Emerging Plant Pests - silverleaf whitefly

Silver leaf whitefly (SLW) (Bemisia tabaci biotype B), is a small sap-sucking insect which occurs worldwide and was first detected in Australia in 1994. SLW is now found throughout Queensland, NSW, northern WA and the NT. It has also been recorded from glasshouses in cooler regions such as SA, VIC and Perth.

SLW is a pest of over 500 species of plants, feeding on many important crops and ornamentals. SLW is considered a pest as populations can reach high numbers very quickly, has a ravenous appetite and can transmit diseases, including diseases of tomatoes such as yellow leaf curl virus (TYLCV).

Life cycle

SLW can take between 18-28 days to develop from egg to adult in warmer weather and 30-48 days in winter. Its life cycle has the following stages:

1. Egg (hatch in about 7-10 days)                         
2. Crawler (lasts about 3-4 days)
3. Nymph (three moults - lasts about 6-12 days)
4. Pupa (doesn't feed - lasts about 4-6 days)
5. Adult (commonly lives for 9-16 days, can live up to 50 days)

Adults

SLW adults are small (1mm), white and their wings are held tent-like over their bodies. They are usually found feeding on the underside of leaves which is also where they lay their eggs. They will disperse in clouds when disturbed.

Adult Silverleaf whitefly (1mm)

Eggs and Nymphs

Eggs are laid on the underside of young leaves. "Crawlers" hatch from the eggs and are the only mobile stage of the juvenile SLW. They crawl a short distance and settle in one spot where they stay until they develop into adult SLW.   Below are images of  (L) Silverleaf whitefly eggs (C)  Silverleaf whitefly nymphs 2nd & 3rd instar (R)  Silverleaf whitefly pupae.  The (C) and (R) images are courtesy of G Webb.

(0.2mm)                                   (0.4 - 0.6mm)                          (0.6 - 0.8mm)

Damage and disease transmission

SLW feed on plant juices using piercing-sucking mouthparts causing stunted growth, leaf yellowing and uneven ripening of fruit. SLW excrete honeydew during feeding, on which sooty mould readily grows, causing blackening of leaf and fruit surfaces.

SLW thrives on hundreds of ornamental and crop plants such as alfalfa, broccoli, cabbage, cantaloupe, cauliflower, cotton, cucumber, tomato, squash, peanut, capsicums, beans, and watermelon. Ornamental hosts include poinsettia, hibiscus, lantana, verbena, canna lilies, crepe myrtle, petunia, rose, and bottle brush.

SLW transmits many plant diseases including yellow leaf curl, caused by TYLCV, which causes severe losses in tomatoes. This virus has been recently detected in tomato crops in south east QLD. For more information see DPI&F note on yellow leaf curl viruses. SLW also transmits Tomato Australian leaf curl virus (ToLCV-Au), which is present in the Northern Territory and in far north Queensland, but not in any Queensland tomato production areas to date.

Movement and dispersal

Adult SLW are weak fliers but once airborne they can travel long distances by the wind (commonly 2km, but up to 7km). All stages of the life cycle are likely to be carried on plant material and cut flowers of host species.

Control

Monitoring

Inspect plants by checking for adults, pupae, nymphs and eggs on undersides of leaves. Use of yellow sticky traps can detect SLW infestations in their early stages.

Physical

Keep unused growing areas empty when possible (and remove plants around the perimeter of the screenhouse which may harbour SLW). Dispose of infested plants and plant debris in sealed plastic bags to prevent reinfestation. Also inspect other host plants for yellow leaf curl and remove any that are diseased.

Chemical controls

A few things to consider when applying chemical control include:

• Foliar pesticides are effective when there are mostly crawlers, nymphs or adults
• Soil systemic pesticides may provide a better overall control
• Plant surfaces including the undersides of leaves need to be covered for foliar pesticides to be effective
• Avoid consecutive treatments with the same chemical as SLW has a good ability to develop resistance to insecticides.

Consult a pesticide dealer for more information about which pesticide works best for your situation. Always read and follow pesticide label instructions and/ or permit conditions before use.

Biological control
The use of natural enemies is considered one of the main ways to manage SLW in the long term and the introduction of exotic parasitic wasps as part of biological programs has proved successful in many parts of the world (including Australia). In these places the agents have considerably reduced the impact of SLW.

Further information

• If you require any further information please contact the DPI&F Business Information Centre on 13 25 23 (free call in Queensland) for advice on what to do next.  Alternatively contact your nearest DPI&F office or email the DPI&F Business Information Centre: callweb@dpi.qld.gov.au.

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last reviewed 29 March 2006