Integrated pest management of citrus gall wasp and Fuller’s rose weevil (CT19009)

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.