Bug guts left on your paint will start to etch into the clear coat. My guess is this bug splat has been left on your truck for a while and you are now trying to get it off. Well it has done damage to your clear coat and you will need to use some type of paint cleaner to get it out. I realize that link is for a bird dropping, but it's the same principle, the clear coat has been etched, and they used M105 to get it out. Search around Meguiars
online forum, they have some great information there! Good luck.