Adults of many whitefly species are white, but the nymphs can be different colors, such as black.
However, if the flies have both black and white markings, could these be fungus gnats? These grayish black gnats feed on organic matter and are a common pest of houseplants (including plumerias). They are especially troublesome if the soil does not dry out between waterings (dry to a depth of about 1 to 2 inches deep), or if water remains in a saucer underneath the pot. The flies will lay eggs in the soil, and the larvae will feed on organic matter, algae, and fungus, and will also nibble on roots; they’ll mainly inhabit the top 2 or 3 inches of soil. Fungus gnat larvae are of special concern for young plants but can sometimes be a nuisance for established ones. The adults do not feed on plants (or bite humans), but the numbers of flies flitting around the plant can be irritating. For more about this pest and its control, see: https://www.almanac.com/pest/fungus-gnats
Some controls/preventions include: Place yellow sticky traps around the plant to catch adults so that they can’t lay eggs. Repotting with new soil, cleaning the pots, isolation, etc., are all good things to try to control these pests. (Plants outside, however, can pick up more fungus gnats and other pests, so be sure to inspect them and their soil before bringing them indoors.) Be sure that pots have drainage holes and a well-draining potting mix. You might also try adding about a 3/4- to 1-inch-deep layer of horticultural sand on top of the potting soil to deter adult flies from laying eggs in the soil. Keep the soil free of debris, such as fallen leaves.
Hi, Jo An,
For best control, try to identify what species these black and white tiny flies are; your county’s Cooperative Extension might be able to help you.
https://www.almanac.com/cooperative-extension-services
Adults of many whitefly species are white, but the nymphs can be different colors, such as black.
However, if the flies have both black and white markings, could these be fungus gnats? These grayish black gnats feed on organic matter and are a common pest of houseplants (including plumerias). They are especially troublesome if the soil does not dry out between waterings (dry to a depth of about 1 to 2 inches deep), or if water remains in a saucer underneath the pot. The flies will lay eggs in the soil, and the larvae will feed on organic matter, algae, and fungus, and will also nibble on roots; they’ll mainly inhabit the top 2 or 3 inches of soil. Fungus gnat larvae are of special concern for young plants but can sometimes be a nuisance for established ones. The adults do not feed on plants (or bite humans), but the numbers of flies flitting around the plant can be irritating. For more about this pest and its control, see:
https://www.almanac.com/pest/fungus-gnats
Some controls/preventions include: Place yellow sticky traps around the plant to catch adults so that they can’t lay eggs. Repotting with new soil, cleaning the pots, isolation, etc., are all good things to try to control these pests. (Plants outside, however, can pick up more fungus gnats and other pests, so be sure to inspect them and their soil before bringing them indoors.) Be sure that pots have drainage holes and a well-draining potting mix. You might also try adding about a 3/4- to 1-inch-deep layer of horticultural sand on top of the potting soil to deter adult flies from laying eggs in the soil. Keep the soil free of debris, such as fallen leaves.
Hope this helps!