The native northeastern uruçu bees (Melipona scutellaris), jataí (Tetragonisca angustula) and mandaguari (Scaptotrigona postica) are more sensitive to the pesticide thiamethoxam (TMX) than Apis mellifera – a stinging species introduced in the country and adopted as a model for toxicological tests for the approval of agricultural pesticides.
This is what a study carried out by researchers from the Federal University of São Carlos (UFSCar) in partnership with the State University of Campinas (Unicamp) and the State University of São Paulo (Unesp) showed. By evaluating, for the first time, the impact of TMX on three native and stingless species, the study offers support for the development of public policies aimed at protecting pollinating insects in Brazil. The reduction in bee populations, in addition to being a serious environmental problem, has negative repercussions on agricultural productivity.
“Brazil has more than 2 thousand species of bees. Among the stingless ones there are almost 500 species. It's a huge diversity. Of course, it is not possible to carry out toxicological tests on all of them and with all pesticides, but it is necessary to select some species, in addition to Apis mellifera, to understand how it is possible to create a better configuration to protect these insects in the country”, says Osmar Malaspina, professor at the Unesp Biosciences Institute in Rio Claro and coordinator of the Research Group on Ecotoxicology and Bee Conservation (Leca) and the Working Group for the Development of Methods for Toxicity Tests on Native Brazilian Bees with the International Commission for Plant-Pollinator Relations (ICPPR).
The study, supported by Fapesp and published in the journal Environmental Pollution, is part of a larger project, whose objective is to expand understanding of the impact of pesticide use on the population of native stingless bees (also called indigenous bees) and support the creation of new protocols and laws related to the use of agricultural pesticides in the country.
This is because, currently, the toxicological tests that integrate the risk assessment of pesticides follow the guidelines established by the Organization for Economic Cooperation and Development (OECD) and are practically restricted to the species A. mellifera as a biological model. However, the debate about the need to reassess the environmental risk of pesticides has grown in recent decades, especially in tropical and subtropical regions, where there is greater diversity of bee species.
“Stingless bees are highly affected by pesticides, but tests are usually carried out only with A. mellifera, which is a stinging species that was introduced in Brazil. It is a species of European origin”, explains Roberta Cornélio Ferreira Nocelli, professor at the Center for Agricultural Sciences at UFSCar in Araras, coordinator of the Working Group for the Development of Methods for Toxicity Tests on Native Brazilian Bees at ICPPR.
In the recently published study, researchers performed a sensitivity curve to compare the impact of the pesticide in different scenarios, in addition to evaluating sensitivity to TMX per gram of bee, as size varies between species.
“The results showed that A. mellifera is more tolerant to TMX than the three species of stingless bees in all scenarios we evaluated. As we created a sensitivity curve, it is possible to analyze different scenarios as well, as we take into account the weight of the bee and other parameters related to pesticide consumption. This is because there are some differences in toxicity when only consumption or consumption and weight are taken into account”, explains Ana Paula Salomé Lourencetti, first author of the article.
Therefore, in relation to the average lethal concentration determined for the three species of stingless bees, TMX proved to be most harmful to uruçu, followed by jataí, mandaguari and finally A. mellifera. As for the analysis of the average lethal dose and taking into account the weight of the bees (dose per microgram), M. scutellaris was the most sensitive, followed by S. postica, T. angustula and A. mellifera. In mean lethal dose analyzes without taking into account the weight of the bees, T. angustula was the most sensitive, followed by M. scutellaris, S. postica and A. mellifera.
“The results of the work show that, for some species, A. mellifera can be considered a good parameter, but for others, it is not. Therefore, it is an indication that we need to more carefully evaluate toxicity tests aimed at releasing pesticides, as they are not being 100% efficient in protecting native Brazilian bees”, says Nocelli.
Public policies
Previous studies have already shown that bees' sensitivity to pesticides varies according to size, life cycles, metabolism, behaviors, biology and exposure routes. Therefore, the researchers emphasize, the extrapolation of toxicity data regarding A. mellifera to other species of bees with social and solitary behavior has been questioned for years.
In relation to stingless bees, in addition to these issues that confer greater sensitivity, the risk occurs because they are species abundant in crops and extremely exposed to pesticides.
For these reasons, the group of researchers is developing a new protocol (in the process of standardization) for stingless bees, which includes possible biological models for the environmental risk assessment process. The work, coordinated by the researchers and financed by the National Council for Scientific and Technological Development (CNPq), aims to expand toxicological tests on a greater number of bee species to support the approval and renewal of registration of agricultural pesticides.
“Ibama [Brazilian Institute of the Environment and Renewable Natural Resources] has a risk assessment system that is unique for bees in Latin America. However, it is very similar to that adopted in Europe and the United States for registering pesticides. Therefore, we are working together with environmental agencies to create a protocol that covers toxicity tests on native stingless bees. Public policy must be based on a standardized protocol and we did not yet have this for native species”, says Nocelli.
The researcher explains that, currently, in addition to A. mellifera, there is a protocol for three other species (Bombus terrestrial, Osmia cornuta and Osmia lignaria). “However, these are also from the Northern Hemisphere. Of the three species covered in the protocols, none are native to Brazil. And one of our biggest questions is whether these tests carried out with A. mellifera guarantee safety for our bees”, she says.
The initiative to develop new protocols that consider native species is a pioneer in Latin America. “This is a complex problem that needs to be resolved. In this case, Brazil is at the forefront. Even the legislation that requires testing with A. mellifera is the only one in South America. This only exists in the United States and Europe. Now we need to move forward on this issue of native stingless bees, especially because most of these species are native and do not exist in the Northern Hemisphere. It is of interest to us, as they are extremely important in terms of pollination. We need legislation that protects them", highlights Malaspina.
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