Most greenhouse whiteflies are very resistent to pesticides. It is also hard to kill the adults who just fly off.
Purple ladybugs are the best white fly predator. Unfortunately the reason for the cyclical nature of whiteflies has much to do with the predator/prey cycle. The ladybugs eat a lot of whiteflies and when they eat most of them, the predator numbers dwindle until the whitefly numbers rise again. It is a two year cycle. Two years of bad whiteflies followed by 2 years of relatively manageable infestations. BTW these ladybugs bite.
If you have this bug and the larvae in your area, 9 were released in Hawaii to control whiteflies initially and they thrived.
Plant corn, it attracts ladybugs. Actually the aphids do, but the ladybugs will eat the whiteflies too.
Ant control. Ants will farm the nymphs so ants bait needs to be used to control them.
White flies have their favorite plants and some weeds. You need to eliminate the weeds and keep an eye on their favorite plants. Early control is a must.
Like slugs and snails, it is impossible to get rid of them entirely. The adults fly away and fly in from the neighboring areas so you just have to do the best you can.
1. A blast of water from the hose under the leaves to knock off the eggs and nymphs. Favorite plants for them are tomatoes, beans, peas, hibiscus, eggplant, pepper, poinsettia, plumeria, and papaya. (pretty much any tasty plant with broad leaves). You have to do this daily to annoy them to death.
2. Alcohol, horticultural oil do work but you need to be careful not to spray on hot days or the plants can burn. If the plants are in pots, it is more effective to dunk them head first in a solution of insecticidal oil or soap (do not use soap on peppers), for a few minutes every three days to get thorough coverage.
3. For heavy infestations on their favorite plants. Cut back the plants that can take it and make sure you bag and seal the remains. The adults will fly off so you will have to keep checking the remaining plants and don't let them get established.
4. I plant corn to eat but it also attracts the purple ladybugs better than any other plant. The regular ladybugs do eat whiteflies but not as much as the ladybug predator.
5. It does not make sense to purchase predators because most of them will not stick around if you have not provided a habitat for them. They need to have water, shelter and host plants that will provide nectar for the adults. Once the food is gone, they will take off. You cannot use other insecticides if you go the beneficial route. You will kill off the predators faster than the pests.
Happy gardening in Hawaii. Gardens are where people grow.