Asking about 'function' is teleological and we cannot know unless animals could speak or God told us. But we can try to find out what advantage they confer by performing null hypothesis experiments or just simply guessing :)

There are articles

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187222.pdf

https://core.ac.uk/download/pdf/222896604.pdf

https://journals.biologists.com/Toolbox/DownloadCombinedArticleAndSupplmentPdf?resourceId=20845&multimediaId=1919757&pdfUrl=%2Fcob%2Fcontent_public%2Fjournal%2Fjeb%2F222%2F4%2F10.1242_jeb.190660%2F6%2Fjeb190660.pdf

Regards, Sergey

Dear Jakub Goczał . See the following useful RG links: Article Acoustic communication of the red‐haired bark beetle Hylurgu...

https://ir.canterbury.ac.nz/bitstream/handle/10092/17606/Bedoya_et_al_2019_hylurgus_UC.pdf?sequence=3

https://www.cabi.org/isc/datasheet/28843

Article Acoustics of the mountain pine beetle (Dendroctonus ponderos...

Kindly see also the following useful RG links: Article Acoustic communication in the pine engraver bark beetle: do ...

Article The most ancient bark beetle known: A new tribe, genus and s...

Thank you very much for the answers!

P. S. Dear Dr. Pegman, you should then inform the editor-in-chief of the "Functional Ecology" that the name of their journal is a heresy ;)

I suspect that elytral teeth could also be used as a defensive structures, or could play a role in a courtship or in a male-male competition, but I couldn't find any papers on this.

Teeth of elytra contain fungal spores in depressions, which infect undamaged tree wood.

extra-pair coitus in bark beetles has been investigated, in addition the following sources may help

Article Flight muscle changes in male pine engraver beetles during r...

Book The Evolution Of Insect Mating Systems

Book The Insect Societies

Females, and sometimes males, gnaw out a gallery in the wood for their offspring, give rise to mycelium. "Mushroom gardens" cover the walls of passages and are food for juveniles. What is most surprising, parents have special recessed pockets at the base of the legs and other places for transferring fungal spores to a new place. When the beetles leave their former mother passage, their pockets fill with spores of fungi useful to their offspring. This is one example of a symbiotic relationship between insect and fungi with closely intertwined life cycles. Beetles settle these mushrooms in their passages and temporary dwellings, creating the most favorable conditions for its development. In return, the mushrooms give part of themselves as food to the larvae. The formation of such mutually beneficial unions for the normal functioning of organisms is quite common in the living world. Such targeted actions and pre-prepared capabilities of the organism of representatives of these symbiotic species are carried out due to the interconnection of their genetic programs.

The family of bark beetles consists of several generations living together. In general, it is impossible to call bark beetles social insects, they do not pass by the formal criterion: truly social insects are those in which any group of individuals does not reproduce, sacrificing this function for the sake of the colony. Such a concept of sociality is useful, since it helps to delimit families of termites and ants from countless clusters of various kinds - in a place convenient for wintering, on a large amount of food ... But in this case, the introduced concept of sociality, perhaps, limits nature: bark beetles show us a type of social insects . Maybe this sociality does not reach that of an ant, but still, still ... At least none of the beetles came as close to the "social barrier" as bark beetles.

When searching for trees suitable for colonization, bark beetles are guided by special chemicals that a diseased tree emits. So, a bark beetle will sit on a completely healthy tree only in case of extreme hunger and the absence of weakened trees in the forest, and a healthy tree will resist this expansion for a long time, flooding bark beetles with resin when trying to break through under the bark.

Then, when the colony is already developed, at a long distance the connection between the sexes is still carried out due to pheromones - special substances that the female ready for mating emits. The male goes to the source of a wonderful aroma, and coming closer, begins courtship. If “chemistry” acts at a long distance, then at a close distance it is necessary to lure the female with songs. Males quietly “squeak” and “chirp”, charming females, confirming their belonging to this particular species of bark beetles. Female bark beetles also have a response “signal of consent”. The female ready for mating, having heard the signal of the male, whispers in response that she agrees.

In other genera of bark beetles, the female is the first to inhabit the tree, which gnaws the main passage under the bark, on the sides of which cozy niches are made where eggs are laid. Leaving the eggs, the larvae gnaw at the tree and make lateral passages. At the same time, the mother bark beetle often guards the larvae and cares for them. In some species, the mother delivers fresh food to the larvae and cleans the cradles. Throws out dust and garbage: works as a wheelbarrow. In the passages of bark beetles, fungi develop, which the bark beetles feed on. At the same time, they take care of their mushroom gardens, moisturizing them. Bark beetles carry fungi with them when settling new trees - sometimes the beetle has a special pocket for this, but many do without it: fungal spores are on the surface of the body of bark beetles, are abundant in their intestines, are excreted from them with excrement, etc.

Some bark beetles also have martial music. The male Ips pini, a close relative of the typographer, chirps menacingly if he encounters another male so intolerant of his presence at the appropriate time. Specifically, this jealous man cannot stand it when, near a certain minimal territory where he finds himself with his female, some other male impudently roams near his one-room mink.

Another type of signal is emitted by bark beetles so as not to get lost. They live in families, colonies, together eating the tree they like. The passages that are shared by all members of the colony need to be put in order, the mushroom gardens need minimal maintenance. Break away from your own - and you are dead, the tree will not tolerate you alone, and you will not feed yourself. That is why the bark beetles whistle, call out to each other, so that the family does not disperse in the dark corridors under the bark.

Andrew Paul McKenzie Pegman - you are right to some extent about the teleology. What most people have in mind in asking the question 'what is the function' of a structure they are really asking 'what is the purpose that it met to come into being', and of course many functional explanations are presented in terms of purpose (wings evolved to hunt, or to fly etc.). I think it is possible that one could ask about functional processes without the teleology by asking how does a particular structure mediate interaction of an organisms and the environment (blearing in mind that the two are intertwined and in some ways the organism 'constructs' is environment).

Sergey Viktorovich Pushkin's answer "parents have special recessed pockets at the base of the legs and other places for transferring fungal spores to a new place" is indeed a nice example of teleology - that the pockets are FOR transferring fungal spores (i.e. this is why they exist), rather than just they they are occupied by the fungus.

John Grehan Yes, but I’m not a fan of evolution since it really is just a theoretical, but non existent, ‘force’. And now you saying an organism constructs it’s own environment, but this is anthropomorphic, since it has no such ability. You’ve also got a spelling mistake

Andrew Paul McKenzie Pegman - 'blearing in mind' - ha ha. Everything is 'theoretical' in some way, if you agree with some philosophers. I don't worry about that. I was referring to construction in the sense that the 'environment' is not a separately existing entity in reference to any organism, rather a "co-construction'. This does not stop people from thinking of 'organisms' and 'environments' as separately existing entities.