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Silverleaf whitefly, a pest of cotton

Adult silverleaf whitefly (2 mm long)

Importance

The silverleaf whitefly (SLW), Bemisia tabaci B Biotype was first discovered in Australia in 1994. There is a native B. tabaci in Australia that is morphologically indistinguishable from the SLW. The biotypes can only be distinguished using chemical (enzyme) or DNA techniques. The native biotype is quite common on cotton but causes no problems.

Hosts of the SLW include at least 500 crops and ornamental plants worldwide and it is a pest on many of them. Cotton growers in the United States are faced with losses of up to $500 million annually, directly and indirectly from the SLW.

Distribution

This insect now occurs in all cotton areas, where it is readily found on a range of ornamental plants (poinsettia, duranta, hibiscus and lantana) in nurseries, and on ornamental plants and weeds in the field. Many of the large quantities of cruciferous, solanaceous and cucurbitaceous crops grown in Queensland are hosts of the SLW. It is a major threat to the Australian cotton industry. The first large-scale outbreak of this pest in cotton in Australia occurred in the 2001-02 season in the Emerald irrigation area. Subsequent outbreaks have occurred in other cotton growing regions including the Darling Downs, St George and Byee regions. The SLW has developed as a significant problem for the horticulture industry, with outbreaks in the Bowen/Burdekin region of Queensland.

Damage caused to plants

The SLW can cause damage in several different 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 sticky honeydew that not only interferes with photosynthesis but causes problems with cotton fibre processing. This whitefly is a highly efficient carrier of viruses such as cotton leaf crumple virus and cotton leaf curl virus. None of these viruses are known to exist in Australia.

Resistance to insecticides

A significant problem in the management of this pest 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.

Pest management

A complex of predators and at least 12 species of parasitoids (sometimes giving high parasitism rates) have been found in Australia, so the prospects for biological control are promising.

Silverleaf whitefly management in Queensland cotton will be based on a suite 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 regulants (IGRs) as required; 
  • conservation of natural enemies; and
  • an insecticide management program to conserve susceptibility.

The DPI&F, funded in part by the Cotton Research and Development Corporation (CRDC) is intensively examining the cotton areas of Queensland for the seasonal phenology, hosts and natural enemies of the SLW. Such a study will provide basic information fundamental to the development of integrated pest management (IPM) strategies.

Further information

Last reviewed March 2006.