Integrated pest management of citrus gall wasp and Fuller’s rose weevil (CT19009)
What’s it all about?
This investment is improving the management of citrus gall wasp and Fuller’s rose weevil, two of the most significant insect pests of citrus in Australia. Through establishing a better understanding of the biology and ecology of the pests and providing more effective monitoring and management tools for growers, this project will contribute towards improving the productivity and quality of citrus grown in Australia.
For citrus gall wasp, an updated online management guide will be produced, with new information obtained from this project as well as an updated online timing tool for nationwide prediction of citrus gall wasp emergence. For Fuller’s rose weevil, options will be presented to industry for new monitoring approaches and alternative chemical options.
Specifically, the project is addressing the following areas…
Understanding the spread of citrus gall wasp in Southern Australia
Through a PhD study, the factors responsible for the increase in citrus gall wasp populations in southern Australia will be examined, allowing the industry to develop more robust and sustainable management strategies. Suspected reasons for the recent distribution expansion include changes in climates, movement of citrus seedlings and agronomic practices.
Updating the timing guide for citrus gall wasp emergence
An online timing guide was developed in project Development of national strategies to manage citrus gall wasp (CT15006) and is currently available for the prediction of the emergency of adult citrus gall wasps and eggs hatching in the Riverina, Sunraysia and Riverland. This project will expand the application range to Perth in Western Australia and Mundubbera in Queensland.
Developing novel monitoring tools to guide the timing of Fuller’s rose weevil control
Improved monitoring techniques are needed to time Fuller’s rose weevil control methods, as branch shaking is a labour intensive method and is difficult to standardise. This project will explore whether machine vision is a viable alternative monitoring method for integrated pest management with reduced maintenance compared to traps.
Exploring cultural control of citrus gall wasp with lucerne borders and/or inter-rows
Anecdotal evidence suggests that the presence of lucerne will attract lucerne seed wasp which has several parasitoids that may attack citrus gall wasp. Conversely, citrus gall wasp parasitoids may attack lucerne seed wasp, which could prove useful in future rearing for biological control of citrus gall wasp. This project will explore this further.
Investigating commercially available entomopathogens for Fuller’s rose weevil control
Entomopathogenic nematodes and fungi are organisms that can infect and kill insects in the soil and can potentially be used as biological control agents for many insect pests. Some have demonstrated potential for Fuller’s rose weevil control – but this concept needs to be investigated further.
Screening soft chemical options for citrus gall wasp and Fuller’s rose weevil control
For sustainable management of these pets, alternative chemical options, preferably those that are relatively ‘soft’ on beneficials are urgently needed. There is a risk of potential loss of the chemicals that are currently registered for pest control. Alternative options need to be reviewed on their efficacy and impact on beneficials.
Over the past six months, the project team has (1) completed a field trial investigating the impacts of three new chemicals on citrus beneficials, (2) set up a demonstration trial for controlling the citrus gall wasp (CGW), and (3) commenced a field trial of a new chemical for controlling the Fuller's rose weevil (FRW).
Spinosad and spinetoram demonstrated high efficacy in controlling CGW adults and EXP-A in controlling FRW adults in previous laboratory screenings. A field trial was conducted in the Riverina to investigate the impacts of the three new products on citrus beneficials. Applied at their label/recommended rates, spinosad was found to be toxic to a common generalist predator of citrus pests, the green lacewing, and Exp-A to the mealybug destroyer, Cryptolaemus ladybird. Spinetoram and Exp-A did not cause significant mortality to the lacewing. Similarly, neither spinosad nor spinetoram caused significant mortality to the ladybird. In a separate laboratory experiment, spinosad was found to be highly toxic to the red scale parasitoid, Aphytis spp. Spinetoram is likely similarly toxic to Aphytis spp as it is a related product to spinosad. All three chemicals reduced the total abundance of lacewings in the field.
A demonstration trial was set up in October 2022 in three blocks of citrus heavily infested by CGW in the Riverina to investigate the yield impacts of CGW. Preliminary results showed that both Surround® and Samurai® reduced new-season galls by over 90 per cent. Yield impact data will be collected next season.
