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Protecting Grassland Ecosystems from Insecticides

By Scott Black on 2 September 2021
Scott Black

This article originally appeared in the fall 2020 edition of Xerces’ magazine, Wings. Click to view the full spring 2021 issue.

It was as a kid—on vacation with my family in the Pine Ridge region of northwestern Nebraska—that I first really noticed grasshoppers. I was already interested in anything that crawled, walked, or flew, but where I lived, in Omaha, I rarely encountered grasshoppers. The state park we were visiting, though, was a mix of ponderosa pine and prairie habitats, and as I walked through the tall grass I was amazed at the number of grasshoppers that launched themselves into the air or scurried away from my approach. Of course, I had to catch some for a closer look! It was cool to see that they came in different sizes and colors—green and brown, with delicate markings in black and patches of red or blue—and I was intrigued to find that some had wings (usually boldly patterned and brightly colored) and some did not.

 

A close up photo of a young grasshopper on red soil. The grasshopper is sitting facing to the left with its large hind legs folded against its body. It is pale brown with dark speckles, except for the inside of it's hind lags which are bright blue and yellow.
Many grasshoppers reveal bold markings or bright colors when they leap or fly. This grasshopper nymph has yet to develop wings, but already has a touch of blue on its legs. (Photo © Bryan E. Reynolds.)

 

At the time, I did not know much about insect development and didn’t understand that the ones without wings were juveniles. Actually, as I subsequently learned, they did have wings, but they were not yet fully developed. Grasshoppers are among the groups of insects that undergo incomplete metamorphosis, also called hemimetabolous development. Such insects emerge from eggs into nymphs (referred to as larvae by some entomologists) that look like the adults except for their lack of fully developed wings. They pass through several nymphal stages (instars) as they grow, before their final molt into the winged adult form. (In contrast, butterflies, bees, beetles, flies, and many other insects undergo complete or holometabolous metamorphosis, in which the immature stages look nothing at all like the adults.)

There are just under seven hundred species of grasshoppers in North America and about eleven thousand species worldwide. In North America only a small number, ten to fifteen species, are actually pests—and then only under certain conditions.

Most grasshopper species play a central role in food webs, both as consumers and as prey. Herbivory by grasshoppers is an essential ecosystem function and speeds up the flow of energy and cycling of nutrients from plants. Dead plants take a long time to decay and return their nutrients to the soil, but both the grasshoppers’ fecal pellets and the plant clippings they drop when feeding are more quickly broken down, which aids nutrient recycling.

 

A young burrowing owl runs across the ground with a green grasshopper in its bill. The owls feathers are fuffy. They are brown on its back and top of heard and white on its belly and chest. Its face is brown with horizontal stripes of white across its chin and forehead and it has striking yellow eyes that have a black center.
Among the many birds that rely on grasshoppers for a major part of their diet are burrowing owls, which as fledglings hunt and eat them. (Photo: Wendy Miller, Flickr [CC BY-NC-ND 2.0].)

 

Grasshoppers are a vital part of the diet of dozens of species of birds, small mammals, reptiles, and amphibians as well as spiders, robber flies, and other invertebrates. These insects make up 30 to 90 percent of the diet of grassland birds. For instance, more than 70 percent of the food that chestnut-collared longspurs feed to their nestlings are grasshoppers. Burrowing owls benefit from grasshoppers; although the adults usually feed small mammals to their young, when the young leave their burrows they capture large numbers of grasshoppers and other insects. Even such large mammals as coyotes prey on grass hoppers, and grasshoppers are eaten by people of many cultures.

Some grasshopper species are beneficial in that they help control unwanted vegetation. Turnbull’s grasshopper (Aeoloplides turnbulli) is also called the Russian thistle grasshopper because it prefers Russian thistle—tumbleweed—and other weedy members of the goosefoot family.

