Larvae of lacewings in the genus Chrysoperla are natural predators of aphids, mites, and other soft-bodied plant-eaters and thus can serve as useful biological control agents in agricultural settings. (Shown here is an unidentified Chrysoperla adult.) New research has found that a species previously known to Africa and Asia, Chrysoperla zastrowi, has naturalized in the Americas. Its apparent establishment in arid regions of the southwestern United States, Mexico, and Guatemala suggests it is climatically suited to the area and could be a prime candidate for biocontrol applications, researchers say. (Photo by Whitney Cranshaw, Colorado State University, Bugwood.org)

By Paige Embry

Paige Embry

Aphids, mites, and other soft-bodied plant-eaters can be the bane of farmers. Green lacewing larvae in the genus Chrysoperla are fierce predators of these small plant-eaters, and insectaries around the world raise them for use as biological control agents.

Many of these commercially raised lacewings are part of the Chrysoperla carnea-group, which has historically been considered to be one holarctic species. “For years it was considered that there was one species of the so-called carnea-group,” says Charles Henry, Ph.D., emeritus professor at the University of Connecticut. “It was found all over the world. It was traded between countries as a biocontrol agent.”

Charles Henry, Ph.D.

However, research in recent decades has found that the group actually contains 20-plus species—the problem is telling them apart because, morphologically, there is little to distinguish them. In a new study published in January in the Annals of the Entomological Society, Henry and a team of colleagues at the University of Connecticut; the Swiss Federal Institute for Forest, Snow and Landscape Research; and Mexico’s National Center for Biological Control Reference showed that, in the last 10 to 15 years, an old world species of the C. carnea-group, Chrysoperla zastrowi, has naturalized in the Americas.

It’s been found both in insectaries and the wild, in arid areas ranging from Guatemala to the southwestern United States. Since C. zastrowi is ideally suited to hot, arid regions, the authors suggest that this naturalization could be a boon to farmers in those areas, allowing them to use this well-suited species for biocontrol.

Being able to identify this new species was possible due to decades of research, and it focuses on the songs that the lacewings sing. (Nowadays, identification is aided by certain morphological features and DNA.) Many insects “sing,” and it’s usually the males that announce their presence to potential mates in this manner. Some sing loudly enough that we can hear them, like with cicadas or grasshoppers. Members of the C. carnea-group, however, sing quieter songs—vibrating their abdomens above a leaf or twig, which sends reverberations along that substrate.

Lacewings “sing” songs by vibrating their abdomens above a leaf or twig, which sends reverberations along that substrate. Either the male or female will start and the other will join in—called “duetting.” If they are singing the same tune, they’ll copulate. And every species has its own tune. (For more examples, see “The Cryptic Song Species of Chrysoperla,” a web page hosted by Charles Henry, Ph.D., emeritus professor at the University of Connecticut.) Shown here are oscillographs (lower of each pair of traces) and sonographs (upper traces) of a solo vibrational song recorded from (a) a specimen of the Chrysoperla carnea-group collected in Bangalore, India; (b) a specimen of the C. carnea-group collected in Blythe, California; and (c) a specimen of the C. carnea-group collected near Guatemala City, Guatemala. (Image originally published in Mandese et al 2021, Annals of the Entomological Society of America)

Humans need special equipment to hear Chrysoperla lacewings’ songs. Not only do they sing quietly, but both sexes sing. Either the male or female will start and the other will join in—called “duetting.” If they are singing the same tune, they’ll copulate. And each Chrysoperla species has its own tune.

The difficulty of identifying the species means that commercial insectaries have been selling, and sometimes continue to sell, insects labeled as one species, Chrysoperla carnea, that aren’t. Despite this, Henry says, “We have almost no examples of forms that were introduced from one continent to another by an insectary where they’ve become established. There were thousands and thousands of one species of lacewings that were introduced to New Zealand as a biological control agent back in the 1930s or 20s, and not a one of them has survived beyond one year.”

Yet in 2010 a group of scientists found the Afro-Eurasian species, Chrysoperla zastrowi sillemi, in a hot dry corner of California—a habitat for which it is extremely well-suited. “We’ve been collecting up and down the coast for years,” Henry says, “and I’ve collected in this area—certainly 15, 20 years ago—and never found any traces. They’ve clearly come recently.” Within the next several years, people found C. zastrowi in Mexico and Guatemala as well.

The authors of the Annals paper state that C. zastrowi has naturalized in parts of North and Central America. They write, “Although climatic upheaval and associated species’ range extensions and retractions are often viewed with alarm, we need to be cognizant of a silver lining in this case.” They suggest that C. zastrowi should be widely used in the hot, arid areas where it already exists, whether it is native or naturalized.

The authors suggest developing a simple method for identifying C. zastrowi—perhaps via a search for mitochondrial DNA haplotypes that isolate them from their relatives or an app to recognize their song. A simple identification method would allow insectaries to send C. zastrowi, rather than other random, possibly climatically ill-suited Chrysoperla species, to areas where they will be the most beneficial.

“We should seize the opportunity,” the authors write, “to consider ways in which those natural adaptations of C. zastrowi to hot, dry habitats might be utilized to increase the efficacy of existing programs of lacewing-based pest control in new agricultural settings.”

Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.