Whiteflies are not flies. They belong to the insect order Homoptera, which includes aphids and mealy bugs. Like aphids and mealy bugs, they are a nuisance, because they multiply rapidly and can destroy plants quickly if not controlled. Getting rid of the whiteflies may be a long process that can entail using pesticides. It is important to take preventive measures when gardening if you want to keep whiteflies under control.
Whiteflies are tiny insects that coat their bodies with a white substance; hence the name. They destroy plants in two ways. They take the juice from the plants, causing them to wilt or die; and they also secrete a sticky substance that attracts mold. These molds grow on the leaf surface, blocking the sunlight.
There are 10 fairly common varieties of whiteflies: Greenhouse, Silverleaf , Ash, Banded Winged, Iris, Woolly, Mulberry, Giant, Citrus, and Crown. Whiteflies multiply rapidly. In some areas, such as California, they breed all year by laying their eggs on the underside of the plant.
After the adults lay their eggs, the eggs hatch into small flies in 4 to 12 days. They then go through four stages, called instar nymph stages. The first stage is the crawler stage, and is hard to see with the human eye. The crawlers move around for a few hours and then become still. They continue to go through the second, third and fourth instar nymph stages until they become adult. In each stage, the fly continues to suck nutrients from the plant's leaves.
Whiteflies are difficult to get rid of, because they multiply so rapidly. Some natural prevention methods are effective. Plant marigolds, Calendula and nasturtiums around your susceptible plants. These are repellent plants. Use a seaweed spray and mist your plants in the spring or before you bring them into the house. To rid your plants of whiteflies, you can vacuum the flies, use insecticidal soap or (for extreme outbreaks) use Pyrethrum, which is a botanical poison.
Even if you treat the whiteflies, they will probably return. It's difficult to eliminate all the whiteflies, because they can crawl into many crevices and hiding spaces within the plant. You may want to consider Orthen Fogger or Bifen Fogger. The fogger will get into the areas that other remedies cannot.