Developed to kill insects that harm crops, insecticides naturally affect bees, invertebrate animals that are extremely important for pollinating agricultural crops and wild plant species.
The use of less toxic molecules that degrade quickly, allied to a management of the application of the products, however, can minimize the damages to the colonies of bees and, consequently, to the plantations and to the biodiversity.
This is what a study published in the journal Science of the Total Environment shows by researchers from Portugal and Brazil, the latter supported by Fapesp.
“The adverse effects of insecticides are well known on bees and there are several laboratory studies showing this. We wanted to understand how this action took place in more realistic field conditions, and we managed to manage it using different techniques, so that the application of the insecticide minimally affect these pollinators”, says Caio Domingues, who carried out the work as part of his doctorate at the Center for the Study of Social Insects at the São Paulo State University (CEIS-Unesp), in Rio Claro, with a grant from Fapesp.
According to Osmar Malaspina, a professor at CEIS-Unesp who participated in the study, bees play an essential role in pollination, including important agricultural crops in Brazil, such as soybeans, oranges and coffee.
“Our group's research over the last 20 years shows how insecticides can be harmful to bees, which has contributed to the manufacturers themselves, together with producers, starting to seek ways to reduce this impact”, explains the researcher, who coordinates the project “Bee-agriculture interactions: perspectives for sustainable use”, supported under the BIOTA-FAPESP Program.
The experiment described in the study was carried out in the district of Castelo Branco, in Portugal, during an internship carried out by Domingues at the University of Coimbra. The group analyzed hives of the species Apis mellifera iberiensis
Two similar areas of 25 square kilometers were selected, with a high density of eucalyptus plantations ( eucalyptus globulus ) and 15 kilometers apart. In the center of each one, an apiary with five colonies each was installed and, in addition, an observation colony, or “sentinel”.
Experiment
The insecticide application was carried out at the end of May, with high infestation of the main pest of the crop, the eucalyptus weevil ( gonipterus platensis ). The researchers also verified that in the period there was not a great availability of resources, such as pollen and nectar, in the entire landscape and especially in the place where the insecticide was sprayed. So it is known that the bees were not leaving the hives much to collect.
“In addition, recommendations for using the product and ideal environmental conditions were followed, such as adequate temperature and wind speed, in addition to the absence of rain for up to 24 hours after application”, says Domingues, who is currently a researcher at the University of Maribor , in Slovenia.
Analyzes for residues were performed on the first day after application of the pesticide and again 16 days later. The bees themselves, honey and bee bread, a product from the processing of pollen with honey and glandular secretions produced by insects, were analyzed.
In the area that did not receive insecticide, no residues of acetamiprid were detected in the colonies. And in the other, where the product was applied, most samples had no detectable amounts. The concentrations detected, in turn, were 52 times below the so-called sublethal levels, those that do not cause immediate mortality.
In addition to these measurements, the researchers weighed all the frames in the colonies to monitor the development of adults and offspring over the study period. Analyzing photos of the nests and resources of the colonies with the use of artificial intelligence, a software identified and classified the contents of the cells in the combs, such as larvae, eggs, pollen, nectar, honey and others.
Trays installed in front of each colony were used to calculate mortality during monitoring, as well as to observe possible unusual mortality events.
“There were no significant differences between the colonies in the two areas. This does not mean that the acetamiprid residues did not reach the bees, however, the concentrations were low and the risk was considered negligible, based on studies already published. With other insecticides, the death of entire colonies has already been recorded in the State of São Paulo”, says Domingues.
The researchers also calculated the displacement of the bees, using a methodology that indicates the distance they traveled by analyzing the dance they perform inside the hive. By these calculations, only a small percentage (4%) of the decoded dances indicated that the insects remained foraging within a radius of up to 500 meters from the colony, where the insecticide was applied. The majority (42.57%) reached distances from 1,500 to 2,000 meters, outside the product's range of action.
As a caveat, the researchers explain that this is a specific case and that for each crop it is necessary to know the pest life cycle in order to manage the application, as well as understand the spatial and temporal distribution of resources used in the landscape. In this way it is possible to reduce the risk of exposure of bees.
“In Brazil, this can be adapted to the most important crops at a more affordable cost, using ‘sentinel hives' equipped with automatic scales, for example, and determining the most relevant plant species used by bees through pollen and honey”, exemplifies Domingues.
“The use of these methods could be boosted with stronger regulation of pesticides used in Brazil. Unfortunately, last year there was the release of a huge amount of products that can be harmful to bees, when there are already less toxic and more easily absorbed products.” and even biological products”, laments the researcher.
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