Well my beetles don't discriminate - they love them all - lol. Maybe they aren't attracted to Julia because she doesn't stay a good yellow color for long.
For the roses = 1 cup of DE to 1/2 gal of water into a spray bottle. Keep agitating the bottle. If it rains you have to repeat. It does leave a residue = green leaves with white polka dots. Actually it looked kinda cool. For the slugs, sprinkle directly on the ground ( dark damp places). I read DE does not harm earthworms. If you want to really get rid them = Sevin. Spray, wait 2-3 days and repeat. I'll give you the directions if you want. Ya the Milky spores works but it is my understanding you have to do it once each year for 2 - 3 consecutive years.