Silverleaf whitefly – a devastating pest of fruit and vegetable crops
In Australia, and particularly in Queensland, silverleaf whitefly (Bemisia tabaci biotype B), is a pest in vegetable, cotton and grain legume production areas. Globally, it is also a severe pest of these crops and is considered one of the world's top ten invasive arthropods.
Silverleaf whitefly (SLW) damages crops by feeding, and through the effects of the honeydew it produces which causes sooty mould to grow on leaves and contaminates fruit produce and cotton lint.
It is also a vector of geminiviruses, but these have yet to become a major problem in Australia.
This whitefly is resistant to a wide range of insecticides and therefore management approaches that reduce reliance on insecticides are desirable for long term sustainability.
CSIRO undertook the challenge of identifying a possible biological control agent and after conducting all the necessary tests and receiving the release approval, first released the tiny wasp, Eretmocerus hayati, in Queensland in late 2004.
The wasp became established and in many areas growers modified their insecticide management practices to encourage the biological control insect.
Maximising the effectiveness of biological control
Given the dynamic nature of the silverleaf whitefly pest species and its rapid ability to become resistant to pesticides, it was important to develop the knowledge required to implement an integrated pest management plan which would maximise the effectiveness of the biological control agent.
The research team, funded by Horticulture Australia Limited, using the National Vegetable Levy, voluntary contributions from industry and matched funds from the Australian Government, focussed on finding out information about E. hayati and how it behaved in the environment.
This information was used in computer models to help with developing a set of management recommendations which combine the use of insecticides, natural control via biocontrol (E. hayati) and uptake of on-farm management practices which benefit the persistence of the control agent across the seasons and across the entire region.
Recommendations for getting the best out of hayati
Based on the results, the team have developed a list of ways that growers can get the most out of hayati:
- Determine if hayati is present on your farm. If not, conduct an inundative release prior to the peak SLW season.
- Plant a crop that is slightly-to-moderately susceptible to SLW prior to the peak SLW season.
- Avoid planting crops that are highly susceptible to SLW or control weeds in cane.
- Plant crops that are highly susceptible to SLW near a refuge such as a small patch of unsprayed crop. Consider releasing hayati into the unsprayed patch.
- Keep broad leaf weeds to a minimum.
- Monitor SLW numbers and spray only when necessary.
- Avoid insecticides that harm hayati.
Following these recommended actions will mean that SLW populations stay lower for longer and have the additional advantage of supporting other beneficial insects, which can help to keep a variety of pest insect numbers down.