Pest Infestation-Reducing Bats Dying from Pesticide Exposure
Researchers from the University of Tennessee tracked populations, eating habits and migration patterns of Brazilian bats (Tadarida brasiliensis), and compared them to the patterns of corn earworm moths (Helicoverpa zea) through multiple seasons.
They determined that the bats tracked and migrated with the moth infestations, and fed off of the moths where they gathered – among corn crops. The bats were found to migrate to moth infestations, dramatically reducing their populations. The evidence provided confirmation that bats are lethal predators of these and other pests that threaten our crops.
The researchers confirmed with their conclusion the importance of bats to preventing pest infestations on cropland and urban areas: “Our results support growing evidence for the role of generalist predators, and bats specifically, as agents for biological control and speak to the value of conserving indigenous generalist predators.”
At least 70% of bats are insect-eaters. The type of insect eaten depends greatly upon the species. There are over 1,200 species of bats. They will typically eat the insects known to infest that particular geographical region, but many also migrate with the insects as determined in the Tennessee research. Some bat colonies have been observed eating tens of thousands of pounds of insects each night.
Bats are dying by the millions
The problem, however, is that bat populations are being reduced in many areas, and researchers are suspecting the involvement of pesticides. This is concerning numerous bat and environmental experts, who have connected insect infestations to bat population reductions.
According to the Bat Conservation International, a group committed to the conservation of bats, more than 5.7 million (and possibly up to 6.7 million) bats have died from a disease called the White-nose Syndrome. The disease appears to be connected to a fungus, but is also related to immunosuppression among the bats.
The link to pesticides
The syndrome is strikingly similar to the bee’s colony collapse disorder, which many have attributed to a virus, but more recent research is connecting the disorder to pesticides. The research on CCD among bees has increasingly indicated that pesticides weaken the immune system, allowing the infection to take hold. Now this connection is also being made among bats.
Researchers from the State University of New York and the New York State Department of Health with the Department of Environmental Health Sciences released a study that illustrated that bats were accumulating toxic chemicals from pesticides and these were connected with their subsequent immunosuppression as well as hormone disruption. They found that little brown bats found diseased with the White-nose syndrome also had significantly high levels of several pesticide- and herbicide-related chemicals in their fat tissues. These included polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), organochlorine pesticides (OCPs which include DDT, chlordanes, HCB, and HCH). They found the highest levels of PCBs and PBDE concentrations in the bat fatty tissues were related to bats from regions with cropland spraying of pesticides.
The connection between declining bat populations and pesticides is also beginning to unfold among other research. Researchers from Germany’s University of Koblenz-Landau tested bats and bat activity among apple orchards before and after the orchards had been sprayed with pesticides. They found that bats were increasingly retaining pesticide residues and this was decreasing their activities and populations among the orchards.
Their research concluded a connection between pesticides and bat population loss: “The results emphasize the importance of adequately evaluating the risks of pesticides to bats, which, compared to other mammals, are potentially more sensitive due to their ecological traits.”
Bat populations are slow to rebound
One of most bat’s traits is that they typically will have only one offspring, meaning that re-population of bats is a long and difficult process.
Bat experts have calculated that the loss of 5.7 million bats converts to nearly 4 billion pounds of additional insects. According to Bat Conservation International’s Executive Director Nina Fascione, losses in bat populations indicate a critical issue to come, as “the environmental and economic costs will be enormous.”
The loss of our bat populations will not only produce greater incidence of pest infestations. Many species of bats are important pollinators for many types of fruits. These species of bats prefer eating pollen to eating the insects that attack plants. The bats go from flower to flower eating pollen. Some of that pollen gets stuck in their fir, getting carried to other flowers. This effective pollination method is very similar to bees who transfer the sticky pollen from plant to plant as they harvest different flowers.
Most bat experts agree that bats are still somewhat mysterious due to their nocturnal activities. What is we are slowing realizing – and possibly too late – is that our widespread use of chemical pesticides is backfiring. Not only are we becoming poisoned by them: Those beneficial species that work alongside our food crops to assure their pollination and pest control are also becoming poisoned, and this may well threaten the future of our food supply.
McCracken GF, Westbrook JK, Brown VA, Eldridge M, Federico P, Kunz TH. Bats track and exploit changes in insect pest populations. PLoS One.
Stahlschmidt P, Brühl CA. Bats at risk? Bat activity and insecticide residue analysis of food items in an apple orchard. Environ Toxicol Chem. 2012 Jul;31(7):1556-63.
Kannan K, Yun SH, Rudd RJ, Behr M. High concentrations of persistent organic pollutants including PCBs, DDT, PBDEs and PFOS in little brown bats with white-nose syndrome in New York, USA. Chemosphere. 2010 Jul;80(6):613-8.
Bat Conservation International. New WNS death toll confirms worst fears. Press Release. 2011. January 11.