Food safety protocols often pressure growers to remove natural habitat from their farms or to distance livestock from produce. The goal is to keep out any animals that can vector foodborne pathogens. After all, it takes only five to 10 E. coli 0157:H7 cells to infect humans.
Yet this could come at a cost of reduced biodiversity. Due to recent research I led as part of gaining my Ph.D. at Washington State University in the Journal of Applied Ecology, I encourage you to conserve dung beetles and soil bacteria on your farms. Why? They naturally suppress pathogenic Escherichia coli (E. coli).
The feces of wild and domesticated pigs have been known to contaminate produce in the field, leading to foodborne illnesses. Feral pigs pose a risk of spreading pathogens, as farmers cannot control where or when these large animals might show up.
So naturally growers worry about food safety. Many remove natural habitats from their farm fields to discourage visits by livestock or wildlife. The unintended result? Farmland is less hospitable to pollinators and other beneficial insects or birds.
How We Set Up the Study
We chose to focus on dung beetle activity. They bury feces below ground and make it difficult for pathogens to survive.
To study how this may aid food safety, we recruited 70 brassica growers along the U.S. West Coast from Southern California to Washington State.
We chose brassicas as our test crop because, much like leafy greens, they’re susceptible to fecal contamination due to their proximity to the ground. And there’s a high likelihood of humans consuming them without cooking.
I then drove a van full of pig feces to the farms, following the brassica growing season.
We used pig feces in two ways. It attracted dung beetles into our traps so we could sample the community. We also wanted to see how quickly the beetles would remove potential fecal contamination on farms.
One last detail I should note is we conducted the study at three types of farms:
- Farms integrating crops and livestock
Conventional Farms Attract Less Effective, Invasive Beetles
The organic and integrated crop-livestock farms attract a diverse range of dung beetle species that were most effective at keeping foodborne pathogens at bay.
At conventional fields, or those surrounded by more pastureland, a less effective and unintentionally introduced species (Onthophagus nuchicornis) outweighed the number of native dung beetles. This species likely thrives in the more simplified habitat.
“We found that organic farms generally fostered dung beetle species that removed the feces more rapidly than was seen on conventional farms,” says Professor William Snyder of Washington State University.
E. coli Reduced by More Than Half
Dung beetles likely kill harmful bacteria when they consume and bury the feces. Previous research also suggested that these beetles have antibiotic-like compounds on their body.
To validate these findings, we exposed the three most common species found in the field survey to pig feces contaminated with E. coli.
A seven–day laboratory experiment revealed that Onthophagus taurus and Onthophagus nuchicornis, both of which bury feces as part of their breeding behavior, reduced E. coli numbers by less than 90% and greater than 50%, respectively.
Should Growers Create Beetle Banks?
A 2006 study by Washington State University’s Renee Prasad and William Synder found that trying to boost beetles on your farm can be a mixed bag. Creating a habitat for beetles, also called a beetle bank, does indeed increase the number of beetles. However, they found that a large invasive species, P. melanarius, preyed on the native beetles.
“In the real world,” Snyder says, “strategies might fail for reasons hard to see in a petri dish or cage.”
Diverse Bacteria in Soil Kills E. coli
In addition to the benefits of dung beetles, we also found that organic and integrated crop-livestock farming encouraged higher biodiversity among soil bacteria. And our tests revealed the more diverse the bacteria, the more it decreased the survival of pathogens.
This pattern was driven by the higher amounts of organic material in the soil, characteristic of organic farming systems.
Flies Can Transfer E. coli
In our follow up study, published in the journal Biological Control, we tested the ability of dung beetles to reduce the amount of pathogenic E. coli that flies could transmit to produce.
To do this, we performed a lab study using the most common fly and beetle species from the aforementioned field survey. In experimental units including beetles, we found lower levels of E. coli on the flies themselves and, consequently, lower levels of the pathogen were transmitted to adjacent brassica seedlings.
These results suggest dung beetles and soil bacteria may improve the natural suppression of human pathogens on farms, both in the soil and on other potential arthropod vectors.
Encourage Diversity on Your Farm
Wildlife and livestock are often seen as something that endanger food safety, and they certainly can be risks, but our research shows that reducing on-farm biodiversity might be totally counterproductive. Nature has a clean-up crew of dung beetles and bacteria that quickly remove feces and the pathogens within them, it appears. So, it might be better to encourage these beneficial insects and microbes.
Read Our Journal Reports on the Studies
If you would like to learn more about our research, you can read our full study in these peer-review trade journals:
- Jones, Fu, Karp, Besser, Reganold, Tylianakis, Snyder. 2019. Organic farming promotes biotic resistance to food-borne human pathogens. Journal of Applied Ecology. 2019. 00:1–11.
- Jones, Wright, Smith, Headrick, Besser, Reganold, Crowder, Snyder. Organic farms conserve a dung beetle species capable of disrupting fly vectors of foodborne pathogens. Biological Control. 2019. 3:104020