10
Dec
Widely Used Insecticide Imidacloprid Negatively Impacts Soil Communities, Study Finds
(Beyond Pesticides, December 10, 2024) Scientists from the Engineering Research Center of Protection and Utilization of Plant Resources at Shenyang Agricultural University in China reveal adverse effects of imidacloprid on soil communities in a study published in Pesticide Biochemistry and Physiology. The researchers highlight risks to nematodes from imidacloprid exposure in maize soil, as well as potential resistance mechanisms that impact not only nematode populations but also overall soil health.
Maize, or corn, a productive crop grown worldwide, is a source of food and biofuel. In assessing the soil and species in maize fields after exposure to imidacloprid at various concentrations, the study researchers assess the impact of neonicotinoid insecticides on nontarget organisms and the health of soil communities. The assessment includes an evaluation of nematodes’ survival, growth, reproduction, and chemotaxis/locomotion behavior. With a statistical analysis of lipid and lipofuscin accumulation, acetylcholinesterase (an enzyme necessary for neurotransmission) activity, and gene expression levels, the study results show that imidacloprid induces:
- significantly reduced abundance and diversity of nematode species.
- negative effects on body length, reproduction, locomotion, lipid accumulation, lipofuscin accumulation, and acetylcholinesterase activity in Caenorhabditis elegans ( elegans).
- the upregulation of gpa-1, cyp-35a2, fat-2, fat-6, hsp-16.41, and hsp-16.2, along with the downregulation of ace-1, ace-2, and ace-3
- corresponding adaptive mechanisms and repellant behavior in nematodes.
The authors report, “[A]nalysis showed that the community richness index and community diversity index of soil nematodes in maize rhizospheric soil sprayed with imidacloprid were significantly lower than those from untreated soil. These results indicated that spraying with imidacloprid significantly reduced the number and diversity of soil nematodes in maize rhizospheric soil.â€
Also of note, the relative abundance of two bacteria-feeding nematodes within the genera Prodesmodora and Oscheius is lower in soil exposed to imidacloprid. “Both bacterial- and fungal-feeding nematodes contribute to the mineralization of soil nutrients such as nitrogen, thereby facilitating plant growth,†the researchers say. Differing soil nematode community compositions between treated and untreated soils highlight the impacts of pesticides on beneficial nontarget organism populations.
The study finds body length and body width of C. elegans decrease with increasing concentrations of imidacloprid, as well as significantly reduced brood sizes in individuals exposed to imidacloprid. Locomotion behavior, due to basic nervous system functions, for nematodes is assessed through three actions, body bends, head thrashes, and pharyngeal pumping. After 24 hours of exposure to imidacloprid, the researchers note that the frequencies of all three behaviors were suppressed, confirming neurotoxicity to nematode species. Imidacloprid additionally inhibits lipid accumulation and acetylcholinesterase activity in nematodes while it increases lipofuscin accumulation that leads to intestinal damage.
Assessing gene expression in nematodes provides insight into how pesticides cause epigenetic modifications upon exposure. Genes can also play a key role in resistance mechanisms. “A growing number of studies have highlighted the development of imidacloprid resistance in insects,†the authors state. “In this study, the major metabolites, imidacloprid-guanidine and imidacloprid-urea, appeared after 24 hours’ treatment with imidacloprid… Imidacloprid-urea has been shown to reduce the harm of imidacloprid to nematodes by about half. As to imidacloprid-guanidine, it is the intermediate pathway for the conversion of imidacloprid-urea, and imidacloprid-guanidine has been shown to have no insecticidal properties in previous reports, therefore we believe that C. elegans could convert imidacloprid to imidacloprid-guanidine and imidacloprid-urea to reduce the toxicity of imidacloprid.â€
In converting imidacloprid into its metabolites, nematodes show higher tolerance and experience less of the toxic effects. The enhanced expression of the cyp-35a2 gene, which is involved in resistance, as seen in C. elegans, also provides an effective defense against imidacloprid-induced damage. High expression of gpa-1 may also contribute to repelling imidacloprid. These results highlight how imidacloprid disrupts a series of physiological and biochemical indicators, as well as alters expression of genes associated with development, fat metabolism, and stress responses.
Impacts on soil biota following pesticide applications are well documented. Many nontarget organisms suffer negative impacts after exposure, such as with neonicotinoids and pollinators. While imidacloprid is primarily used to control sucking insects such as aphids, there is a wide body of science linking this pesticide to its effects on various beneficial nontarget organisms such as bees.
While impacts on nematodes are less studied, these organisms provide ecosystem services within the soil and act as an effective biological control. (See previous Daily News coverage here and here.) Healthy soil promotes biodiversity and supports numerous key ecosystem processes including decomposition and nutrient cycling.
“[T]he biodiversity present in soil makes a significant contribution to the agricultural productivity of the soil. Together with many other soil organisms, soil nematodes are crucial parts of the soil ecosystem,†the researchers share. “Nematodes, including the notorious plant-parasitic nematodes, are able to regulate the rhizospheric microbiota and drive soil microorganism community composition. Furthermore, nematode excrement has been found to contribute up to 19% of the soluble nitrogen in the soil. Therefore, their diverse ecological functions and intricate trophic positions make soil nematodes are good indicators of soil biodiversity.â€
Imidacloprid and numerous other pesticides threaten critical soil communities and the needed balance in food webs. Whether as a spray or seed coating agent, imidacloprid is absorbed by plants and transported to various tissues. Residues of imidacloprid are found in the plant body and in the soil, which expose many beneficial nontarget organisms.
As an alternative, organic agriculture eliminates the use of toxic petrochemical pesticides and synthetic fertilizers that harm the environment and all the organisms it supports. In prioritizing soil health, organic land management methods mitigate against the crises of health, biodiversity, and climate change.
Learn more about the benefits of organic here and here. Join the organic solution by Eating with a Conscience and growing your own food or buying organic products. Stay informed through Beyond Pesticides’ resources. The Pesticide-Induced Diseases Database (PIDD) provides scientific literature on public health effects of exposure to pesticides and the Gateway on Pesticide Hazards and Safe Pest Management catalogs information on specific chemicals. Join Beyond Pesticides as a member today to add your voice to the urgent movement to eliminate fossil fuel-based pesticide use.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Zhang, J. et al. (2024) Interaction between imidacloprid residues in maize rhizospheric soil and soil nematode community, Pesticide Biochemistry and Physiology. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0048357524004528.
