A class of insecticides called neonicotinoids have been shown to impact bees and other non-pest insects. A research group out of the University of Bern in Switzerland wanted to study how these insecticides impacted social insects as opposed to bees, particularly over extended periods of exposure. PhD student Daniel Schläppi, working under Prof. Peter Neumann studied garden ant colonies over a period of 64 weeks to see how their colonies were impacted by the neonicotinoid insecticides.

Garden ants have both queens (which can live as long as thirty years and lay the eggs for the colony) and worker ants (who collect food, care for the eggs, and otherwise do the work around the colony). Because of the long lifespan of queen ants, as high as 15 years, the researchers hypothesized that garden ants may be particularly susceptible to long-term exposure of insecticides in the soil.

To study any impacts of long-term exposure, the researchers collected 24 newly matured queen ants and their colonies and raised them in a lab with either no exposure, low exposure, or high exposure to the insecticide thiamethoxam over 64 weeks. They then analyzed the survival rates, weight, and population of queens and workers in each colony as well as the amount of insecticide and its break down products in the ants.

The researchers found that, roughly, queens were equally likely to survive and to have similar weights no matter what their insecticide exposure was. While all colonies had about the same number of workers at week 13, worker bees exposed to more insecticide had both tapered in number and weighed less by week 64. When ants’ bodies were tested for residues, more insecticide was found in worker ants than in queen ants. The researchers suggested that queen ants can detoxify the insecticide better than worker ants, but lay fewer eggs than their non-exposed counterparts due to the energy drain.

While this research did not look at the effect of colony survival long term, smaller ant colonies tend to struggle more both in conflicts with other colonies and also in resource gathering. Therefore, continued decreases in colony size over the ants’ lifespans could have significant effects. In the future, researchers recommend continuing to study the effect of pest-control chemicals on ants and other non-target insects over their entire lifecycles and, of course, keeping the results in mind when choosing chemicals to use for crop protection.

Managing Correspondent: Emily Kerr

Press Article: Alarming long-term effects of insecticides weaken ant colonies

Scientific Article: Long-term effects of neonicotinoid insecticides on ants

Image Credit: Magdalena Smyczek–Black Ants Fighting