Researchers have found that even at doses too low to kill, agricultural chemicals impact the color preference, respiration and locomotion of native stingless bees in South and Central America.
Their study, published March 17 in Science of the Total Environment, points to the importance of extending ecological studies of pollinators to include bees other than the honeybee, which are the focus of most current pollinator research.
"I think we have an intimate relationship with honeybees because we know that honeybees are useful for making honey and providing services in agro-ecosystems like pollination," said study author Khalid Haddi, an entomology professor at Universidade Federal de Lavras in Brazil. "We asked ourselves if honeybee was the best model under all conditions, knowing we have a lot of native pollinators and other insect species. Could we, in our context, use other insects?"
The trend of using honeybees as a model organism for pollinators has emerged from their perception as the world's most frequent pollinator. But they hardly have a monopoly on pollination.
A 2018 study from Proceedings of the Royal Society found that honeybees account for 13% of all flower visits by pollinators worldwide. While this is massive for a single species, it is far from the majority of all pollination. The same study indicated that 49% of plant species are not visited by honeybees at all.
Many of the rest rely on other pollinators, including native bees. While honeybees are only a single species of bee that originated in Southeast Asia, there are over 20,000 species of bee native to all parts of the world that play a role in pollination.
Haddi and his colleagues focused their study on the stingless Partamona helleri of South and Central America. They sought to use it as a non-honeybee model organism to learn more about the impacts on native bees of agricultural chemicals, including chemicals that do not target insects at all.
"A lot of studies have been focusing on insecticides that we use to target insects, but many other products that are used are being forgotten, like fungicides," Haddi said.
The researchers tested both honeybees and Partamona by allowing them to feed for five hours on minute doses of the insecticides and fungicides dissolved in a honey solution. Twenty-four hours after exposure, they performed bioassays monitoring the bees' locomotion, respiratory rates and color preference.
Bees perceive color differently than humans. They are unable to see the color red because its wavelengths are too short, but they can see ultraviolet patterns on flowers that help them home in on them. So color preference in bees is a critical factor in their feeding and pollination.
The team found that both insecticides and fungicides altered the color preferences of stingless bees, causing them to prefer blue more and yellow less. Meanwhile, only fungicides altered respiration or locomotion.
Even extremely low, sublethal doses of fungicides — what Haddi described as "what you might encounter two or three days after spraying" — impacted more aspects of the native bees' behavior than insecticides. This is a grim finding when considering that fungicides do not even target insects.
These effects were different than those observed when honeybees were subjected to the same experiments. While both species experienced similar changes in color preferences, they experienced different changes in locomotion and respiration.
For example, worker bees of the native species increased their locomotion when exposed to fungicides, and honeybees did not.
The findings demonstrate that while honeybees remain a critically important natural resource, it is important to expand the scope of ecological research and conservation efforts to include native bees.
"We have an interest in understanding human impacts on insects," Haddi said. "And when we think about insects, we think not only pest insects, but also other insects that provide ecological services, including some biocontrol agents, and of course pollinators, which are very important."
The findings also shows that the native Partamona helleri bee is an important model organism for studies on native bees in the neotropical region, and more broadly speak to the need to expand scientists' toolbox of model organisms in pollinator studies.
"We need to adapt our testing methods for the overall risk assessment of agrochemicals to the local, regional and national contexts," Haddi said. "We have seen that these stingless bees, which are very widely encountered, are very sensitive and susceptible to these chemicals compared to honeybees. So honeybees are not the best model to use."
The study, "Sublethal agrochemical exposures can alter honey bees' and Neotropical stingless bees' color preferences, respiration rates, and locomotory responses," published March 17 in Science of the Total Environment, was authored by Carlos H.S. Almeida, Pedro F.S. Toledo, Sarah M. Rezende, Weyder C. Santana, Raul Narciso C. Guedes, and Eugenio E. Oliveira, Universidade Federal de Viçosa; Khalid Haddi, Universidade Federal de Viçosa and Universidade Federal de Lavras; and Philip L. Newland, University of Southampton.