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Connecting the dots: Dung beetles and pesticides

Gracie Johnson for Progressive Cattleman Published on 09 May 2018
beef cow in pasture with rub-on fly control product

Pesticides and dung beetles couldn’t seem more different when it comes to making a fly management plan, but they definitely are connected in the big picture of pest control.

We need dung beetles

Although it’s seemingly small and trivial to be concerned about a bug, dung beetles are unique when it comes to their fertilization services. Roger Moon, professor emeritus at the University of Minnesota, says, “The reason we worry about dung beetles is that they help accelerate the breakdown of cow dung on pasture. If there are lots of beetles and they get the dung into the soil, less of the nitrogen in the dung is evaporated – volatilized. So there’s a pasture fertilization service that dung beetles provide.”

Controlling flies

Dung beetle attraction to fresh manure is beneficial when it comes to fly management. It’s a preventative measure; with dung beetles using the manure to make brood balls, it takes away some flies’ opportunity to lay eggs and develop more flies.

Parasitic wasps similarly work toward preventing growth in fly population. The female parasitic wasp actually kills flies by laying her eggs in the larvae or pupae of the fly, allowing the wasp larvae to eat the developing fly as they grow, killing the fly in the process.

Unintended targets

Unfortunately, due to constant contact with manure, these insects can become unintended targets of pesticide residue.

Moon says, “It’s possible that residues of some insecticides, depending on when they’re applied and how they’re applied, could harm dung beetles and/or pollinators, and same with dewormers. … Some active ingredients are both dewormers and insecticides. So you have to be careful what active ingredients you’re talking about and the formulation before you can really know what’s likely to happen.”

Pesticide forms

Different formulations of pesticides can be used for fly control. Depending on the operation setup, there may be a variety of products on hand in different forms to get the best effect for cattle protection. Products can range from pour-ons, to eartags, to injectables and to oral larvicides.

Pour-ons are a common form of pesticide that is easy to use and effective in gaining pest control. However, if cattle are wet within six hours of administering the pour-on, it will wash off the hide. Pour-ons are also more likely to put residues of active ingredients in cattle feces. This is because pour-ons can be systemically absorbed in order to attack internal pests.

Injectable pesticides work similarly to pour-ons and are even more effective in gaining pest control since they are directly administered into the animal. But these also leave detectable amounts of residues in cattle feces, and it requires time and manual labor to gather cattle and administer the injection.

That’s what makes oral larvicides or “feed-throughs” an attractive alternative or addition to fly management programs. It’s a hands-off approach, with more focus given to cattle making the initial contact with products. Feed-through fly control can be set out by mineral tubs or even incorporated in feeds, so that cattle can consume it, allowing the pesticide to be mixed with the feces, thus preventing fly larvae from surviving. It only requires a little bit of larvicide to be effective, but it has to be consistently consumed in order for it to have impact on fly control. However, adult flies can still come from neighboring operations, so larvicides alone may not be dependable.

Product awareness is essential when it comes to balancing a good fly control program while encouraging beneficial insect growth.

Protection with control

Ellis Schrunk owns Sandy Spot Farm in Bartlett, Nebraska, and while observing his fields during last year’s grazing, he noticed a lack of beneficial insects. He says, “We used a pour-on pesticide on the cows when I started to notice a lack of dung beetles and had to wonder if it was because of the pour-on.”

Here are some practical steps that can help fly control management while also protecting nature’s free fertilizer service bugs.

Know the ingredients

Active ingredients used in pesticide products are the chemicals that are intended to either kill, control or repel a broad spectrum of pests or targeted pests. However, “If you have ivermectin, or any of the macrocyclic lactones active ingredients, which are moxidectin, ivermectin and doramectin,” Moon says, “these compounds can be applied topically or as oral larvicides, and in turn the residues can come out in the feces. If the residues are abundant enough and if used at the wrong time, they can hurt developing dung beetles; we know that’s true.”

Read the label

Labels on pesticide products address how much insecticide should be applied per animal for optimal results. It also includes an estimated time frame of how long it works, and some even give recommendations of time frames for when it’s appropriate to allow cattle out for grazing after application. The science has been done to formulate it; all that’s left to do is follow the instructions as closely as possible.

Plan ahead

For those grazing on BLM grounds or other conservation properties, following the time frames set by lessors is an important step in preventing chemical residues from inhibiting dung insect growth. Since most conservation properties and BLM grounds are considered public property, it’s important to maintain good public relations, especially as the public’s interest in beneficial organic organisms grow. Moon says, “The scientific literature is strong enough to say that some of these compounds can harm dung beetles, and if people who love dung beetles say, ‘OK, I don’t want to harm my dung beetles,’ there’s a work-around like treating before spring to clean up worms.”

As producers gear up for fly season, it pays to consider Mother Nature’s fertilizer bugs while organizing the fly control management plan for the year.  end mark

Gracie Johnson is a 2018 intern for Progressive Publishing.

PHOTO: Cattle rubbing on a fly control product in the Nebraska Sandhills. Photo by Lynn Jaynes.

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