Whiteflies

Classification and Description:  Whiteflies (Homoptera: Aleyrodidae) are small insects that feed as nymphs and adults on plant sap with piercing-sucking mouthparts.  With rare exceptions, the bandedwinged whitefly (Trialeurodes abutilonea) is the only species that infests cotton in Tennessee.  Adult bandedwinged whiteflies are only about 1/16^th inch in length, and as the name implies, have gray bands across white-colored front wings.  Eggs are yellowish and very small (0.1 mm).  Nymphs and pupae reach a maximum size of about 1 mm in length and ½ mm in width.  They can occur at very high numbers.

Hosts and Distribution:  Bandedwinged whiteflies have a very wide host range that includes weedy and cultivated plants.  Besides cotton, they are pests of many ornamental, greenhouse and vegetable plants.  This species is native and widely distributed throughout the United States, especially the South.

Life History:  Whiteflies are not flies but actually much more closely related to aphids.  They have a unique biology.  Tiny yellowish eggs are generally laid on the bottoms of leaves, and all life stages are typically found in the same place.  Hatching eggs produce “crawlers,” which over a period of 2-3 days move only a few inches before settling into an immobile nymph stage.  The immobile nymphs feed on phloem (sap) until they molt into pupae.  Whiteflies develop rapidly from the egg to the adult stage (12-14 days at summertime temperatures), and they have many overlapping generations per year. 

Pest Status and Injury:  Whiteflies are usually not a serious threat to cotton grown in Tennessee.  Heavy infestations generally weaken plants and cause leaves to wilt and yellow.  Honeydew excretions from feeding nymphs will accumulate on plants, giving them a sticky but shiny appearance much like aphid infestations.  Sooty mold growing on honeydew can cover leaves and stain the lint.  This is generally not a serious problem in the Mid-South because rain will often “wash” the lint.  However, the accumulation of honeydew and sooty mold is an indication of heavy infestations that may need to be treated with insecticides. 

Management Considerations:  Whiteflies are found on the underside of leaves, so insecticide coverage is a potential problem.  Systemic insecticides generally provide the best control.  Because they do not feed, eggs and pupae are relatively difficult to kill with insecticides, and two applications at about a five day interval may be necessary.  Insecticides recommended for control of bandedwinged whiteflies are listed in the Insect Control Recommendations for Field Crops (PB1768).  The current treatment threshold is when 50 percent of plant terminals are infested with adults, particularly when honeydew in accumulating.

Print-Ready PDF Publication (Whiteflies W023)