- Q biotype Bemisia tabaci adult. Photo: Z. Ludgate
- Pale yellow-green nymphs. Photo: S. Subramaniam
Q biotype of the Bemisia tabaci species complex was identified in Australia in late 2008 and early 2009 from collections from vegetable crops in the Bowen/Burdekin region and cotton at Wee Waa, New South Wales, and Goondiwindi, in Queensland.
The Bemisia tabaci species complex is represented in Australia by three distinct biotypes: Australian Native (AN), silverleaf whitefly (SLW) or B biotype, and Q biotype. These morphologically identical and can only be separated using chemical (enzyme) or molecular (DNA) techniques.
Q biotype behaves in a similar manner to B biotype. In large numbers it causes feeding damage to horticultural crops, is a vector of significant whitefly transmitted diseases and may cause honeydew contamination in cotton. It can be very difficult to manage as it has the ability to rapidly develop resistance to some insecticide groups, particularly if they are used repeatedly.
Ongoing monitoring by DEEDI staff since early 2009 has not detected any Q biotype from either cotton or horticultural production areas in QLD and NSW. While Q biotype may be present in Australia, it does not pose a management risk at this stage.
Bemisia tabaci species complex Q biotype
Bemisia tabaci whitefly adults are 1.5 mm long and 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 established in a location it is expected to displace the Australian native whitefly.
Greenhouse whitefly, Trialeurodes vaporariorum
Other biotypes of the Bemisia tabaci species complex
The home range of Q biotype extends from Spain across North Africa into Egypt and the Middle East including Israel and Jordan. It has since spread via the ornamental nursery trade to China, France, Italy, Japan, the Netherlands and the United States.
A wide host range (more than 500 species), similar to that of B biotype
The life cycle of Q biotype is the same as that for all B. tabaci. 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.
Q biotype 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. Q biotype 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 Q biotype, like B biotype, is available to spread them. The concern is that any new incursions, whether Q or B, could bring with them viruses that are not present in Australia.
|Monitoring and action level|
Proper identification and regular estimates of the number of adults and nymphs are important. Whiteflies are usually found on the lower leaf surface and they affect all crop stages.
Chemical control: A significant problem in the management of Q biotype is its ability to develop resistance quickly to some insecticide groups, particularly if used repeatedly. For current chemical control options see APVMA.
Cultural control: Management of whitefly in Queensland cotton will be based on a number of integrated controls such as:
|Conservation of natural enemies|
Parasitic wasps (Encarsia spp. and Eretmocerus spp.) commonly provide some level of biological control. Predators include big-eyed 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.