Although grasshoppers are vital to the ecosystems where they live, some species can at certain times become pests, particularly if they move into areas where people are growing crops. Because of their pest potential in western grasslands, the U. S. Department of Agriculture’s Animal Plant Health Inspection Service (APHIS) maintains a program to control grasshoppers and their close relative, the Mormon cricket (Anabrus simplex). In many years, APHIS and other federal and state agencies apply pesticides across hundreds of thousands of acres of both public and private lands in an effort to control these native insects. These toxic chemicals can be devastating to non-pest grass hopper species and to a great many other important insects, including bees and butterflies.

 

In this photo we look up at a small hill as a red plane flies overhead and away from where we stand. The hillside is covered in pink flowers. The plane has a trail of pesticide mist released from its wings.
Under the right conditions a few species of grasshopper can become pests, particularly when large populations occur in areas of grazing or crops. Both federal and state agencies apply pesticides to control them. (Photo: Anson Eaglin, USDA APHIS [CC BY-ND 2.0].)

 

In fact, it was an APHIS proposal that led to grasshoppers again coming into focus for me in my early days at Xerces. The agency had plans to spray insecticides on up to twenty million acres of mostly public lands in Idaho. Xerces joined with the Idaho Conservation League and other groups in suing APHIS. I provided an expert declaration on the potential impact of this spraying on pollinators and, because APHIS’s initial proposal allowed spraying directly over some streams, on the major impact this could have on aquatic invertebrates. Ultimately, we resolved the lawsuit with an agreement that allowed APHIS to use only pelleted carbaryl bait, and that enforced buffers along all streams in the area, prohibiting applications adjacent to these waterways. APHIS was also required to limit application in proximity to areas with endangered species such as the Bruneau hot springsnail (Pyrgulopsis bruneauensis). Because of our efforts, bait was applied to just over twenty thousand acres, a tiny fraction of the area in the original plans.

While a wide variety of insecticides have been used to suppress grasshopper populations over the years, currently APHIS relies mostly on an insect growth regulator (diflubenzuron) and continues to use bait laced with carbaryl. Applied both on the ground and by air, these chemicals can harm a broad assortment of insects and other invertebrates. Aerial applications of diflubenzuron are especially concerning because of the potential of this insecticide to drift, sometimes over long distances.

 

A close up of a grasshopper sitting on a green leaf. The grasshopper is facing to the right, with its wings closed over its back. It is a pale greenish brown color and has black markings.
The differential grasshopper can be found in weedy places, including in vacant lots and urban greenspaces. It is one of a few species that can be a pest. (Photo © Bryan E. Reynolds.)

 

Diflubenzuron prevents the formation of chitin, an important component of an insect’s exoskeleton, interrupting its normal development. The chemical is lethal, even at extremely small quantities, to most insects in their larval stage. Butterflies, moths, bees, and beetles can all be affected, as can many aquatic insects that spend most of their life cycle as larvae. Mayflies, for instance, are adults out of the water for just a brief period, from less than a day to a few weeks; they spend the rest of their lives (sometimes more than a year) as larvae in streams and rivers. If drift from diflubenzuron enters these waters, it can disrupt the development of or kill mayflies and many other aquatic insects, as well as crustaceans, snails, and freshwater mussels.

Carbaryl inhibits the action of the enzyme acetylcholinesterase, which is an essential component of the nervous systems of insects, birds, fish, and mammals. It is known to be extremely toxic for terrestrial invertebrates (including butterflies), aquatic invertebrates, and fish. APHIS recently approved the use of a relatively new insecticide, chlorantraniliprole, which leads to paralysis by changing how muscles use calcium, and is considered to be of low toxicity to honey bees—although there is some conflicting evidence as to its degree of toxicity, and we are uneasy about its potential impact based on results from toxicological tests on bumble bees and butterflies. In the western United States, where populations of the western bumble bee have declined and those of the monarch butterfly have plummeted, the expanding use of chlorantraniliprole is of major concern.

 

A close up of a grasshopper sitting on a yellow flower. The grasshopper is facing to the left, with its wings closed over its back. It is brown and has black markings. The last sections of its hind legs are green-blue in color.
Found in most parts of the United States and southern Canada, the two-striped grasshopper feeds on both grasses and broadleaf plants. (Photo © Bryan E. Reynolds.)

