Well, usually if it's a bug with great attack or special attack (like genesect) I like to go with a huge special set. That's why many people use the bolt,beam,thrower combo. They're all special and there all good type coverage. Personally on Genesect I like to go with t-bolt, ice beam, flamethrower, and bug buzz. On a defensive bug (Like Shucke) you may want to keep it defensive, expecially because it has 5 speed, 10 Attack and special attack. Personally, I go with a set like this: Toxic, Substitute, Stealth Rock and Rest, while it's holding a lum berry, of course. Usually I use the steel bugs because, they're good defensive Pokemon that can phaze(foretress) and fight(Heracross,Genesect,Scizor, and Escavalier). But, others in there can fight too. Like Scizor, it's known for being a BAWS. Scizors can crush your opponent with attack while still holding up their great defense. in my opinion, this is the best set: Iron Head, X-Scissor, Iron Defense, and Swords Dance. In a mono bug, I wouldn't put all bug steels. I'd go with Genesect, Shuckle, Leavanney, Scizor, Forretress, and Volcarona. Genesect is BAWS, Shuckle is VERY defensive, Leavanney is for those litle situations, I don't have to explain Scizor, Foretress is a big fat Phazer, and throws out hazards, and Volcarona is for type coverage. Nuff said here. Because I'm not gonig to get into serious detail (unless I get bored) I'll post the moveset for each, but not the ability, item(Exept for Shuckle), evs or nature. Sadly, unlike usual, also no IVs :)
Rest(with Lum berry)
And, because BB wanted it, I'm giving a set for Beautifly, too.