Peter uses:
Lumix DMC-G10
I am not familiar with that particular Panasonic but it is bound to have an exposure bracketing function as do most Lumix cameras.
As others have said, for a white butterfly, as a starting point adjust the basic exposure by -1 stop
and additionally, set it to exposure bracket around that - 1 by say 2/3 stop. Thus you will have three exposures set at -1/3, -1.0 and -5/3. One of these is bound to be satisfactory.
Other Panasonic Lumix models I have owned are capable of (not always achieved of course!) excellent results. The reviews of G10 suggest it is an very good camera (with a large sensor) but I would expect that it takes a lot of trial and error to get the best out of it.
Jack