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A combination of agrochemicals shortens the life of bees, as a study shows

Publicado em 31 maio 2019

A recent study by Brazilian biologists suggests that the effect of pesticides on bees may be worse than previously thought. Even if an insecticide is considered non-fatal, it shortens the life of the bees by up to 50 percent. The researchers also found that a fungicide that is safe for bees alters workers' behavior and makes them sluggish, potentially jeopardizing the survival of the entire colony.

The results of the study are published in Scientific Reports . The lead investigator was Elaine Cristina Mathias da Silva Zacarin, a professor at the Federal University of São Carlos (UFSCar) in Sorocaba, São Paulo State, Brazil. Researchers from the São Paulo State University (UNESP) and the Luiz de Queiroz College of Agriculture (ESALQ-USP) from the University of São Paulo also participated in the study. The main researcher of the project is Osmar Malaspina, professor at the UNESP in Rio Claro.

Several bee species are endangered worldwide. The phenomenon has been observed in Europe and the United States since 2000 and since at least 2005 in Brazil. In Rio Grande do Sul, the southernmost state of Brazil, the loss of approximately 5,000 colonies was reported between December 201

One of the most commonly affected species is Apis mellifera ] the western honeybee, which is of European origin and the source of most commercially available honey. Hundreds of indigenous native Brazilian species can also be affected in the natural environment. The economic impact is considered immense, as most agricultural crops depend on pollination by bees.

The reason for this sudden mass disappearance is also well known – it is the indiscriminate and improper use of agrochemicals, including insecticides, fungicides and herbicides, and acaricides (pesticide pesticides). Bees are contaminated when searching for food and bring the toxic chemicals with them when they return. Within the nest, the chemicals are taken up by larvae, which shortens their lives and affects the functioning of the entire colony.

"Soya, corn and sugarcane monocultures in Brazil rely on intensive use of insecticides, for example bee colonies are contaminated when farmers spray their fields at the recommended safety distance of at least 250 meters between a crop and the surrounding forest There are people who spray to the edge of the forest, "said Malaspina In Europe and the US, bee colonies are gradually dying out. One to five months may pass between the first report on bee mortality and the destruction of the colony. It's different in Brazil. Here the colonies disappear in just 24 or 48 hours. No illness can kill a whole colony in 24 hours. That can only be an insecticide. "

Malaspina recalled that the insecticides, fungicides, herbicides and acaricides used in Brazil contain hundreds of active ingredients." It is impossible to test each person's effect in the laboratory. The money is not available, "he said.

A study was conducted between 2014 and 2017 by Colmeia Viva, an initiative of the Agrochemical Industry Association (SINDIVEG).

The researchers collected material in 40 communities across the state To identify agents that could be linked to bee mortality from the 44 most sprayed plants in the state of São Paulo, in collaboration with beekeepers, farmers and agrochemicals, they developed a set of recommended measures for the protection of apiaries and the Implementation of best practices in agriculture and the minimum margin of safety for the use of the agrochemicals already mentioned.

Risks of combined exposure

The scientists believe that the positive effects of the Colmeia Viva counseling program could now be evident. While in Rio Grande do Su 5,000 colonies disappeared, losses were lower in Santa Catarina and Paraná, the other two states in the south, and in the state of São Paulo.

"However, that does not mean that São Paulo bees are no longer threatened by agrochemicals," said Zacarin. "We are beginning to conduct tests to measure the effects of combined exposure to insecticides and fungicides on honey bees, and we have already discovered that a particular fungicide does not harm bee colonies when sprayed alone, but becomes toxic to bees when associated It does not kill them like insecticide, but it does change their behavior and endanger colonies. "

The drugs tested were clothianidin, an insecticide used to control pests that infest cotton and dry beans, corn and soybeans, and pyraclostrobin , a fungicide that is applied to the leaves of most cereal and fruit crops, legumes and vegetables.

We looked for realistic values, such as those found in flower pollen, "Zacarin said.