A field trial of Exp-A has been set up in the Riverina to estimate its field efficacy in controlling FRW adults relative to a registered product. Results from this trial will be included in the next reporting period.
Entomopathogenic nematodes (round worms that live parasitically inside insect host) and fungi have been used as biocontrol agents of agricultural insect pests.
To find non-chemical means to control Fuller’s rose weevil (FRW) and citrus gall wasp (CGW), the project team investigated:
- Two commercial entomopathogenic nematodes for controlling FRW larvae.
- Six experimental entomopathogenic fungal strains and a commercial fungal product for controlling FRW and CGW adults.
The nematode investigation was conducted as a field trial in a block of navel orange trees in Leeton, NSW, in 2021. Significant reductions in adult FRW activity were observed in nematode-treated plots relative to the control plots in the five weeks following nematode application.
However, the reduction was not accompanied by a corresponding reduction in proportions of FRW contaminated fruit. The project team also tested the nematodes on FRW adults in the laboratory and found both nematode species killed the adult weevils under special conditions.
Of the five experimental fungal strains tested, only one showed potential for FRW control, either inactivating or killing the adult weevils. The commercial fungal product showed no efficacy against the adult weevils. The same fungal strains and an additional fungal strain were investigated in the laboratory for controlling CGW adults and in potted trees for controlling CGW larvae. None of the six strains demonstrated any efficacy in reducing CGW oviposition or controlling CGW larvae. Two strains showed moderate efficacy against CGW adults.
Outcome of findings:
Entomopathogenic nematodes and fungi both need humidity to thrive. While they have shown some encouraging results, it is challenging to rely on them for controlling FRW and CGW in the semi-arid regions of the Australian orange production centres.
- Investigations in the PhD study showed variations in the sex ratio, survival, and parasitism among regional CGW populations. These findings contribute to our understanding of CGW population dynamics.
- New technologies were investigated to improve FRW monitoring. FRW damage and adults in beat sheets can be detected by imaging, demonstrating the feasibility of using smartphones to monitor FRW in the future. One-year's monitoring data showed that Tedder traps provided more accurate estimates of FRW abundance than the industry standard branch-beating.
- Finding new management options for CGW control has been identified as a priority by the Australian Citrus Industry. Laboratory screenings have identified three promising new chemical options for CGW control and one for FRW control and showed that these chemical options can be used at below label/recommended rates without compromising efficacy.
- Entomopathogenic fungi and nematodes have also been investigated as potential non-chemical options for CGW/FRW control. Promising strains/isolates of fungi and nematodes are yet to be found.
Since the last update, the project team has:
- Completed the one-year scoping study of Fuller’s rose weevil (FRW) and citrus gall wasp (CGW) monitoring with machine vision, which demonstrated monitoring potential, detecting FRW on beat sheets with 77.5% accuracy and CGW galls and age with 75% precision
- Collected four sets of dose-response data of CGW to spinosad and spinetoram and one set of dose-response data of FRW to EXP-A, with the data showing that label rates of the three insecticides can, at least, be halved without losing efficacy for CGW/FRW control
- Developed a preliminary CGW population model, with results suggesting that CGW population will eventually come down in places with established parasitoid populations
- Analysed FRW monitoring data collected by early October 2021, which showed that Tedder trap provided more accurate indications of local FRW abundance than the industry-standard monitoring method of branch shaking.
Since the last reporting period, the project team have completed two laboratory bioassays of new direct- and residual-contact chemicals for controlling CGW adults. The research identified four potential new chemicals, with two appearing to be particularly promising. Potted-tree bioassays on new systemic insecticides for controlling CGW larvae is underway for completion next spring.
Early stages of the machine vision investigation showed encouraging results for automated counting of FRW on beat sheets, along with the identification of specific light wavelengths to distinguish old and new CGW galls. Further imagery will be collected to refine the machine vision algorithms. CGW emergence data from WA and QLD and parasitism data from the lucerne interplanting site will be analysed in the coming months.
The project team are engaging with growers and industry to share results as research progresses.
This program is a strategic levy investment in the Hort Innovation Citrus Fund