Environment: Pesticides may be at the root of bee, bat and amphibian die-offs

Suppressed immune systems making insect-eating species more susceptible to different pathogens

Two years ago, this species of bee vanished from local flowerbeds in Frisco, Colorado.

By Bob Berwyn

FRISCO — Waves of emerging wildlife diseases that are killing huge numbers of insect-eating animals could all be linked to the use of a new class of pesticides, according to a study recently published in the Journal of Environmental Immunology and Toxicology.

Neonicotinoids and related pesticides may be suppressing the immune system of bees, bats and even amphibians, making them much more susceptible to parasites, viruses and fungal infections, the researchers found after comparing geographical patterns of emerging diseases with the use of neonicotinoids.

Insects feeding on the pollen and nectar of crops treated with the pesticides absorb the chemicals and the poison is subsequently passed on to animals higher up the food chain that prey on those bugs, the scientists hypothesized, citing evidence of deviation from normal pathogen-host relationships.

If it sounds familiar, it should — DDT had a similar cascading ecosystem effect, and the impacts from the “new and improved” pesticides could be even more devastating and costly, with the loss of bats and bees hitting the agricultural sector especially hard.

To explore the possible link between the pesticides and the catastrophic decline of bees, bats and amphibians, the scientists look back a couple of decades, finding that disease outbreaks started in countries and regions where systemic insecticides were used for the first time.

For example, the same year a pesticide called imidacloprid was licensed for use in Europe, beekeepers in France saw the sudden collapse of numerous beehives, as the worker bees flew off and never returned, leaving the queen and immature workers to die.

In their report, the scientists wrote: “The French beekeepers soon believed they knew the reason; a brand-new insecticide called Gaucho® with imidacloprid as active ingredient was being applied to sunflowers for the first time.”

More evidence comes from research showing immune suppression in bees and fish caused by neonicotinoids. Those studies have helped researchers understand the sub-lethal impact of these insecticides not only on these organisms, but probably on other wildlife affected by emerging infectious diseases.

When they started looking at the spread of the chytrid fungus that’s killing amphibians, they found a spatial relationship between applications of pesticides in California’s Central Valley and the subsequent die-off of frogs in Sierra Nevada ponds.

Other studies suggest that neonicotinoids persist in the environment for years, and signs of widespread contamination of bees in foraging areas: “Residues were also found in dandelions (Taraxacum spp.) foraged by bees; in dead bees collected near hive entrances and in pollen collected by bees and stored in the hive.”

The study found there is clear evidence showing that neonicotinoids suppress immunity in bees and fish. But so far, there is only circumstantial evidence for a link between the pesticides and the pathogen epidemics that are affecting amphibians, bats and insectivorous birds around the world.

“The appearance of such epidemics in places where systemic insecticides had been used in large quantities in previous years is, however, far from coincidental. At the root of the problem lies a lack of data on the widespread and insidious contamination of these new chemicals,” they wrote.

Understanding the impacts of the new class of systemic pesticides is challenging because monitoring hasn’t kept pace. In some cases scientists who suspected the possibility of chemical pollution as a factor in species die-offs are working on pesticide data (and water quality measurements) that are 20 years out of date.

“This article is a wake-up call to the world authorities, environmental protection agencies and scientists to monitor thoroughly the waters and study the overall implications of systemic insecticides from a new perspective; that of human health and global biodiversity,” the study concluded.

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