The insects that leave white powder are Mealybugs and Whiteflies.
Mealybugs are the most common bug or insect that leaves white powder.
A Mealybug is a tiny and white soft bodied insect that produces a white colored, powdery wax which looks similar to cotton.
Mealybugs will often nest in areas of a plant that are protected such as the undersides of a leaf or where branches meet.
Mealybugs are not harmful although they can be fatal to plants as the mealybugs drain the plants of water and nutrients.
Whiteflies are tiny winged insects which also leave behind a white colored, waxy powder on the underside of plant leaves.
Whiteflies also produce a sticky honeydew and when disturbed the whiteflies will take flight and make them easy to spot.
Mealybugs are most commonly found outdoors, where they often infest perennial plants like fuchsia, gardenia and hibiscus, as well as citrus trees and grapes.
Mealybug insects are very small, oval shaped and white in color.
Whiteflies are Hemipterans that typically feed on the undersides of plant leaves.
The whiteflies comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea.
More than 1550 species of whiteflies have been described.
Whiteflies are not harmful to humans and do not bite humans or animals in the same manner as mosquitoes or fleas.
Instead, whiteflies feed exclusively on plant sap and are not known to cause direct harm to humans or animals through biting or feeding.