Whiteflies

   The silverleaf or sweetpotato whitefly biotype B (Bemisia tabaci) and the greenhouse whitefly (Trialeurodes vaporariorum) can build up to high numbers in cucumber. A mixture of both whiteflies is frequently found on cucumber. An accurate identification of the whitefly species present is important in order to make correct crop management decisions. High densities of the silverleaf whitefly have caused various disorders in tomatoes, squash, and leafy vegetables while similar densities of the greenhouse whitefly have not. Growers should thus learn to distinguish between the two major whiteflies. With some practice, growers can distinguish the species by examining the pupal cases with a hand lens. Whiteflies feed on plant sap and can reduce plant vigor and yield when populations are very high. Both whitefly species infest a very wide range of host plants including vegetables, ornamentals, field crops, and weeds. Whiteflies, like aphids, secrete honeydew, which is a sticky liquid that is a substrate for sooty mold. Whiteflies have six life stages- the egg, four nymphal stages (the fourth nymphal stage is commonly referred to as the pupal stage), and the adult.

     The silverleaf whitefly was so named because of the disorder it can induce on certain cucurbits. On susceptible crops such as squash, the leaf surface becomes silvered. The silverleaf disorder, probably caused by a toxin injected by the whitefly, has not been observed on cucumber. The average life cycle is 39 days from egg to adult but this period will vary with temperature. The pupal case of the silverleaf whitefly is dome shaped and has few filaments along its outer edge. The sweetpotato whitefly transmitted gemini virus, which has resulted in stunting and reduced fruit size in Florida and California, has not yet been detected in Hawaii. These viral diseases remain a great threat to Hawaiian agriculture. The average life cycle of the greenhouse whitefly is 32 days from egg to adult but this period will vary with temperature. The pupal stage is caked shaped with many tiny filaments around the outer edge.

    Both whiteflies are resistant to many pesticides. Insecticidal soaps and oils are widely used for whitefly control. These materials require thorough coverage of the leaf underside for effective control. These insecticides are relatively mild on natural enemy populations. Area wide control strategies are necessary in areas where whitefly numbers are abnormally high. Natural enemies include parasitic wasps, ladybird beetles, and fungal diseases. Consult with your local county extension agent or Entomology Specialist for an update on recent developments for whitefly management and control.