Eradication of the devastating silverleaf whitefly (SLW) from Australian vegetable and cotton crops is a step closer with CSIRO being granted permission to release a wasp as a biological control agent.

After extensive testing, CSIRO Entomology has been given approval from the Australian Government Department of Environment and Heritage and the Department of Agriculture, Fisheries and Forestry to release a tiny parasitic wasp Eretmocerus hayati which feeds on silverleaf whitefly (Bemisia tabaci Biotype B).

Silverleaf whitefly is only 1mm long but it is wreaking havoc on Australia's vegetable, cotton and ornamental plant industries. After hitching a ride to Australia from the USA in 1994, it has now spread to most mainland states. A crop under attack can host billions of whitefly, with every female being able to lay up to 250 eggs.

Silverleaf whitefly is known to attack more than 600 plant species but is particularly fond of broccoli, cabbage, cauliflower, cotton, cucumber, eggplant, soybeans, marrows, melons, squash, tomatoes and zucchini. In Queensland (Lockyer Valley, Central Highlands and intensive coastal horticultural areas) and the northern coastal areas of New South Wales, it is a major headache for producers.

Dr Paul De Barro from CSIRO Entomology says, "We have finished the evaluation of the tiny parasitic wasp which is even smaller than the whitefly. Eretmocerus hayati parasitises juvenile whitefly and has been successfully used in the Lower Rio Grande region of southern Texas which has a climate similar to the areas under attack in Queensland."

The first releases of the wasp will be made at Gatton in the Lockyer Valley and Bundaberg with subsequent releases at Bowen, the Burdekin and Emerald.

In 2000, outbreaks of this pest on vegetables in the coastal strip from northern NSW to the Burdekin in Queensland led to more than $6 million extra being spent on pest control. In 2001/02, it caused an extra $3 million to be spent on control on cotton in Queensland's Central Highlands. It comes with the added problem of resistance to many insecticides.

Dr De Barro says that whitefly is a problem for two reasons. It can cause direct damage and loss in yield through its feeding and the copious quantities of sticky honeydew which it produces lead to contamination with sooty mould. The latter is a particular problem for the cotton industry as the resultant 'sticky cotton' could threaten the quality of Australian cotton and so reduce its price.

The research on SLW was supported by Queensland Fruit and Vegetable Growers, Horticulture Australia Ltd, the Grains Research and Development Corporation and the Cotton Research and Development Corporation.