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Daily News Blog

16
Jul

Health and Behavioral Development of Beneficial Black Garden Ants Stunted by Low Levels of Pesticide Exposure in Soils

(Beyond Pesticides, July 16, 2020) Long-term exposure to sublethal (low-level) concentrations of the neonicotinoid in soil negatively affects the health and behavioral development of black garden ants (Lasius niger) colonies, according to a study published in Communications Biology by scientists at the University of Bern, Switzerland. Ants are one of the most biologically significant insects in the soil ecosystem, acting as ecosystem engineers. Their burrowing behavior aerates the soil, allowing oxygen and water to penetrate down to plant roots. Additionally, ants increase soil nutrient levels by importing and accumulating organic material like food and feces, thus enhancing nutrient cycling.

Like many other insects, ants are unfortunate victims of the global insect apocalypse or population decline, and much research attributes the recent decline to several, including pesticide exposureBroad-spectrum pesticides, like neonicotinoids, indiscriminately kill pests and nontarget organisms alike, as their ubiquitous use contaminates soils, even in untreated areas. This study highlights the necessity of rethinking chemical pest management, developing sustainable agricultural practices that reduce the use of agrochemicals, like pesticides, to prevent permanent environmental ecosystem damage. Researchers in the study note, “To prevent irreparable damages to functioning ecosystems, [we] suggest to either fully incorporate long-term effects in risk assessment schemes, or to make a shift in plant protection strategies…[thus applying] the precautionary principle when making policy decisions.”

The sublethal effects of neonicotinoid insecticides on nontarget organisms are evident. Research shows long-term pesticide exposure on some social insects with long-living queens (e.g., bees) impacts foraging behavior, learning, orientation, memory abilities, immune functions, fertility, colony growth, and reproduction. A majority of studies detailing the sublethal effects of pesticides focus on pollinators due to their economic and environmental importance. However, there is a lack of data to show how pesticide exposure at low concentration affects soil-dwelling invertebrates, like ants, long-term. Soil ecosystems are of great economic and ecological importance, housing invertebrates which cycle and decompose organic nutrients for agriculture. Soil-dwelling insects are also essential biological indicators of soil health and quality. This study uses data collected at the University of Bern in cooperation with Agroscope and the University of Neuchâtel to investigate the long-term effects pesticide exposure has on black garden ants, undetectable during the first year of colony development. The study’s researchers state, “To fully understand the threat of toxic substances in risk assessments, long-term studies [require research to cover] full [organism] life-cycles to determine the ecological risk, especially for long-lived organisms like social insect colonies.”

The researchers examine laboratory-reared colonies of black garden ants, born from field-captured ant queens, after exposure to field-realistic (sublethal) concentrations of thiamethoxam. Scientists exposed gynes (the primary reproductive female class of social insects destined to become queens) of L. niger to this commonly applied agricultural pesticide. Thiamethoxam’s ability to bind to nicotinic acetylcholine receptors is 10,000-fold less potent than other neonicotinoids, including its clothianidin metabolite, making the insecticide an excellent candidate to test the effects of low-level exposure. To assess the potential chronic effects of pesticide exposure on colony development, researchers monitored ant colonies from colony establishment and first-year overwintering (hibernation) to second-year overwintering, for 64 weeks. Additional tests performed on the queen and worker ants analyze residue levels of thiamethoxam and clothianidin to measure uptake and detoxification of these neonicotinoids among the different insect classes.

According to the study, chronic exposure to sublethal concentration of thiamethoxam results in reduced ant colony size, propagating fewer worker ants and larvae during the second overwintering. The analysis of thiamethoxam and clothianidin residues indicates that ant queens have better detoxification mechanisms than workers. However, additional evidence finds that the superior detoxification may compromise the queens’ reproductive fitness. Lead author of the study, Daniel Schläppi, PhD, at the Institute of Bee Health of the University of Bern, states, “With our study we show that ants, which play a very important roles in our ecosystems and provide valuable ecosystem services such as natural pest control, are negatively affected by neonicotinoids too.”

Over the past 20 years, neonicotinoids became the most used insecticide in the global market, surpassing sales of the four major chemical classes of insecticides (organophosphates, carbamates, phenyl-pyrazoles, and pyrethroids). These systemic agricultural insecticides resemble nicotine and affect the central nervous system of insects, resulting in paralysis and death. Chemical exposure from water-source, food, and soil contamination can cause harmful to nontarget species, like pollinators and aquatic organisms. A 2015 study shows that soybean seeds coated with thiamethoxam did not adversely affect insect pests (slugs). Instead, the insecticide bioaccumulated in the pest and translocated to the nontarget insect predator (beetle) via ingestion. This translocation of thiamethoxam killed more than 60% of the insect predators, which caused crop loss as the decline in beneficial insect predators prompted an increase in pest populations. Furthermore, research finds that seeds coated with neonicotinoids are high toxicity to songbirds who confuse seeds for grit, which they consume for digestion. In addition to insecticides, herbicides also impact ecosystem biodiversity, especially in soils. Herbicides can devastate habitats adjacent to agriculture that are important to organisms for foraging, reproduction, and shelter. Alas, current risk assessment methods for pesticides are insufficient as assessment procedures fail to account for the sublethal effects of pesticides.  With the loss of a quarter of the global insect population and over three billion birds in the U.S over the last four decades, action is needed to mitigate our anthropogenic impact on essential ecosystem organisms.

This study is one of the few of its kind to investigate the potential impacts long-term, sublethal exposure on soil-dwelling invertebrates, like black garden ants. In addition to pesticide exposure routes from direct pesticide application and indirect food ingestion, residue in soils expose black garden ants to pesticides. Researchers consider black garden ants sedentary since colonies are usually immobile in their soil habitats. This sedentary lifestyle exacerbates chronic pesticide exposure as these residues can accumulate in the soil over decades. Since black garden ants have a long lifespan, with the queens living up to 30 years, it is vital to understand how pesticide exposure impacts these organisms.

Ants are eusocial insects that perform essential terrestrial ecosystem functions and require a colony of ample size to do so. Although the impact of neonicotinoid exposure varies among worker ants and queens, the decline in colony size from this exposure is most critical. Colony size indicates colony fitness, and ant colonies in poor health jeopardize regular ecosystem function. The number of worker ants is an integral part of ant colony fitness/success, and the study outcomes observe effects that threaten colony survival. The study’s researchers conclude, “This is an exemplary study showing how negative effects of an environmental contaminant only become visible after long[-term] monitoring, but with potentially far-reaching consequences. [We] stress the importance [of including] ants as model organisms and to fully incorporate long-term effects in future risk assessment schemes for more sustainable agriculture.”

Ants are ecosystem engineers that aid in maintaining normal ecosystem function and interaction, even outside of the soil environment. The data in this study has implications for soil-dwelling insect species, like ants, as chronic, low-level exposure to pesticide residue in soil habitats weakens soil health and productivity. More than ever, individuals must connect with their local, state, and federal elected officials to demand that we must protect insect populations. Now, grassroots advocacy groups in Connecticut, and Maryland, in addition to dozens of local groups, collaborate to create lasting positive changes to pollinator protection policies. Solutions like regenerative organic agriculture and organic land management curtail the need for toxic pesticide use as these practices warrant similar or better results than chemical-intensive ones. Learn more about the science and resources behind pesticides’ pollinator impact and take action against the use of pesticides. To find out more about what you can do to protect insects like ants that indirectly, and bees that directly pollinate, check out information on pollinator-friendly landscapespollinator-friendly seeds.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Sources: University of Bern, Communication Biology

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