Just how effective is using beetle aedeagi for precise identifications, and why?

Although I use beetle aedeagi frequently for somewhat basic identification, and sometimes exact IDs, I don’t always understand what I’m looking for to get the ID correct depending on what the situation (or proposed beetle) is.

How effective is using a photograph of a beetle’s aedeagus for identification compared to identifying it with the specimens in front of you. This seems like the better worded question I think.

I’m still getting a hang of the correct terms, and remembering how to use them.

Sorry, I wasn’t trying to publish this one just yet.

Okay, I think I finished.

How effective? Well, I have a revision of Harpalus* that I own for some reason and, unless someone has found other characters, it’s the only way to ID many of the species. It’s also why I have no interest in learning certain groups.

*Noonan 1991 - I’ll give it to anyone for the price of shipping.

edit: “no interest”

Basic identification should not require that. Too much work, simply.
Exact yes, but only for some tricky groups.

It varies. You would struggle to convince anyone that your Dryops were correctly identified if you didn’t have aedeagi. The Royal Ent. Soc. key to UK Stenus illustrates all their aedeagi but it isn’t always vital to have a male specimen, it is just a very useful confirmatory character. I can’t think of any but I am sure there are genera where the aedeagi are no help, or we haven’t yet spotted what are the critical differences. (Now I have thought of one - Anacaena are not always easy on external morphology, but the aedeagi are no help.)

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If you want to discover a new species, I suggest you think of a widespread and easily recognised species that you would normally identify in the field without looking at it critically, and start collecting it from different habitats, different geographical areas, and examining the aedeagi.

Hydrophilidae would be a good place to start. Several of the UK species have turned out to be species groups in recent years, with distinguishable genitalia but no external clues.

And it would probably be a good idea to keep a piece of each specimen in a form that can have its DNA extracted, because if you do think you have a new species, someone will want to do an DNA comparison.

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There are plenty of insect groups, mostly beetles admittedly, but not exclusively, where species are only identified by the genitalia. So, I think this question answers itself in those cases. If it’s a supportive character and not exclusive, then the answer relies on how reliable the visual morphology or other details are.

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