Just did a few runs with the insect glaive... a few questions:
Whenever I press R and release which shoots, that's just to mark a target, right?
When I send an insect, does it do damage, or just harvest powers?
Once an insect returns, I'm assuming my melee attacks are what are being powered up?
Is there any reason to recall an insect, or should I just let it come back to me on it's own? If I recall an insect early, do I get less powers from the monster?
Yes, it marks the target. You can also mark by hitting R+A during a combo.
The insect does damage. You can charge it by holding Y (or is it X... wherever Triangle would be on PS). Its damage depends on its stats, which you increase with nectar.
Red juice powers up your attacks and adds extra swings. I would recommend you ALWAYS grab red essence before attacking. Try and get red and white, as it extends the effect and makes you even stronger. If possible, get red, white, and orange for an even bigger boost and longer duration. You will also get a defense boost and earplugs.
Practice harvesting juice without marking the monsters. Shoot the bug out without marking and it will travel in a straight line from your chest. It's much quicker and makes it easier to get the triple boost.
Always recall the insect immediately after it harvests an essence; it's much faster. You can tell when the wings are colored in the UI. It also helps you aim, though when you have enough practice you can set your bug up to flank a monster by sending it to the side and then aiming at the monster. If you send the bug 3x quickly without recalling it, it will do a charged attack. Only play around with that after you've mastered harvesting all juices from monsters without marking, though... You gotta get the basics before getting fancy.
Watch gaijinhunter's IG tutorial video; it will blow your mind.
Also: use small monsters in the area to grab some essences. They can be key to getting a triple buff on some monsters with hard to reach parts.