Yeast can be transformed into a next generation pesticide and combined with sugary lure to kill spotted wing drosophila (Drosophila suzukii or SWD), an invasive fruit fly posing a major threat to soft fruit farming.
Invaded regions such as Europe have seen significant damage from SWD, which are native to Asia and difficult to control using current pest control methods. This has prompted considerable research exploring more potent alternatives.
Scientists from the Eck Institute for Global Health in Indiana have found that using RNA interference (RNAi), a process which introduces tiny RNA molecules into a cell, can silence what is known as the Shaker gene in the flies, causing neurological damage and death.
Turning baker’s yeast into a RNAi biopesticide
The researchers used a genetic engineering approach to make baker’s yeast (Saccharomyces cerevisiae) express a heat-inactivated biological pesticide which delivers the RNAi. In their latest research, they saw that making a paste using the yeast and a sugar bait, in this case flat Coca-Cola, can attract the pest flies, successfully controlling their populations under semi-field conditions.
They modified a soda bottle to continuously deliver Coke throughout the study. After initially feeding SWD in cages with their yeast-soda mix, they went on to release 50 flies in a free-standing mosquito net to test the approach over a six-day study. They also fed three species of mosquito and the related fruit fly Drosophila melanogaster the novel pesticide to test how specific it was to SWD.
Specificity and safety
The technique killed 96% of the SWD in the study, and critically, in their tests on the non-target insects, all of them survived. The researchers suggested that this because the target site of the RNAi is not present in the mosquitoes, and while even though it is present in D. melanogaster, the gene-silencing effects of RNAi don’t spread system-wide in the species.
Additional work will test the effectiveness of their pop-based lure in the field, while also assessing the ideal locations for bait stations.
“Although further evaluation of the RNAi yeast attractive targeted sugar bait feeders in the field is needed, RNAi yeasts targeting SWD may represent a new class of effective, yet biorational insecticides that can be used in integrated pest management programs for control of this destructive insect pest,” the researchers wrote in Pest Management Science.
From proof-of-concept to practice
Such pest management regimes may involve combining the sugar baits with pheromones, using them alongside SWD repellents as part of a push-pull control strategy or even developing a sprayable formulation of the novel pesticide.
Despite the promise, to employ such a technology commercially, there would be regulatory hurdles to overcome, the scientists conceded. This is because the DNA molecules used in the work have an antibiotic resistance marker, making it likely to fall foul of regulatory bodies. A move to a different yeast strain may be necessary, which has components necessary for RNAi success integrated into its genome. Such a yeast strain should also be more suitable for large-scale fermentation, they suggested.
Key takeaways
- RNAi yeast killed 96% of spotted wing drosophila in semi-field trials.
- The biopesticide targets a neurological gene essential to the pest’s survival.
- Sugar bait significantly improved attraction and control effectiveness.
- Non-target insects were unaffected in laboratory tests.
- Regulatory and scale-up challenges remain before field deployment.
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