 

The use of any of these chemicals to control native insects over wide areas should be a worry to all of us, as they can adversely affect a broad range of non-target species that are food for wildlife, pollinate wildflowers, and help control the very “pests” that the chemicals are intended to suppress. Many natural enemies that normally regulate grass hopper populations are vulnerable to these insecticides, and disruption of their populations could result in outbreaks that are worse in decades to come.

Over the years, Xerces has commented on treatment programs on public lands in many western states. In many cases, though, this is a difficult issue to work on, because grasshopper outbreaks are cyclical and geographically varied, which means that APHIS control programs are as well. Pesticide treatments may occur in Montana one year, and in Utah or Wyoming the next. On top of this, APHIS makes it difficult to track where it is proposing to use pesticides and where it has actually applied them. Our recent requests to APHIS for maps of its planned applications have met with resistance.

 

A view of the open treeless rangelands of Eastern Oregon. We are looking down a small valley that curves gently to the left. A creek flows along it, marked by grren grass that contrasts with the browner vegetation of the rangeland. Black cattle graze the green grass. In the distance mountains rise to the clouds.
The Xerces Society’s advocacy against extensive spraying of public lands to control grasshoppers has prevented streams from being sprayed and protected rangeland pollinators. (Photo: Greg Shine / BLM [CC BY 2.0].)

 

Thanks to the support of Xerces members and private foundations, we are now fortunate to have dedicated staffing to help educate the public and land managers about this issue and to advocate for protection of public rangelands and the wildlife they support. As with all of our efforts, we use a holistic conservation-science approach. We are working to understand grasshopper ecology and the potential risks of currently used insecticides, as well as which grasshopper-management methods minimize impacts to non-target species. We are also investigating possible options for managing grass hoppers with minimal or no pesticide use. Studies suggest that overgrazing may exacerbate grasshopper outbreaks, and leading researchers have questioned whether impacts on grasshoppers’ natural enemies mean that periodic insecticide treatments actually impede control. Some researchers have pointed out that improving range conditions and increasing perennial grass and forb cover in western rangelands could boost the numbers of highly insectivorous birds, such as longspurs, meadowlarks, and grasshopper sparrows, that help to regulate grasshopper densities.

Xerces also effectively uses outreach and technical assistance to help restore and manage habitat with insects in mind. In the near future we will be presenting webinars and workshops to land managers and landowners, and working directly with agencies and individuals that want to explore alternatives to the current practice of large-scale use of toxic insecticides to suppress grasshoppers. We will also continue to advocate for more tolerance of these native insects on public lands. Allowing intensive insecticide use over hundreds of thousands of acres of public and private lands across the west with minimal oversight or transparency is just not acceptable, and we will work with partners to seek legal and policy remedies.

When I was a kid, I found grasshoppers to be both engaging and beautiful. These animals may not excite and inspire people the way that bees and butterflies do, but they are equally important. The control measures currently used are blunt instruments that can harm many of our other important insects on which humans depend for such ecosystem services as pollination, as well as the animals that rely on those insects for sustenance. Grasshoppers and their habitats deserve to be protected, and we are committed to continuing our efforts on their behalf.

 

A close up of a grasshopper sitting on a brown twig. The grasshopper is facing to the left, with its wings closed over its back. It is brown.
The green-striped grasshopper has two color forms, one that is largely green and another that is brown, shown here. (Photo © Bryan E. Reynolds.)

 

Further Reading

Read the entire spring 2021 issue of Wings.

Learn more about efforts to change grasshopper spraying campaigns on our blog

Read about how Great Plains rangelands are important habitat for pollinators

Learn about Reducing Pesticide Use & Impacts

 

Authors
Scott Black is an internationally renowned conservationist who has been at the forefront of the conservation movement for three decades. Scott’s work has led to protection and restoration of habitat on millions of acres of rangelands, forests, and farmland as well as protection for many endangered species. He is an author of the best-selling Attracting Native Pollinators and Gardening for Butterflies and has written more than two hundred other publications including a recent chapter on climate change and insects.

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