Every time my sims go to collect bugs they get stung by bees, so I never really bothered with bug collecting at all. This means I never bothered with adding new bugs, either.

I don't know exactly what to do with the bug collections on the Free Time tab either, but if it's there it should be possible to edit it. BACK UP THE NEIGHBORHOOD FIRST! If you accidentally do something like turning your sim into an unreadable object, this will be the easiest way to fix it. And keep the backup for a while. Sometimes errors don't show up for a few weeks in real time, especially in the memory. 

The normal editing process would be to click the desired area. (And probably wait, since I'm fairly sure the bugs are going to be stored in the neighborhood memory. Grab a good book.)  Then manually enter the new value, Commit, and save. You might need to find a bug you want to add and right click on it. If you have a backup to restore, you are free to experiment. Just remember that SimPE is right-click happy, so if you can't figure out what to do when you have only left-clicked something, try right clicking it. Also remember that no matter what you did, even if you clicked "Save", you have usually made no changes unless you clicked "Commit" first. It is willing to save with uncommited changes, but you spend 5 minutes saving absolutely nothing new.

You can also ask at MTS to see if anyone there has some better help.