How insect interactions vary with height in turf

Like the different environments of a forest floor and treetops, insect interactions vary in the smaller scale vertical areas of a turf “canopy”. Researchers using clay models of caterpillars to attract predatory arthropods reveal the difference a few centimeters can make. Here is a schematic diagram of the experimental setup used in a new study by entomologists at the University of Georgia, in which clay models were placed at different heights in a turf environment. (Image originally published in Khan and Joseph 2022, Journal of Insect Science)

By Ed Ricciuti

Ed Ricciuti

Ed Ricciuti

Scientists who tricked arthropod predators of turf pests by chewing on fake clay caterpillars have revealed how the life-and-death struggles hidden in greenery could yield a huge benefit to natural lawn pest control, golf courses and sod farms. Experiments using the counterfeits in Bermuda grass (Cynodon cocksfoot), an essential warm-season grass, show that predators are most active near the ground, according to a paper published this month in the open-access journal Journal of Insect Science.

Like a forest – but, of course, much shorter – the turf is stratified vertically into vegetative zones, the lowest of which is made up of soil and thatch, while the middle and upper zones are made up of stems and leaves. Knowing the levels at which predators forage and forage is critical to natural pest control planning, say Fawad ZA Khan, Ph.D., and Shimat V. Joseph, Ph.D., of the Department of Entomology of the of Georgia.

Shimat Joseph, Ph.D.

Shimat Joseph, Ph.D.

Fawad Khan

Fawad Khan

“We observed predator activity at all levels, but predator interactions were more abundant at the lower level than the others, for the most part,” Joseph explains.

When natural pest control is an option, predators can be recruited in the first wave of pest attacks, with chemical follow-up if necessary. “The behavior of arthropod predators, especially foraging and feeding behavior in turf areas, determines the fate of natural pest control,” the researchers explain.

The catch, they say, is that it has been very difficult to determine exactly where in the turf strata the predators are most active. Unlike kills of large predators, prey remains in the grass mini-world are few and far between. Ants, for example, crawl through all levels of grass and encounter prey species as they prowl, but they leave little or no evidence of their predation. To remedy the lack, Khan and Joseph glued clay models onto cardboard attached to stakes, driven into the ground and positioned in each of the vertical areas of grass. The jaws and claws of predators leave scratches, cuts and other signature imprints on the models which can then be examined.

In the new study, these telltale signs were most prevalent — and most pronounced — on models placed on or near the surface of thatch, the researchers say.

This modeling technique, used with vertebrates, was adapted for use with arthropods by Kahn and Joseph. The green clay models are crude caterpillar emulations, lacking detail. As a typical fishing lure proves, an exact replica is not necessary to trigger predatory behavior; only the proper form or function will do. The caterpillars of the noctuidae, which include major turf pests such as the fall armyworm (Spodoptera frugiperda) and black cutworm (Agrotis ipsilon), were the model model. Their two caterpillars move around the stem, leaves and grass thatch.

Turf is one of the largest agricultural crops in the country. The USDA’s National Survey of Agricultural Statistics puts the value of the US turfgrass industry at over $1.1 billion. Turf management is a $40 billion industry, covering approximately 50 million acres of sports fields, golf courses and other green carpets.

Lawn management involves keeping it at a specific mowing height, which varies depending on factors such as aesthetic needs, climate zone, use and type of grass. Mowing height can be critical for pest control. Research shows that predatory rove beetles (Coleoptera: Staphylinidae) and spiders (Araneae) increase with the mowing height of cool season grass. Greater beetle predation Ataenius spretulus larvae, which damage roots, have been reported on annual bluegrass golf courses (Annual poa) maintained at 5 centimeters in height than on fairways maintained at 1.5 cm. The authors point out, however, that “the vertical distribution of predator activity patterns in the warm-season turf canopy is still unclear,” a gap their research attempts to address. They note that “the experiments were conducted on Bermuda grass, and it is uncertain whether predator behavior varies by turfgrass genotype and their growth pattern, leaf texture, and management practices” . However, it is known that the presence and abundance of beneficial arthropods can vary between types of grass.

The authors say their findings “can be used to refine management strategies, such as mowing height and use of insecticides, to effectively manage arthropod pests and beneficial arthropods that feed on soil and leaves.” . The deployment of insecticides, for example, should aim to avoid reducing populations of beneficial predators. The researchers urge more research into factors such as mowing height and cultural practices that could influence predation rates in various types of turf.

“Clay models could be further used to understand the ecology of arthropod predators, such as their distribution in turf landscapes, the off-target effects of pesticides on turf, and to develop strategies to enhance their activity” , says Joseph.

Ed Ricciuti is a journalist, author and naturalist who has been writing for over half a century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His missions have taken him around the world. He specializes in nature, science, conservation issues and law enforcement. A former curator at the New York Zoological Society, and now the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.