Smell, scent, and chemical sensation, in humans and other animals (or plants), in particular insects, is an area of growing interest.
E.O. Wilson writes of a chemical grammar used by ants. As in many regions, we've seen an infestation of brown marmorated stinkbugs, whose alarm scent is spectacularly unpleasant. I'm curious about how insects perceive and react neurologically to chemicals.
This bit on human scent gives hints.
http://bigthink.com/videos/from-nose-to-brain-the-neurology-of-smell
In particular, I'm wondering if it's possible that chemicals act /directly/ with insect neurology to trigger responses -- that insects don't /respond to/ scent, so much as they are /directly driven by it/. Mind, this is uninformed speculation, but given the relative simplicity of insect neurological systems, strikes me as a shortcut which would leverage the perceptual system and behavioural outcomes in an efficient manner.
Related, the distributed brain of the octopus and RNA involvement.
2/
@dredmorbius while guessing, I expect that chemicals act more or less directly with insect neurology, because they breathe without a lung, i.e. their tracheae are distributed throughout their body.
@dredmorbius even plants "communicate" with chemical signals[1], e.g. to signal that some pest is intruding into their area, so yes, it is ok to think of the substances used as neurotransmitters, I'd say.
[1] There's even a research area called "plant neurobiology"
http://www.sciencedirect.com/science/article/pii/S1360138506001646
@cynix Right, and part of my thinking (hence: reference to other-than-animal systems).
@cynix The thought I'm working toward is that the chemicals used in insect communications are effectively exogenously-distributed neurotransmitters.