Wild bees play an important role in ecosystems and their protection is therefore crucial. While research shows that the sensitivity of wild bees to crop protection products is comparable to that of honey bees in many cases, wild bees exhibit great diversity of behavioral and ecological features. Scientists are currently developing new bee safety test procedures to safeguard these important pollinators.
With more than 20,000 species, wild bees make up a huge group of insects that, in contrast to their domesticated cousin the honey bee, have been very little studied to date. It is therefore important to study the safety of crop protection products in wild bees as well as honey bees.
Several research teams are working on adapting existing test methods for honey bees and making their findings applicable for other bee species as well.
New and adapted test procedures make possible more precise risk evaluation. Wild bee populations can then be better protected and will continue to make their contribution to a healthy ecosystem.
Take a walk in nature and you’ll encounter all different kinds of wild bees. On their way to forage nectar and pollen, they fly by us, each with their characteristic buzzing. Every wild bee species has its own special traits and different ecological features.
Currently, the honey bee is the best-researched bee species. For more than 30 years, required safety testing of crop protection products has included numerous studies with honey bees, including extensive and intricate trials in the laboratory, semi-field tests and field trials. Scientists are now striving to take a similar approach to assess the potential risk posed by crop protection products to wild bees. It stands to reason that tests cannot be developed for each individual bee species, and applying the same battery of tests to all bees is likewise not an option. It is a complex undertaking, as the group of wild bees includes over 20,000 species globally. As a consequence, researchers are evaluating the extent to which the test results from honey bees can serve as input parameters in the risk assessment for wild bees.
However, the features of a testing system to determine the potential effects of a crop protection product also depend on the tested bee’s biology, including factors such as specific behavioral features, feeding habits, life cycle and physiology. Scientists are therefore working on designing tests for various bee species, some of which are derived from the respective honey bee tests. This takes a lot of time and also makes the process very challenging. Progress therefore requires collaboration and knowledge from international experts.
Studies on wild bees currently focus on bumble bees, mason bees, leafcutter bees and stingless bees. Dr. Ivo Roessink, for example, an ecotoxicologist and scientist at Wageningen Environmental Research in the Netherlands, works as the chair of the Bee Protection Group of the International Commission for Plant-Pollinator Relationships (ICPPR), developing tests for solitary bee species. “We started off with very little knowledge about these bees. With every iteration, we raise questions that require empirically determined answers, improve the tests and examine their fit with regulatory requirements,” explains Roessink.
For the last three years, Roessink’s solitary bee team has been ring-testing study designs for two species of mason bee, Osmia bicornis and Osmia cornuta. In ring tests, researchers from various institutions and countries perform the same test in a series of iterative cycles. The results are examined and the test protocol and design are improved with each cycle, until everyone agrees that the test procedure is clear, doable and delivers consistent and reproducible data.
Wild bees comprise over 20,000 species globally.
Source: Bee Lab, University of Minnesota
“We observe these bees for four days – that’s enough time to find out what concentration of the crop protection product has no effect and therefore can be considered safe to use. Two test types are under development according to this procedure,” says Roessink. “We succeeded in finding a methodology for the acute contact test, which assesses the risk when wild bees come into direct contact with a crop protection product.” He and his team are also carrying out acute oral tests. “We also want to assess the risk of a bee eating contaminated nectar. In this type of test, we put the crop protection product in a cup of nectar for the bee to eat and then monitor it.”
To be able to carry out these investigations and observe the wild bees’ response, it is important to keep them comfortable in a lab setting. “For example, we provide these bees with bits of paper to climb on as they like to chew it. Apparently, this makes them feel comfortable, and they then display natural behavior. These are the crucial factors that make the study a success – we want to do the test with wild bees behaving naturally, not hiding in a corner.”
One challenge working with mason bees is the narrow testing window imposed by the natural life cycle of these animals, such as their hatching behavior. “Each spring you can get some tests done, but if hatching success is what you are measuring, you have to wait until the following year to collect data,” explains Roessink. The less that is known about the bees being tested, the longer the process takes to develop appropriate tests, simply because the information needed to make critical decisions must be collected first.
INTERVIEW: DR. IVO ROESSINK
Making wild bee testing possible
Meet Dr. Ivo Roessink, Senior Scientist at Wageningen Environmental Research in the Netherlands. He and his team work with the mason bees Osmia bicornis and Osmia cornuta to test the effects of crop protection products on wild bees.
Do crop protection products harm wild bees? If so, in what ways?
Crop protection products are designed to control certain insects. The key is: How are you using these products? So it’s important to look at the bigger picture. It’s not just the toxicity of crop protection products; it’s also about the landscape in which you perform your farming. Also, it’s crucial to use crop protection products at certain times to prevent wild bees from being exposed to them. For example, if we know that certain wild bee species only fly between 10 am and 3 pm, the farmer should apply the crop protection product later in the day to not conflict with the flight time of the bees. We are working on developing smart combinations like that to lower the exposure and to make the whole system safer for pollinators. That’s a promising way forward.
What are the main challenges that you face while
assessing crop protection product safety in wild bees?
From my experience, there are two distinct types of challenges. One practical problem is the issue of working with these wild bee species in a laboratory or semi-field setting. It is very hard to keep them alive in a laboratory setting. We had to start from scratch to learn how to work with the bees. That’s important before you can start testing them. The other challenge concerns the different behavior of wild bee species in the field. They don’t behave as predictably for us as honey bees. For example, some wild bees are only active early in the morning, some late in the afternoon and some only in spring. These factors make wild bee risk assessments very difficult for us. The ecology of wild bees will have an impact on exposure and therefore on the potential risk.
Could you give us an outlook on the future of crop
protection safety in wild bees?
Over the next few years, scientists will look at the molecular makeup of these bees. A honey bee has certain defense systems in its body, and wild bees may have such defense systems as well. So they may cope better or worse with toxicity. Maybe in the near future we will be able to assess sensitivity based on the defense systems of different bee species. That would be great because then we could only look at the defense system and wouldn’t have to do all of these tests with a lot of animals. That’s the future!
Bayer is working on the ring tests described above in collaboration with various international scientists. “We started trying out testing systems with leafcutter bees, allowing them to hatch in paper cups in the laboratory,” recalls Dr. Nina Exeler, who leads the Experimental Unit Bees at the Ecotoxicology Department of Bayer’s Crop Science Division in Monheim, Germany. “We promptly learned that if the bees emerge and find nothing of interest around them, like food, they will crawl back into their cocoons. Pulling them out of their cocoons is time-consuming and could harm them.” Exeler and her team found a cunning solution to this obstacle. “We designed a two-chambered hatching container. The cocoons are held in the dark in one chamber. The second chamber receives light and is connected to the first via a tunnel. This tunnel is wide, starting at the dark chamber, but narrows as you go to the light chamber, where the opening is set high off the chamber floor. Emerging bees are attracted to the light and wander into the second chamber, but they cannot find their way back to their cocoons because of the narrow, raised tunnel opening.”
As testing with wild bees progresses, it will be necessary to extrapolate knowledge gained from one tested species to make inferences about others and to devise protection strategies to safeguard them while keeping overall testing requirements manageable and meaningful.
Ultimately, this data can be used to uncover interspecies patterns that help define toxicity threshold values and support cross-species protection strategies. By creating methodologies, scientists have already laid the groundwork to obtain this knowledge.