This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Kelly’s citrus thrips (KCT) was the key pest of citrus in the Riverland-Sunraysia (R-S) region. The scurfing and rind bleaching that resulted from KCT feeding reduced fruit quality, thereby reducing the packout of export quality fruit and rendering some fruit unsaleable.

The management of KCT was restricted to the use of foliar insecticides at the time. Building on the foundations laid in project CT97007, this new project aimed to expand the insecticidal and biological control options available for KCT control, and to start to integrate and optimise these control options.

The key outcomes were:

• Substantial levels of organophosphate resistance were shown to occur in KCT populations in R-S citrus.
• Baseline susceptibility levels and ‘discriminating doses’, that allowed quick diagnosis of any shifts in resistance, were calculated for three existing and four new candidate insecticides for KCT control.
• Two new foliar sprays (Actara™ and Success™) were effective for KCT control, but each had ‘off-target’ impacts on a key beneficial insect of citrus.
• A complex of soil-dwelling mites was predacious on KCT in R-S orchards, and factors that appeared to influence the abundance of these predators were identified.
  • Together, these findings provided for the first time the basis for an effective biological alternative to the insecticidal control of KCT.
• The fungal insect pathogen, Metarhizium, was an ineffective tactic for KCT control.
• Ground application of the insecticide bifenthrin could reduce KCT emergence from treated soil. This may have been an effective alternative treatment if targeted at lemons (an important KCT breeding source).
• The phenomenon whereby exposure of an insect to sublethal pesticide doses increased its egg production was unlikely to have contributed to the 1990’s rise of KCT as a serious new pest.
• There was no large-scale regional movement of KCT in the R-S.
• KCT in this region was largely a ‘self-contained’ population cycling within citrus.
• Growers’ understanding and practice of correct thrips identification and effective monitoring and spray control, and their awareness of the resistance threat and the biocontrol research developments were all improved.

Future R&D was required to develop an effective insecticide resistance management (IRM) strategy, to field trial several new insecticidal controls, and to enhance KCT biocontrol in citrus orchards.

The researcher recommended that citrus growers should ensure correct thrips identification, frequent monitoring from petal fall to Christmas, accurate spray timing and good spray coverage to get good control of KCT. If poor spray efficacy occured, and coverage was deemed to have been good, a sample of KCT should be tested for insecticide resistance. They also recommended that the citrus industry should encourage Syngenta and Dow Agrosciences to swiftly advance the registration applications of new chemistry for KCT control, devise and implement an IRM ‘rotation’ strategy, and support endeavours to further enhance KCT biocontrol.