Answer: You're right, it's a difficult question! Have you tried yellow sticky traps? I'm not sure that the butterflies would not be attracted as well, but you could try putting a small trap in one area to see how effective it is. Just make or find some bright yellow pieces of cardboard (index cards work well) and smear them with petroleum jelly or spray them with 'Tanglefoot'. Mount them at plant level, or suspend them where butterflies can't reach but whiteflies can. The yellow color will attract the whitefiles. When they land, they'll get hopelessly stuck. It's worth a try!
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