Even very low concentrations of pesticides can disrupt the microbiome of aquatic invertebrate larvae, thereby affecting their health and resilience to stressors. This is the conclusion of a new study by researchers from the Faculty of Science at Palacký University and the University of Ostrava, which focused on dragonfly larvae.
The results of the study, titled Trace amounts of insecticide, herbicide, and their combination disrupt the bacterial and fungal microbiome of a nontarget aquatic invertebrate, were published in the prestigious journal Environmental Pollution.
The researchers monitored the effects of two commonly used pesticides on the larvae of the common darter (Sympetrum vulgatum). They focused on the herbicide metazachlor, applied primarily in rapeseed fields against common weeds, and on the insecticide etofenprox, which is used against insect pests. Using molecular methods, they analyzed the larvae’s microbiome—a collection of tiny microorganisms consisting primarily of bacteria, fungi, viruses, and other microscopic life forms—and found that the insecticide caused the most significant changes. It reduced the diversity of the microbiome, altered the composition of microbial communities, and disrupted the relationships between individual microorganisms. The combination of both substances did not have a stronger effect than the insecticide alone, but it did influence the way microbial communities form.
Even low concentrations of pesticides disrupt microbial balance
“A key finding is that changes in the bacterial and fungal microbiome of the larvae were observed even at extremely low concentrations of pesticides, which were well below levels commonly found in aquatic environments. This concentration can be imagined as a single drop of the substance in a volume of water equivalent to roughly one hundred thousand Olympic-sized swimming pools. The results thus show that even minute amounts of these substances can disrupt sensitive biological processes,” said the study’s lead author, Hana Šigutová, from the Department of Zoology at the Faculty of Science, UP.
“A key finding is that changes in the bacterial and fungal microbiome of the larvae were observed even at extremely low pesticide concentrations, which were well below the levels commonly found in aquatic environments.” Hana Šigutová
According to the scientists, pesticides can also suppress potentially beneficial microorganisms and promote the growth of species associated with disease, as well as with the breakdown of foreign chemical substances. “Because the microbiome can significantly influence the resilience, health, and ability of its hosts to cope with stressors, trace exposure to pesticides in non-target aquatic organisms represents a serious problem that is still overlooked,” added study co-author Petr Pyszko from the Department of Biology and Ecology at the Faculty of Science, University of Ostrava.
Natural environments enhance organism resilience
The research also showed that a naturally formed microbiome can play an important role in host resilience. Larvae collected from the wild had a richer microbiome and greater diversity of microbial communities than individuals reared under laboratory conditions and exhibited higher resistance to pesticides. According to the authors, this suggests that natural microbial colonization may help organisms better cope with environmental stress.
“For a more accurate assessment of ecological risks, it is therefore necessary to monitor not only direct toxic effects but also subtle changes in microbial communities, including the fungal component, which remains largely unexplored,” concluded Hana Šigutová.