What are the implications?
Overseas studies indicate Q biotype has the capacity to develop resistance to many insecticides including insect growth regulators (IGRs) such as Admiral® and neonicotinoids like Confidor®. High levels of resistance to Admiral® have been detected in horticultural crops in a few locations in north Queensland and some field control problems have been observed for Admiral®.

Resistance testing from cotton production areas for the 2008-09 season has not shown any alarming resistance levels to Admiral® to date.

Overseas where populations are predominately of Q biotype, moderate to high resistance has developed to Admiral®. Where populations were mostly B biotype, Admiral® has retained high efficacy. This has been the case in Queensland where, according to Dr Gunning, B biotype populations remain susceptible to Admiral® and have a higher susceptibility to neonicotinoid insecticides, compared to Q biotype populations. At this stage Q biotype is showing markedly less resistance to pyrethroids than the B biotype.

In Israel, Q biotype has not developed resistance to Pegasus® despite several years of reliance on this product. In horticultural areas, significant resistance to Pegasus® was not found in either biotype.

Integrated Pest Management
Practicing good IPM principles can discourage Q biotype numbers from building up. Under natural conditions, B biotype will out-compete Q biotype. However, in an environment of high insecticide use, the more insecticide resistant Q biotype tends to displace B biotype, and once this shift occurs B may not recover to its former levels. Limiting the amount of chemical used against insect pests may favour the dominance of B over Q.

Q biotype, like B, has the capacity to vector the virus that causes cotton leaf curl disease. This disease is not present in Australia. The main risk is that any new whitefly incursions, whether Q or B biotype, could carry viruses that are not present in Australia.

Identification
Q biotype and B biotype can not be distinguished visually. They can only be distinguished by looking at small differences in their DNA or biochemical make-up.

WE NEED YOUR HELP
In order to determine the distribution of Q biotype, we are asking growers and consultants to send in whitefly specimens to the Queensland Primary Industries and Fisheries, Toowoomba. Please refer to details at the bottom of this article.

FURTHER READING

Whiteflies http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_10277_ENA_HTML.htm

The Cotton Industry Biosecurity Plan Appendix 3 provides information on Q biotype (page 32) and Cotton Leaf Curl Virus (page 40).
http://www.planthealthaustralia.com.au/project_documents/uploads/Section%209%20Appendix%203%20Pest%20Risk%20Reviews.pdf

Follow this link to the Fact Sheet on Q biotype whitefly. http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_13554_ENA_HTML.htm

WHITEFLY SAMPLING
Adult whiteflies: In fields where whitefly are present, collect a minimum of 30 adults from random plants throughout the crop. Place these in 65% alcohol (watered down methylated spirits) in a leak proof vial or bottle. Note that >70% alcohol is classified as a dangerous liquid and should not be sent via post or courier.

Immatures: In fields where whitefly are present, collect a minimum of 30 leaves from random plants throughout the crop. Aim to collect leaves that have large immature scales (4th instar/red-eye nymphs) on their underside. Collect only 1 leaf/plant. Pack the leaves into a paper bag and then inside a plastic bag.

For live material, send by overnight courier to:
Richard Lloyd
DEEDI, Primary Industries and Fisheries
203 Tor St, Toowoomba Q 4350
Ph: (07) 4688 1315

Ensure samples are clearly labeled and include the following information:
Collectors Name, Phone No., Fax No., Email address
Farm Name, Field, Postcode, Region (e.g. Gwydir)
Date of Collection, Host Plant (Crop)
Comments

Article by Zara Ludgate and David Murray

Resistance testing for the 2007-08 season indicated no alarming results for Admiral® (pyriproxyfen) or Pegasus® (diafenthiuron) in cotton areas. The IRMS guidelines for Admiral® require that only 1 spray may be applied per season. Apart from the cost involved, more then one Admiral® spray has been shown to increase the development of resistance.

As part of the management strategy for whitefly it is important to know what species or biotypes are present as these will significantly impact on the management decision that is required. Refer to past beatsheet articles to read more on identifying the different species and biotypes of whitefly.

We are seeing mixed populations of whitefly across Queensland. On the Darling Downs, greenhouse whitefly (GHW) has made up >90% of the population in the Norwin area. A sample from Theodore showed the whitefly population was made up of 70% SLW and 30% GHW.

In Emerald, a limited number of Pegasus® sprays have been applied for SLW. Pegasus® is best used for early season suppression of SLW at low insect densities or as a late season knock down to prevent honey dew contamination of open bolls.

Very few (if any) Admiral® sprays have been applied so far this season. Admiral® may be applied after 1450 day degrees if SLW numbers reach high densities. Remember that only one Admiral® spray may be applied per season to limit the potential for resistance to develop.

An excellent publication has been produced through the Cotton CRC by Richard Sequeira and Tracey Farrell That outlines thresholds and sampling methods for SLW in cotton in more detail (www.cottoncrc.org.au/files/5743fee2-f978-4a79-a9d1-9b1800e899cf/Whitefly_Management.pdf). This should be referred to when making management decisions for this pest.

In Emerald, there were high levels of natural control of whitefly from the parasitic wasps, Eretmocerus hayati and Encarsia formosa. Parasitism levels of 40% and 75% were recorded in two fields in the Emerald Irrigation Area. In a field at Biloela, parasites were so abundant that the tiny wasps were clearly visible walking around on leaves.

It is likely that the high parasitism levels recorded in Emerald and Biloela are due, in part, to very limited mirid sprays earlier in the season. This has avoided flaring SLW and allowed beneficials to multiply and offer a free service to growers and consultants in controlling whitefly.

Whitefly numbers are reportedly building up at St George/Dirranbandi. DPI&F entomologists will be visiting the area next week to collect samples for resistance monitoring and check parasitism levels.

While whitefly are definitely starting to make their presence felt in cotton fields across Queensland, their presence does not necessarily warrant action. Monitor fields often as whitefly can build up exponentially, identify what species/biotypes are present, use the available thresholds and avoid flaring whitefly by minimising the use of disruptive insecticides and maintaining beneficials in the system.

Article by Zara Ludgate