Thryvon trait to manage thrips
How does double fruit retention and less insecticide applied sound? Pretty good!
Dr Kristen Knight is the technical development lead – insect traits at Bayer Crop Science’s Cotton Insect Resistance Management Centre in Toowoomba. She was delighted to see such positive results from their 2024 field trials of Australian cotton germplasm encoded with ThryvOn. ThryvOn is a genetically modified trait incorporating a Bt protein that provides season-long protection from thrips.
“This new Bt trait innovation is supporting sustainable Australian cotton by adding a mode of action to manage thrips to the existing control of lepidopteran pests,” says Kristen. “Australian field trials started 2017, and Bayer is planning a commercial release in 2028 of Bollgard 3 ThryvOn Cotton with XtendFlex Technology, providing growers with a cutting-edge insect and weed management package, pending all required regulatory approvals being in place.”
The ThryvOn trait is built on the integration of Cry51Aa2.834_16, a single pore-forming insecticidal protein produced by the bacterium Bacillus thuringiensis (Bt), into the cotton genome. Like the Bollgard trait proteins, ThryvOn protects the crop from the target pests throughout the season.
Although there are similarities to the proteins used in the Bollgard trait, the ThryvOn trait has no activity on Lepidoptera species (Bachman et al, 2017).
“Managing Bollgard 3 ThryvOn cotton will require growers to adopt a new paradigm compared to the Bollgard-alone trait,” she says. “Growers can expect to see a reduction in insecticide usage, however, monitoring for thrips must continue and the ThryvOn trait will be used in combination with insecticides as needed.”
Kristen says ThryvOn’s level of activity on thrips is comparable to that of insecticides. With fewer insecticide applications per season, there are benefits for beneficial insect populations, including predators of thrips, within ThryvOn cotton crops.
ThryvOn was commercialised in the USA a few years ago with activity against tobacco thrips and tarnished plant bug, two of the most important pests in mid-south USA
cotton production.
ThryvOn v thrips
Rather than ingesting a toxin when feeding, adult thrips actively avoid laying eggs on ThryvOn cotton plants. This is the major mechanism of plant protection from thrips damage, but it is not known how the thrips detect ThryvOn cotton.
Huseth et al. (2020) reported on trials in the USA that demonstrated adult female thrips laid 85 per cent fewer eggs in ThryvOn cotton compared to non-ThryvOn cotton, and only seven per cent of those survived to adulthood. The survivors were 20 per cent smaller and lived only half as long as thrips that developed on non-ThryvOn cotton.
If thrips eggs are laid and the nymphs cannot avoid the ThryvOn plants, they begin to feed, then stop feeding and die of starvation.
“ThryvOn cotton experiences less thrips damage due to a combination of reduced oviposition, reduced egg lay and less feeding by immatures, not direct mortality of the pest,” says Kristen. “The same avoidance effect is observed for both tobacco thrips at establishment and flower thrips later in the season.”
The evaluation trial at Griffith in 2023-4, measured the impact of thrips at establishment and at boll formation on ThryvOn cotton and non-ThryvOn cotton.
In this trial, all experimental treatments had the standard seed insecticide applied at planting, and no insecticide sprays were applied to the crops.
“By the 4-6 true leaves stage, the control treatment had sustained significant thrips damage,” says Kristen. “In contrast, the ThryvOn treatment established well and was growing vigorously.”
The differences observed between the ThryvOn and control treatments at flowering and fruit set are due to thrips suppression at establishment.
“Because the ThryvOn plants had little to no setback due to sucking pests at establishment, the plants set fruit at the fourth and fifth nodes,” says Kristen. “This is particularly important in cooler regions where slower establishment is the norm. As the trial progressed, we also measured higher fruit retention in the ThryvOn treatment.”
At this stage, only thrips data have been submitted for registration, but Kristen and the Bayer CropScience team continue to evaluate ThryvOn’s activity on other sucking pests across the Australian cotton industry.
In an evaluation trial at Narrabri in 2023-4, the team measured the impact to pests prior to flowering.
The site experienced some thrips pressure, with minimal loss of the top five fruit observed from the ThryvOn plots.
In late January 2024, Kristen visited the Narrabri trial and observed the agronomic benefit to the crop from the new trait under field conditions.
“The ThryvOn plants flowered 3 days earlier than the control and had retained fruit on the fourth or fifth nodes,” she says. “At this stage, no insecticide had been applied to the trial, so the differences we observed were all down to the interaction of the trait with sucking pests that were present in the trial plots.”
Preserving Bollgard 3 efficacy is essential for the delivery of ThryvOn in a few years time. Kristen says that growers and the industry need to maintain their efforts to preserve the technology for at least another eight to 10 years while Bollgard 4 moves toward commercial release.
“Continued excellence in stewardship will ensure the shift to Bollgard 4 with ThryvOn occurs with no field resistance in the Lepidoptera pests,” she says.
Left: Bollgard 3 cotton with XtendFlex technology control, right: Bollgard 3 ThryvOn cotton with XtendFlex technology. No foliar insecticide was applied to these evaluation trials.
Boll retention on Bollgard 3 ThryvOn cotton with XtendFlex technology was 50 per cent higher than on the Bollgard 3 cotton with XtendFlex technology control at the Narrabri evaluation trial.
Left Column: Bollgard 3 cotton with XtendFlex technology control (1-2 true leaves, 3-4 true leaves and 4-6 true leaves).
Right Column: Bollgard 3 ThryvOn cotton with XtendFlex technology (1-2 true leaves, 3-4 true leaves and 4-6 true leaves). No foliar insecticide was applied to the Griffith evaluation trials.
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