The silverleaf whitefly, B-biotype Bemisia tabaci, first detected in Australia in 1999, has

become a major pest on cotton in central Queensland. The silverleaf whitefly is also found,

albeit in low numbers, in most other cotton districts in Australia. The silverleaf whitefly

represents a considerable threat to cotton production in Australia.

The objectives of this project were:

• To monitor whitefly species distribution on cotton.

• To use toxicological, biochemical molecular and genetic techniques to continue

investigate insecticide resistance mechanisms in B-biotype B. tabaci.

• To continue a resistance monitoring programme for B- biotype, B. tabaci.

• To devise and test resistance insecticide management strategies for management of

Bemisia tabaci in Australia.

The project has tracked the expansion of silverleaf whitefly into most cotton areas of New

South Wales and Queensland. Resistance monitoring has exposed serious insecticide

resistance problems in the silverleaf whitefly, including resistance the insect growth

regulators. Studies have demonstrated cross-resistance between the two insect growth

regulators that have been used on cotton in Australia. Resistance mechanism and synergism

studies, however, have provided the means to overcome most resistances in the silverleaf

whitefly. The research project has been an instrumental part of the central Queensland,

silverleaf whitefly, resistance management strategy, which, so far, has prevented “sticky

cotton” problems.

Major Outputs of this project have been:

• Results of this project have given a knowledge of the distribution and abundance of

whitefly species on cotton in Queensland and New South Wales. While the silverleaf

whitefly has expanded into most cotton areas, data show that Greenhouse whitefly,

silverleaf whitefly and native B. tabaci can co-exist on cotton.

• Insecticide resistance levels in the silverleaf whitefly can be very high and resistance is

easily selected for, thus emphasising the need to rotate chemistry. Resistance to the

insect growth regulator pyriproxyfen is of particular concern, because of the industry’s

dependence on use early season, to prevent silverleaf whitefly population build-ups Post

insect growth regulator use, pyriproxyfen resistance levels are so high, as to suggest that

consecutive generations of silverleaf whitefly are receiving pyriproxyfen. It is therefore

likely that the threshold based initiation of pyriproxyfen use, is giving a longer use period

in the area than is desirable. In 2004, post insect growth regulator use, pyriproxyfen

resistance was extreme and coincided with reports of poor control at Emerald.. Piperonyl

butoxide synergism studies with pyriproxyfen, however, showed complete suppression of

resistance and piperonyl butoxide synergism may become a very valuable tool in

prolonging the life of pyriproxyfen on cotton.

24

• This project has also developed technology for more effective insecticide synergism in

the field, for the control of resistant silverleaf whitefly. Using our patented concept

(Gunning, R. V and Moores, G. D. Method and Composition for Combating Pesticide Resistance

UK Patent no. 0309773.0, PCT/GB2003/001861),of microencapsulation of insecticides to

delay insecticide release until piperonyl butoxide has effectively inhibited the esterase

enzymes causing resistance, we have been able to overcome resistance. Field trials

demonstrated outstanding control with pyrethroids, against highly resistant silverleaf

whitefly. This resistance control technology can be applied to a number of esterase

mediated resistances in the silverleaf whitefly, such as insect growth regulators,

imidacloprid, the pyrethroids will lead to greatly improved control options for the

silverleaf whitefly.