29
Apr
Bats’ Voracious Appetite for Agricultural Pests and Mosquitoes Are a Part of Nature’s Balance
(Beyond Pesticides, April 29, 2020) The terrible reputation with which bats are commonly saddled — especially now, because of their association with the origins of the family of coronaviruses — is undeserved. These nocturnal insect vacuums are fascinating, flying mammals that are under-appreciated, not least for their performance of important services for ecosystems, and for human health and agriculture. Investigators from Israel’s Ben-Gurion University and the Section for Evolutionary Genomics at Copenhagen’s Natural History Museum recently published a study demonstrating that bats can be a mighty tool against pests that damage cotton crops. Bats’ pest control services — relatively invisible because they do their insect marauding at night when humans are not watching — represent an excellent, nontoxic, biological control for some agricultural pests, as well as for mosquitoes that may be human disease vectors. Advocates say that these services should be well considered before any decision to use toxic pesticides that can harm bats, as Beyond Pesticides has covered.
The study, “An appetite for pests: Synanthropic insectivorous bats exploit cotton pest irruptions and consume various deleterious arthropods,” was published in Molecular Ecology. [Note: “synanthropic” species are those plants or animals that live near, and benefit from, association with humans and the habitats people create around or in response to them.] The subject of the study is a small bat, Kuhl’s pipistrelle (Pipistrellus kuhlii), which roosts and forages in such habitats: urban, exurban, and agricultural areas. The research, undertaken in cotton fields in central Israel, looked at this bat’s consumption habits by studying trace DNA of its prey in the bat’s droppings.
The scientists were particularly interested in P. kuhlii’s consumption of a notorious cotton crop pest, the pink bollworm — a formidable threat in much of conventional cotton growing because it can easily develop resistance to the pesticides marketed for use with genetically modified cotton seeds. It seems that Kuhl’s pipistrelle loves the pink bollworm: as bollworm populations swelled, the bats preferred and ate more of them than of any other insect species. The scientists concluded that these bats exploit pink bollworm irruptions by opportunistic feeding, and that the bats provide “important pest suppression services.” Professor Carmi Korine, Ph.D., one of the study paper’s authors, notes: “We should be aware of the functional importance of common species of bats in urban environments for ecosystem functioning and human society. . . . particularly now, when bats are negatively and often unjustifiably stereotyped due to COVID-19.”
The study’s conclusions underscore the importance of bat species and their services. Bats are the only nocturnal insect predator in the U.S., and are one of two primary nocturnal pollinators (along with moths) — important roles for night-flowering plants and for farmers. The two species of brown bats (the “big” and the “little”) most common in the U.S. are voracious, consuming 3,000–7,000 insects per night. In some regions, these creatures also provide fertilization through deposits of their guano; notably, there is a thriving commercial fertilizer industry that uses guano as a primary ingredient.
As mentioned, bats consume mosquitoes that can carry diseases to humans, such as West Nile virus, Eastern equine encephalitis, Zika virus, malaria, dengue fever, yellow fever, and others. Many localities and states continue to use aerial pesticide spraying (“adulticiding”), as well as some biological controls and source reduction measures, not only in declared public health emergencies, but also and too often, for “nuisance control.” Pesticide use to control mosquito populations is misguided, at best, because of its harmful impacts on human health, ecosystems, and the very organisms that prey on mosquitoes, and because it is often ineffective. There are alternatives to spraying toxic pesticides for mosquito control.
A 2011 study in the journal Science estimates that bats provide annual pest control services to agricultural operations worth between $3.7 and $53 billion. Bats are also considered an “indicator species,” meaning that they interact with many elements of their ecosystems, and that their well-being is a barometer for the health of those ecosystems.
Bat populations in some regions are shrinking alarmingly due to myriad threats, including pesticides, habitat destruction, and white-nose syndrome (WNS), a fungal disease to which several cave-dwelling bat species are particularly susceptible. WNS first spread through bat populations in the eastern U.S. and Canada, but has now expanded as far as the West Coast. In some areas, bat species have lost 90% of their local populations to the disease. WNS causes bats to behave uncharacteristically — waking up more frequently during the winter, and flying during the day, and thus, using up their limited fat reserves too quickly, leaving them debilitated. Estimates of bat losses to WNS range from 5 to 7 million since the onset of the fungal disease in 2006.
Bats are also vulnerable to pesticide exposures through their dusky and nocturnal foraging for insects that may have been sprayed by pesticides or may have fed on pesticide-treated plants. Because bats are unusually long-lived for animals their size — lifespans range from 20 to 40 years — their bodies can accumulate pesticide residues over a long period, exacerbating adverse effects associated with those pesticides that can accumulate in fatty tissue. Also, during migrations or winter hibernation (when their fat stores are metabolized), bats’ consumption of large volumes of pesticide-contaminated insects can mean that these compounds may reach toxic levels in their brains — making them more susceptible to WNS. Bats also tend to have only one offspring each year, making them vulnerable to the population impacts of negative reproductive effects caused by pesticides, because low reproductive rates require high adult survival rates to avoid population declines.
Beyond Pesticides will continue to advocate for pollinator species, including bats. There are many ways that the public can support these inky and slightly chimerical creatures, and protect them from pesticides. Learn more at Beyond Pesticides’ pollinator protection page, Hedgerows for Biodiversity fact sheet, and alternatives to spraying page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources: https://www.israel21c.org/bats-arent-all-that-bad-just-ask-israeli-cotton-crops/ and https://onlinelibrary.wiley.com/doi/abs/10.1111/mec.15393
