By Leslie Mertz
Anyone who has tended a lawn is probably very familiar with white grubs. They are the fat, cream-colored, brown-headed larvae that can grow up to an inch long, and are usually discovered in the soil lying on their sides rather inertly and curled into a C-shape. Several species of scarab beetles have larvae that look like this, but members of the native genus Cyclocephala are particular pests of turfgrass, and they are commonly known as masked chafers.
Gardeners, golf-course owners, and growers who have been battling masked chafers for decades now have a new resource. An article in the Journal of Integrated Pest Management (JIPM) delves into five of these turfgrass pests and the options for managing them. The five species include the northern masked chafer (C. borealis), which is common in the northeastern quarter of the United States; the southern masked chafer (C. lurida), found mainly in the southeastern quarter of the country; and three other species that are known only by their scientific names: C. pasadenae and C. hirta, which are distributed through much of the southwestern United States, and C. parallela, which lives in parts of Florida.
“I became interested in these insects because they are among the hardest grub species to control,” said Sudan Gyawaly, lead author of the article. He is a doctoral student in the Department of Entomology at Virginia Tech University.
According to Gyawaly, damage from the masked chafer comes from only one life stage.
“The adults of many scarab beetles feed on plants, but adult masked chafers do not. It is the larvae that are the major pests,” he said.
Those larvae can become very large and destructive populations in some regions of the country, particularly in southern stretches of the Midwest where the ranges of northern masked chafers and southern masked chafers overlap.
Masked chafer larvae cause their damage by eating the roots of turfgrass. During rainy periods, the grass plants may still be able to send up healthy-looking, green blades, so lawns appear to be doing well. When drier conditions prevail, however, the gnawed-away root system causes the grass to turn brown and die.
“Because the grubs have fed on the roots, you can pull up the turfgrass (from the soil) like a carpet,” Gyawaly said.
High concentrations of white grubs can also draw in insectivores, such as skunks and raccoons, which can cause considerable injury to turfgrass as they excavate the ground in search of the tasty larvae, he noted.
Control measures for masked chafers typically include chemical insecticides. While they do work, chemicals have in some cases been shown to harm bees and other beneficial insects. For that reason, many researchers, including Gyawaly, are investigating additional grub-fighting tactics that may reduce the need for the chemicals.
Gyawaly is especially interested in biological approaches to reduce grub numbers. This includes the use of entomopathogens, which are organisms that cause disease in insects. He is taking a closer look at the effects of entomopathogenic fungi when paired with chemical insecticides.
“We are getting pretty good results with this approach in the lab, but we aren’t getting the results I was expecting in field experiments,” he said. “We need to develop some other techniques to increase the efficacy of using entomopathogenic fungi in the field in combination with insecticide.”
While that work is progressing, he said he hopes this new JIPM paper will provide a good overview of all of the masked chafer species that are major U.S. turfgrass pests.
“We have a good understanding of the biology of the northern and southern masked chafers, and we have book chapters and publications that talk about these two species. But we don’t know the biology of C. pasadenae, C. hirta, and C. parallela very well, so they often go ignored,” he said. “That’s why I wanted to write this inclusive paper that mentions all of the important species we have in the United States and updates the management information to show how far we have come in terms of their control.”
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Leslie Mertz, PhD, teaches summer field-biology courses, writes about science, and runs an educational insect-identification website, www.knowyourinsects.org. She resides in northern Michigan.