Dung Beetles Combat Flies; Insecticide Overuse Harms Beetles

By Krisy Gashler

Insecticides added to cattle feed to combat flies “significantly lower” populations of dung beetles, which control flies naturally, new research finds.

Anyone who has walked through a barn or cattle pasture in the summer knows that flies are a nuisance and even a health hazard. Face flies can spread diseases like pink eye to cattle, and horn flies  biting flies that live on cows and take up to 20 blood meals per day  in large enough numbers can impact animals’ health and growth. But insecticides frequently used to combat these pests may actually be reinforcing the problem by killing dung beetles, which naturally control flies, and potentially harming other beneficial insects.

Researchers with the Cornell Integrated Pest Management program have been working in collaboration with farms across New York state to understand how feed-through pesticides – insecticides added to cattle feed to kill flies – impact dung beetle populations. The researchers are also sharing alternative strategies to control pest species, such as using walk-through fly traps, providing shelter, and recruiting poultry to eat fly larvae. 

“These flies can cause major problems for herds. If you’re raising steers, you want them to gain weight quickly, and the annoyance, injury and disease that flies can cause in large numbers can affect the animals,” said Ken Wise, livestock coordinator for Cornell Integrated Pest Management (IPM). “However, the broad-spectrum use of any insecticide is not an integrated approach to controlling flies. I know it’s a pain to do, but if you can estimate the number of flies on your cows and treat the animals only when they need it, you’re going to have a lot less insecticide in the environment.”

Feed-through insecticides harm dung beetles, don’t control face flies

Both flies and dung beetles lay their eggs in manure pats. Larvae eat the manure and then hatch as fully-grown insects. Dung beetles control flies by competing for the same manure for food and shelter. Other species of beneficial beetles that inhabit manure include predators such as rove beetles, hister beetles and water scavenger beetles, which also eat fly larvae. And beetles’ benefits go beyond fly control: when they create tunnels in manure pats and in the soil beneath them, they help break down waste more quickly and recycle nutrients back into the soil, helping to increase soil health and fertility.