Yellow sticky traps for monitoring levels of Asian citrus psyllid (Diaphorina citri) illustrate the reduction in bycatch when using tulle mesh as a screen. Researchers led by Texas A&M’s Mamadou Sétamou, Ph.D., say the mesh-covered traps reduce bycatch almost to zero while maintaining effectiveness in capturing psyllids. (Image originally published in Sétamou et al 2019, Journal of Economic Entomology)

By Meredith Swett Walker

Meredith Swett Walker

If you’ve ever visited an orchard, you’ve likely seen sticky traps: adhesive-coated cards with some sort of alluring odor or color. These simple devices are used widely by pest managers to monitor for flying insect pests. For instance, yellow or lime-green sticky traps are used to monitor citrus groves for the Asian citrus psyllid (Diaphorina citri). These tiny, sap-sucking insects carry the bacteria that cause citrus greening disease (also known as Huanglongbing), which can devastate a grove. But sometimes the sticky traps work a little too well.

“What we’ve noticed is not only we will catch the psyllid, we also had some bycatches,” says Mamadou Sétamou, Ph.D., professor of citrus entomology at the Texas A&M University Kingsville Citrus Center. “In some instances, we were catching lady beetles or lacewings,” he says. “Even lizards and birds.” Many of these unintended victims of the sticky trap are actually beneficial organisms that help control pests. Because sticky traps are widely used in many agricultural settings and deployed in large numbers, they could be doing a significant amount of accidental damage. In addition, the build-up of non-target insects and debris on the cards makes it harder for pest managers to actually detect the target pests.

Asian citrus psyllids (Diaphorina citri) can transmit the bacteria that cause citrus greening disease, which can devastate citrus groves. (Photo credit: Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org)

Inexpensive and widely available tulle fabric can reduce the amount of non-target organisms and debris stuck to sticky traps.

But Sétamou may have found a simple, inexpensive solution to this sticky problem. In a report published in March in the Journal of Economic Entomology, Sétamou and colleagues from the University of Texas and Alpha Scents, Inc., describe an ingenious way to modify sticky traps to reduce bycatch. The researchers applied a layer of nylon tulle mesh—the kind sold in fabric stores to make bridal veils and ballerina tutus—over the surface of the cards. The mesh acted like a sieve, preventing larger, non-target organisms from getting stuck in the adhesive while still allowing the tiny psyllids to pass through and get stuck.

Mamadou Sétamou, Ph.D., is professor of citrus entomology at the Texas A&M University Kingsville Citrus Center. He says sticky traps for monitoring for the Asian citrus psyllid (Diaphorina citri) in orchards often catch other insects such as lady beetles or lacewings, and even lizards and birds. Looking to reduce such bycatch, Sétamou and colleagues turned to a simple solution: tulle mesh fabric, which acts like a sieve, allowing psyllids to pass through to the sticky trap but keeping larger nontarget organisms out. (Photo courtesy of Mamadou Sétamou)

Tulle comes in a variety of hole sizes, colors, and styles. Because psyllids are attracted to sticky traps by a visual cue (color), the addition of tulle could reduce the trap’s attractiveness. So, the researchers tested three styles of tulle to determine which caught the most psyllids. White and yellow tulle-covered traps caught significantly fewer psyllids, but the addition of gold, glittery tulle did not reduce the number of psyllids trapped.

Why would these tiny insects have a penchant for razzle-dazzle styles? “Psyllids love light,” says Sétamou. He suspects that the white mesh, for instance, may have altered the reflectance of the trap and made it less attractive, whereas the glittery gold mesh blended in with the color of the trap and made it shinier. It “works like a charm,” says Sétamou.

The glittery gold tulle layer did not make sticky traps any less effective at detecting psyllids. Sétamou and colleagues simultaneously deployed tulle-covered and uncovered traps in citrus groves and recorded the numbers of psyllids, as well as the amount of bycatch and debris, stuck to the cards. Statistical analysis revealed that the tulle covering did not reduce the ability of the traps to detect psyllids, and the number of psyllids caught on covered traps was significantly correlated with the numbers caught on uncovered traps.

But, importantly, the tulle significantly reduced the amount of bycatch and debris stuck to the cards. The number of flies stuck to the tulle-covered cards was reduced by 95 percent, while capture of other non-target organisms and debris was reduced to zero. Not only does this protect beneficial organisms like lady beetles and lacewings, but it also makes sticky traps more pleasant for pest managers to use. Sétamou notes that when large amounts of bycatch (like flies) sit on a card for a few weeks they begin to decay. “Those traps may be unusable,” says Sétamou. “The whole thing stinks so much, you don’t want to touch it.”

Adding a layer of inexpensive tulle to sticky traps makes them safer for non-target organisms and easier for pest managers to use—without reducing their effectiveness. “Sometimes a particular problem doesn’t need a complicated solution,” Sétamou says. “It’s simple solution”—albeit a sparkly one.

Meredith Swett Walker is a former avian endocrinologist and wannabe entomologist. She now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. Find a sampling of her work at www.magpiescicomm.com.