Biologist Dr. David Lightfoot Weighs in on Grasshoppers

Editor’s Note: This interview originally appeared in New Mexico Wild’s Fall/Winter 2023 Newsletter. With news that the Animal and Plant Health Inspection Service is once again proposing to conduct widespread aerial insecticide spraying near the Rio Chama Wild and Scenic River in 2024, our conversation with Dr. Lightfoot is more relevant than ever. Stay tuned for more on this continuing threat to critical habitats and water quality near the Rio Chama, including how you can engage to help us stop this deeply flawed project.

Can you talk a little bit about your work as a PhD biologist at UNM?
I’m a grasshopper ecologist and a grasshopper taxonomist. I just last summer finished 30 consecutive years of monitoring grasshopper communities in New Mexico. I’m also a taxonomist. I just received my DNA sequencing on a big study that I’m doing on North American grasshoppers to understand their evolution and their taxonomy.

The recent proposal from USDA to spray pesticides in Rio Arriba County was intended to decimate grasshopper populations that compete with cattle for forage. Are there better and safer ways to manage rangelands than this approach?
Livestock overgrazing is promoting population outbreaks of grasshoppers. APHIS [Animal and Plant Health Inspection Service] puts out grasshopper density maps every year. I think they’re fairly accurate in showing where the high densities of grasshoppers are. I would like to overlay a GIS layer of rangeland condition onto a layer of APHIS grasshopper density maps. I bet that there’s going be a very high correlation of the worst range condition has the most grasshoppers. That’s what I’ve seen, over and over again on public rangelands across the West.

How does over-grazing promote grasshopper blooms?
Most grasshoppers prefer dry sunny environments. Their eggs are laid in the soil in little egg pods, and the soil needs to be somewhat dry. It can’t be saturated with water, and it needs to get warm from the sun in order for the eggs to develop and hatch. So most temperate grasshoppers actually do better in situations where there is bare soil exposed to the sun, and it’s not saturated, and the vegetation is not too dense. Livestock overgrazing is actually creating an environment for ecological generalist grasshoppers to do even better than if it wasn’t grazed. So in other words, the livestock overgrazing is promoting populations outbreaks of ecological generalist grasshoppers.

It sounds like overgrazing is really the biggest threat to rangeland health. Do you think that grasshoppers are really a threat to rangelands?
No, I don’t. I think that grasshoppers are an important part of rangeland ecosystems. Grasshoppers are a real important food source for birds and other animals. The view that native grasshoppers are like non-native invasive species that we have to kill is just wrong. They are in fact native species, they’re part of our natural ecosystems and part of natural rangeland food webs. They’re ecologically important, even the herbivory by grasshoppers has an important function for plants, for compensatory growth of the plants and increasing nutrient cycling, which improves rangeland health.

Do we have any invasive grasshopper species in New Mexico that are problematic?
No, not at all. All rangeland grasshoppers of New Mexico are native species.

What are your thoughts on APHIS’s plan to spray carbaryl near the Rio Chama watershed earlier this summer?
To me, it is a huge waste of taxpayer money to benefit a very few people. And it is highly destructive to our native animal communities. Those poisons don’t just kill insects. Carbaryl targets the nerve synapses, and it blocks an enzyme (acetylcholinesterase) that stops the nerve from firing. So the nerve synapses just keep firing. When an animal is hit with this, including vertebrates, they go into convulsions and twitching. It’s a nerve toxin. The animal just basically convulses to death, it’s horrible. [Carbaryl] does impact vertebrates, but they can chemically neutralize the toxin faster than invertebrates. The APHIS-produced Environmental Assessment for the proposed spray project stated that for the pesticide to be used “we conclude that this spray will have no significant adverse effect on any animals or other insects.” That statement was simply a lie.