Bemisia tabaci species complex, B biotype.

Bemisia tabaci species complex, AN biotype, also known as cotton whitefly.

The AN and the B biotype whitefly adults are both 1.5 mm long and cannot be separated visually. Adults hold their white powdery wings more like the roof of a house that does not quite join at the apex, so when viewed from above the body can be seen between the wings.

Nymphs are pale yellow-green and flat scale-like insects that attach to the underside of the leaves of their host plant. Most nymph stages are immobile. Once silverleaf whitefly B biotype becomes established in a location it tends to displace the AN whitefly.

Greenhouse whitefly, Trialeurodes vaporariorum.

Other biotypes of the Bemisia tabaci species complex.

The silverleaf whitefly is a pest of crops in Australia, Europe, Asia, Africa and the United States. SLW has been recorded in cotton crops from all areas in eastern Australia and from Katherine in the Northern Territory.

Only in Central Queensland has it reached levels regularly requiring the use of insecticides and occasional insecticide control is required in the Darling Downs, Byee and St George areas.

Cotton, soybean, peanut and many broadleaf weeds.

SLW eggs are laid haphazardly on the underside of leaves. The eggs are yellow-green, changing to dark tan as they are about to hatch. Leaves with high populations of whitefly eggs often have a dark patch on the underside.

The life cycle from egg to adult can be as little as 18 days in the summer, but longer in cooler weather.

The SLW can cause damage in several ways. Having a high reproduction rate and a short generation time, the large numbers generated can retard plants simply through feeding.

The insect secretes large quantities of honeydew that not only interferes with photosynthesis but causes problems with cotton fibre processing.

SLW is a carrier of viruses such as cotton leaf curl in Pakistan and the United States. These viruses are not known in Australia but should they enter the country the SLW is now available to spread them.

Proper identification and regular estimates of the number of adults and nymphs are important. SLW are usually found on the lower leaf surface and they affect all crop stages.

Chemical control

By permit only. A significant problem in the management of SLW is its ability to develop resistance very quickly to many insecticides when used repeatedly. There is variation for resistance in cotton varieties and breeding for host-plant resistance is under way in other countries. For current chemical control options see Pest Genie or Australian Pesticides and Veterinary Medicines Authority (APVMA).

Cultural control

SLW management in Queensland cotton will be based on a number of integrated controls such as:

• breaks in the cropping cycle and elimination of alternative hosts
• use of economic thresholds to determine whether control action with an insecticide is necessary
• use of appropriate insecticides such as insect growth regulators (IGRs) as required
• conservation of natural enemies
• an insecticide management to conserve susceptibility.

Parasitic wasps (Encarsia spp. and Eretmocerus spp.) commonly provide some level of biological control.

Predators include bigeyed bugs, lacewing larvae and ladybirds.

A management strategy needs to preserve and promote the activity of predators and parasites. Avoid early-season use of broad spectrum insecticides, particularly pyrethroids and organophosphates.