California scientists find two ant baits trigger very different behaviour

A new study by University of California, Riverside researchers reveals that two common insecticides can cause Argentine ants to behave very differently after being introduced to a bait. The chemicals are thiamethoxam and boric acid, both of which eventually kill most of the worker ants. However, their effects on the colony are quite distinct.

When exposed to thiamethoxam, many Argentine ants became unusually active and started wandering outside their nests before eventually dying. The researchers believe this unusual movement might be related to how thiamethoxam affects the insects' nervous system. The chemical mimics the effects of nicotine on the insect nervous system, overstimulating it and causing paralysis. Thiamethoxam killed all the worker ants within about seven days.

In contrast, boric acid caused the affected ants to stop foraging and gather tightly inside the nest, particularly near sources of water. Boric acid killed about 90% of the worker ants within roughly two weeks. Some people favor boric acid because it's less toxic to non-target insects, but it's still harmful to ants.

The study also showed that killing worker ants doesn't necessarily mean the entire colony is gone. Both insecticides killed most of the workers, but the queen could still survive and produce a new brood, making the relief from a single bait treatment temporary. Additionally, the way ants share food could influence how much insecticide each ant receives, potentially extending the unusual roaming behavior in some cases. The researchers emphasize that Argentine ants are notoriously difficult to control.