The Choristoneura rosaceana Confusion (credit: Jason Dombroskie)
Early on in my iNat moth experience, I realized the identifications of Jason Dombroskie are invaluable. When he says something isn't something, I don't question it--until today. I thought I had the associated observation right at Choristoneura rosaceana, but then I spent too long looking at it, and went for C. parallela owing to a lack of flare near the apex of the costal margin. Of course, Mr. Dombroskie corrected my error...but why? I asked and he, quite courteously, answered:
"I get that question a lot so I did a short write up a while back:
"Today I was asked how to separate species that look similar to Choristoneura rosaceana and thought I'd share my response here since it is commonly collected and frequently misIDed. The short answer is assume everything is C. rosaceana unless you have reason to believe otherwise. The longer answer is below and basically outlines my thought process. Note this doesn't always work and I still have a pile of specimens that I haven't put a name on yet. So treat this advice as tentative.
"Archips purpurana males with stout FW with an angular costal margin and females with an exaggerated costal sinuosity.
C. fractivittana is pretty distinctive by smooth FW pattern in both sexes and slender costal fold in the male.
C. albaniana have a far northern / high elevation distribution. FW usually finely strigulated, can sometimes have a greyish wash or all grey. HW white.
Male C. rosaceana almost always have a rudimentary triangular costal fold (all species below lack a costal fold). Highly variable FW pattern. When in doubt, brushing the tip of the abdomen will show a bulbous uncus. Widespread and abundant.
C. obsoletana males usually have the median band obsolete in the middle of the FW. Common in FL, rare northwards to KS, IL, & MA. Uncus slender, sacculus more-or-less smooth and nearly reaches end of valve.
C. parallela males vary a bit in FW pattern, but usually pale brown - straw. Widespread in east, rare n of MO - OH - NY. Uncus slender, sacculus is roughly 3/4 length of the valve and with a variably expressed tooth near middle.
C. zapulata males usually have a pale straw FW. Widespread in west, in east restricted to Great Lakes dunes and a few populations in NB & QC. Brushing will show a variably broad uncus, sometimes almost similar to C. rosaceana.
Female C. rosaceana FW highly variable, costal margin usually sinuous, though not as exaggerated as A. purpurana. HW usually half orange half grey. Sterigma sclerotized and cup-shaped (largely membranous with a colliculum in next three species).
Female C. parallela FW with straight to at most subtly undulating costal margin, usually orange and with a well defined median band. HW half orange half grey.
Female C. obsoletana FW with straight costal margin, often orange and usually with the median band broadly interrupted in middle. HW yellow.
Female C. zapulata FW with straight costal margin, straw coloured. HW half whitish half grey."
That's a lot to digest, especially when you're not quite as fluent in moth morphology as the experts. Understanding these descriptions usually involves reading with my guides in hand--two or three or times over. BUT it's getting easier as time goes by.
Many thanks, sir!
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