The D-Limonene in many citrus products is a potent degreaser, and it melts the waxes insects use to waterproof their chitin shells. With out it, they lose osmotic pressure to almost all their major organ systems and die quickly.
I have some citrus bug killer, but it must be low on the limonene because it takes forever to work. Sometimes, I think the bugs just lick it off and run away.
If you want to use a biodegradable de-greaser, go with Simple Green. It's much cheaper, and fully-concentrated will kill very quickly. I discovered it's power one morning when a red wasp was flying around in the bathroom and landed just out of safe smacking range. I squirted the wasp to get it to move and it just dropped on the countertop, wiggled around a bit and checked out. I've utilized SG with great success against ants and roaches, as well. Killin' and cleanin' at the same time, what more could you want? A better smell, perhaps.
Disclaimer: I have not tried spraying Simple Green on a whole nest of angry wasps. If you do so, you are aware that the results are unknown and may include a silly, fear-driven dance viewed curiously by your neighbors, painful stinging, anaphylaxis, followed possibly by coma and/or death, most likely in that order. I would advise using the buddy system. If you are stung and find yourself having difficulty breathing and/or unusual swelling, your buddy can be standing by with epinephrine, antihistamines, grandma's secret poultice, and a phone to call 911. Better yet, have your buddy spray the wasps, while you observe from a safe distance.
