Answer: Orchids are very sensitive plants so your best course of action is to wash the aphids off, then place yellow sticky traps near the plants to attract any remaining aphids.
You can make your own traps by smearing bright yellow squares of paper with petroleum jelly or 'Tanglefoot' (available at garden stores). The aphids will be attracted by the yellow color and when they land, they'll be hopelessly stuck.
Good luck with your orchids!
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