in either Lobocleta peralbata or Hydrelia albifera, it is most easy to separate these two look-alikes by a combination of characters.

Lobocleta will have a much more triangular FW with a much straighter leading edge.
-- The wings are opaque white and often widely stippled black or brown.
-- The tan PM line may be sinuous or highly irregular but it is always complete and usually of equal width/darkness as the Median line.
-- There are no tan arcs or crosslines near the base of the FW (i.e., inside the AM line).
-- The discal dots are usually well-separated from the PM line (probably more applicable in the Southwest, less so from Texas eastward).
-- When present, dots on the FW outer margin usually form a complete set of narrow dashes or will occasionally have a gap between a set of 4 or 5 upper ones and a lower one.

Hydrelia albifera has a more rounded FW front margin and longer HW, giving it a more "butterfly-like" outline.
-- A tan PM line broken into a series of dots is diagnostic, but this line may be continuous; it is always very irregular.
-- The basal area of the FW typically has 1 or 2 partial or complete tan arcs or crosslines.
-- If present, a tan horizontal bar connecting the AM and Median lines below the costa is diagnostic.
-- Discal dots are most often contiguous to or even imbedded in the Median tan line, but may be separate in some populations.
-- When present, outer marginal dots on the FW typically number just 1 to 3 close to the apex. If more numerous (up to 5), the dots are on adjacent veins without a gap.

Redeterminations of Images
Much of the confusion/conflation of these two species appears to occur, as would be expected, in the zone of overlap (?) from OK and AR east to the Carolinas. Based on the discussions above, I will be adding comments to the following images for possible re-classification:

Four images from Sebastian Co., AR, all similar to this one, are likely to be Lobocleta peralbata. Note the FW shape and the lack of basal FW tan marks. If correct, this would leave AR without a BG image of Hydrelia albifera, consistent with the MPG map, above.

One image from Chester Co., TN--which is also posted on the MPG page for Hydrelia albifera has all of the characters of Lobocleta including correct wing shape, opaque white color, and the lack of basal FW tan lines, but the discal dots are contiguous with the Median lines. I judge this to be Lobocleta peralbata but it differs in ways that make it resemble Hydrelia more closely than individuals from the Southwest. Another image from Chester Co., TN, appears to be properly placed in Lobocleta.

The MPG map of Hydrelia albifera shows records from AZ and OK for which I have no basis to judge, but from all the above evidence, those might need to be re-examined. Similarly, an IA record of Lobocleta peralbata on MPG's map of that species would seem to be a geographical outlier, although the northward migration of moths in summer and fall might suggest a reason for such an occurrence.

Stippling and AM/Median Connecting Bar
I agree with the image from Chester Co., TN being Lobocleta and am changing it at MPG but in addition to discal dots contiguous with the Median lines, this seems to contradict your statement "If present, a tan horizontal bar connecting the AM and Median lines below the costa is diagnostic." You might want to edit that statement. Mike Quinn's Photo #314466 also has a connecting bar.

Also, BOLD has a specimen, sample DNA-ATBI-0225 which clearly barcodes as and looks like Hydrelia albifera but wings are stippled like Lobocleta. You may want to note that as well.

 
"Connecting Bar"
The connecting bar on Hydrelia is the line along the top of the cell, just below the costal margin, not the blurry connection of the AM and median lines in the middle of the wing shown on each of the cases you mention.
That single BOLD specimen with dark speckling negates my absolute statement but it is also an aberration compared to all other images. I'll modify the wording ever so slightly!

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