This is an important point: any highly sprayed agrochemical almost instantaneously decimates bee colonies, and investigates the subtle effects of the medium to long term "We want to find out how the residual effect of agrochemicals affects even very small amounts on bees," explained Zacarin.

Behavior change

The experiments were carried out in a laboratory to prevent environmental pollution. A. mellifera larvae were harvested from healthy colonies, divided into groups, placed in graft cells, and fed on a diet of royal jelly and sugar mixed with a minute dose of one or another of the agrochemicals between the third and sixth day after transmission. The dose was a few nanograms (billionths of a gram).

The diet of the control group pe contained no agrochemicals. Diets of the second and third groups were contaminated with either the insecticide clothianidin or the fungicide pyraclostrobin. Both the insecticide and the fungicide were added to the diet of the fourth group of larvae.

"When larvae are six days old, they become puppets and begin the metamorphosis that develops as adult workers," Zacarin said. "In the wild the life of a worker bee lasts on average 45 days." "When these bees are confined to the lab, the lives of these bees are shorter, but the lives of the specimens we fed with a diet that was very small The insecticide clothianidin has been drastically cut by up to 50 percent. "

No effect on the lifespan of workers was observed from larvae fed with food contaminated solely by the fungicide pyraclostrobin. "Based solely on this finding, we can assume that a very small dose of the fungicide is safe, but unfortunately this is not the case," Zacarin said.

At the larval or pupal stage no bees died, but the behavior of the fungicide adult workers have changed. They were sluggish compared to the control group.

"Young workers do daily inspections of the hive and therefore have to travel some distance and move a lot in the colony.We have discovered that bees alone are contaminated with the fungicide, or when both the fungicide and the insecticide taken together travel much shorter distances and move much slower, "said Zacarin.

If a significant proportion of worker bees were equally affected in an actual hive, this change in behavior would affect the functioning of the entire colony and could be one of the reasons for the observed mass extinction.
The diet of the control group pe contained no agrochemicals. Diets of the second and third groups were contaminated with either the insecticide clothianidin or the fungicide pyraclostrobin. Both the insecticide and the fungicide were added to the diet of the fourth group of larvae.

"When larvae are six days old, they become puppets and begin the metamorphosis that develops as adult workers," Zacarin said. "In the wild the life of a worker bee lasts on average 45 days." "When these bees are confined to the lab, the lives of these bees are shorter, but the lives of the specimens we fed with a diet that was very small The insecticide clothianidin has been drastically cut by up to 50 percent. "

No effect on the lifespan of workers was observed from larvae fed with food contaminated solely by the fungicide pyraclostrobin. "Based solely on this finding, we can assume that a very small dose of the fungicide is safe, but unfortunately this is not the case," Zacarin said.

At the larval or pupal stage no bees died, but the behavior of the fungicide adult workers have changed. They were sluggish compared to the control group.

"Young workers do daily inspections of the hive and therefore have to travel some distance and move a lot in the colony.We have discovered that bees alone are contaminated with the fungicide, or when both the fungicide and the insecticide taken together travel much shorter distances and move much slower, "said Zacarin.

If a significant proportion of worker bees were equally affected in an actual hive, this change in behavior would affect the functioning of the entire colony and could be one of the reasons for the observed mass extinction.

Researchers still do not know exactly how the fungicide affects the behavior of bees. "Our hypothesis is that when it is combined with an insecticide, pyraclostrobin reduces the energy metabolism of the bee, and further studies are underway to elucidate this mechanism," Zacarin said.

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Further information: 
Rafaela Tadei et al., Late Effect of Concurrent Exposure of Larvae to the Insecticide Clothianidin and the Fungicide Pyraclostrobin in Africanized Apis Mellifera, Scientific Reports (2019). DOI: 10.1038 / s41598-019-39383-z

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A combination of agrochemicals shortens the lives of bees, study shows (2019, May 31)
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