Simultaneous exposure to low doses of pesticides (insecticides, fungicides and similar) commonly used in agriculture and gardening, and to adjuvants found in some of these chemicals (to enhance or model their action) damages the olfactory ability of honey bees. (Apis mellifera), alters the communication capacity in individuals of this social species and, consequently, reduces their reproductive capacity and general health. These are some of the most notable results of a new study on bee decline led by experts from the Carl R. Woese Institute for Genomic Biology (Illinois IGB) at the University of Illinois (United States).
Specifically, the authors of this study indicate that they have verified that "the fungicide Tilt and the insecticide Altacor, with the active ingredients propiconazole and chlorantraniliprole, respectively, together and in combination with the organosiliconic surfactant adjuvant Dyne-Amic altered the olfactory responses of the worker bees to the brood pheromone and the alarm pheromone 2-heptanone". "This finding suggests that these commonly used pesticides may interfere with bee communication and reproductive systems that depend on olfactory signals," the authors indicate in the summary of their study, published in the journal Scientific Reports.
"Honey bees live in dynamic communities and constantly communicate with each other using chemical substances that serve as social signals," recalls Anayan Sen in a dissemination article on the new study published on the Illinois IGB website. For example, nurse bees, which are responsible for caring for larvae that eventually become queen and worker bees, constantly monitor the larvae in the dark using pheromones. The larvae emit breeding pheromones to indicate that they need food. There are also alarm pheromones that worker bees produce to warn other bees of danger. If these signals are reduced or not perceived properly, the colony may not thrive.
The increase in health problems in bee colonies has been studied for several decades and in recent years an increase in cases of mass death of these insects has been detected. One of the factors that have generated concern are insecticides, which not only cause death in direct exposure, but also cause significant damage in low doses. One of the data now under study is the effect of combination with other chemicals, for example, mixtures of pesticides and adjuvants that can be unexpectedly toxic to bees.
"For many years, it was assumed that fungicides do not have an adverse impact on insects because they are designed to attack fungi," explains May Berenbaum (GEGC/IGOH), professor of entomology at this university. "Surprisingly, in addition to insecticides, fungicides also have an adverse effect on bees and the combination of both can disrupt colony function."
For more than a decade, reports from almond fields, where two-thirds of American bees are transported each year when the trees are in bloom, involved spray pesticide mixtures. In particular, the problem lies in the use of supposedly inactive chemicals called adjuvants, which increase the “stickiness” of the insecticide so that it remains on the plants.
Because adjuvants have long been considered biologically benign, they are not subject to the same level of safety testing as other insecticidal agents. "Recently, researchers have shown that adjuvants alone or when used in combination with fungicides and insecticides are toxic to bees," explains Berenbaum in statements posted on the website of his research institute.
To understand how the combinations affect nurse bees, the researchers tested their effect on the olfactory system of honey bees using the adjuvant Dyne-Amic, the fungicide Tilt, and the insecticide Altacor.
The researchers divided the bees into four groups of ten bees and for a week exposed them to untreated commercial pollen or pollen that had been treated with Dyne-Amic, Tilt and Altacor, or all three together. The bees were then anesthetized on ice and one antenna was carefully removed from each bee. The researchers then exposed the antenna to chemical mimics of breeding and alarm pheromones and recorded the antenna's response using a technique called electroantennography.
Using this method, Ling-Hsiu Liao, a research scientist, and Wen-Yen Wu, a graduate student, in Berenbaum's lab, found that when nurse bees consumed pollen contaminated by the three chemicals, their responses to some pheromones breeding and alarm pheromones were altered. Their finding suggests that these commonly used pesticides can interfere with bee communication, says the University of Illinois. The study fails to discover how this interaction occurs and those responsible say they will study new substances to try to understand the origin and extent of these negative effects on the health of bees.
