This might be a silly question but have you tried soapy water? Regular Dawn dish soap works well. Pure castile soap seems to work better. 1tbsp per gallon of water. Drench the whole plant. That will start to knock them back. Repeated application should help but wont eliminate the problem.
I alternate spraying weekly with bacillus thurigenis and lacto bacillus with a little whey protein powder mixed in after the first true leaves form and continue spraying all season. This keeps pretty much everything at bay here in East Tennessee. But it only works if I start at the beginning of season and carry through all summer.