Fighting dragons, saving citrus

Maintaining safety in the application of crop protection products

Scientists are facing a real-life challenge: how do you stop a particularly aggressive pest from spreading and destroying citrus plantations around the world, on the one hand not harming honey bees which may be foraging in the citrus trees while on the other hand ensuring the necessary treatment? An innovative area of study may address the problem by keeping bees away from the crop, allowing application whenever needed.

Fighting dragons, saving citrus


“Citrus Greening Disease is estimated to have killed over 60 million trees worldwide (10 million in Brazil alone), causing crop losses of up to 100 percent in countries such as South Africa.”

Source: FAO

Netting citrus trees

Netting is traditionally used to keep bees away from citrus trees during the blooming period.

In the last decade, the Yellow Dragon Disease, also known as Huanglongbing (HLB) or Citrus Greening Disease, has severely damaged the world’s citrus production. This bacterial disease, spread by an insect called the Asian Citrus Psyllid (ACP), has migrated from China into major citrus-growing regions around the world such as Florida, California and parts of Brazil. Once a citrus tree, such as lemon, orange or grapefruit, is infected with HLB, it will die. Currently, there is no cure, and the only prevention is to control the psyllid. Bayer has developed crop protection products to directly manage this insect so as to minimize the spread of HLB. The great challenge: For effective disease control there must be complete psyllid vector control, so application is needed at times honey bees may be present in the crop.

Ordinarily, registered crop protection products can be used safely without harming bees. In cases such as with the management of ACP, there are extremely few products available and some of them are intrinsically toxic for bees. Normally, they cannot be applied during flowering. However, due to the long flowering period of many citrus crops, if an infestation of the psyllid occurs, there is no option to wait until flowering is over. As a result, what is needed is a solution which allows for the application of intrinsically toxic products during flowering – without harming bees.

Feeder Station

At the feeder station, a research team member takes photographs as part of the monitoring process during the study.

Bayer’s North America Bee Care Center, the Chemistry Department in Research Triangle Park, North Carolina, and the Bayer Pest Control Department in Monheim have teamed up to lead a pioneering study on how to keep honey bees away from the plantation, when ACP must be managed in order to combat the spread of Yellow Dragon Disease. Dick Rogers and Tai-Teh Wu are the lead scientists behind this study alongside a dedicated research team who prepare and conduct many repetitions of exploratory and proof-of-concept experiments. Since late 2012, the testing has consisted of feeder station trials, microplot and semi-field trials and laboratory trials, to test numerous substances that might emit scent that keeps bees away – so-called repellents.

They also analyze methods of repellent delivery and measure potential effects on bees, both from a health and behavioral perspective.

The study theorizes that by ‘herding’ bees – guiding them away from specific locations using repellent substances – crop protection products can be applied while giving the greatest protection to local honey bee populations.

Feeder Station 2

Researchers observe bee reactions when drops of potential repellent substances are applied to feeder stations.

As citrus crops are usually not dependent on insect pollination, repelling bees does not influence fruit set. The first tests have already proved successful: “In one semi-field trial, 100 percent of honey bees were safely repelled for several hours, and there was reduced repellency for up to 24 hours,” says Wu.

Safety, efficiency, and practicality of any solution have been priorities from the study’s start. The research team began with a number of specific qualities they wanted for a bee repellent. According to Rogers: “The repellent needed to be safe for humans, animals and plants; easy to apply; provide a high level of short-term efficacy; be cost-effective; and it should be something that could be used in small quantities.” The study has already yielded valuable information. Rogers and Wu can state that the goal in agricultural systems should be using a targeted application of repellents. Field testing has shown that honey bees are more safely and effectively kept away from areas of potential exposure when repellents are targeted to more defined areas rather than widely sprayed over a field, for example.

Rogers and Wu have successfully identified a specific compound that might be used to repel honey bees. Therefore, it may play a significant role in deterring bees from visiting citrus during ACP crop protection treatment. The research team is convinced that repellents are an innovation that warrants further investigation and experimentation. Continuing this valuable research could lead to even greater precision in pest management and offer new possibilities to protect citrus and other crops.


Team leaders from Bayer Bee Health & Integrative Apiculture Research: Dick Rogers (left) and Tai-Teh Wu (right).



Rogers and Wu hope to expand the current bee repellent study to full project status. In addition to its application in citrus production, this process-product repellent method may be useful in other large-scaled field crops such as cotton, making application of crop protection products even safer for bees. With this study’s promising leads, there may be a meaningful way to combat the rise of Yellow Dragon Disease – while minimizing potential risks for honey bees.

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