Bug killers can be bought in shop. Either a fly swatter or just those spray things, the plant(s) could, from time to time, have insects invading and we can just buy and kill it by /extermitebugs (or something). And every time we kill those pest, we can get some small points?
Bugs I'm more into, as long as it's not a definite detriment to the plant's growth - maybe a minor annoyance, ie the plant refuses to be watered until it has its bugs swatted or it slows the growth if they're present etc.