Though barely more than a millimeter in length, the tiny wasp Ooencyrtus nezarae (right) can take a big bite out the invasive kudzu bug (Megacopta cribraria, left). The wasp species, native to Asia, was discovered parasitizing kudzu bug egg masses in North America for the first time in the summer of 2016 and shows promise as a potential biological control for kudzu bug, a pest of soybean and other legume crops in the southern United States. (Images originally published in Ademokoya et al 2018, Journal of Insect Science)

When the kudzu bug (Megacopta cribraria) showed up in the southern United States in 2009, it at first appeared to be the beginning of another frustrating story of an invasive insect running wild in a new environment. While M. cribraria, native to Asia, feeds on kudzu (an invasive plant itself), the insect also feeds on soybean and other legume crops, and it has become a significant pest for growers particularly in Georgia and South Carolina.

But then a small Asian wasp came to the rescue: Paratelenomus saccharalis, a parasitoid that lays its eggs in kudzu bug eggs, was discovered in Georgia in 2013, likely having arrived accidentally via trade, just as the kudzu bug did. And now P. saccharalis has a new partner in parasitism, according to entomologists at Auburn University and the U.S. Department of Agriculture (USDA).

In a paper published Tuesday in the open-access Journal of Insect Science, researchers describe the discovery and identification of the wasp Ooencyrtus nezarae parasitizing kudzu bug eggs in Alabama. Previously known to inhabit several countries in Asia as well as Brazil (where it was introduced as a biological control agent for stink bugs), O. nezarae offers promise as another useful biological control agent against kudzu bug in the U.S. In the kudzu bug egg masses collected in the study, an average of 95.6 percent of the eggs were parasitized by O. nezarae.

Kudzu bug populations in the southeast United States have declined after peaking between 2010 and 2013, but knowledge of additional natural enemies of the pest can only help, says the lead author of the study, Blessing­ Ademokoya, a graduate researcher in the lab of Henry Fadamiro, Ph.D., at Auburn at the time of the study and now a Ph.D. student at the University of Nebraska-Lincoln. The research project was supported by USDA National Institute of Food and Agriculture and the Alabama Agricultural Experiment Station.

“It is exciting to know that many natural enemies are in the field helping to keep kudzu bug populations under control,” Ademokoya says. “And, with this latest addition, we have a potential explanation for the decline observed in kudzu bug densities across several locations in the southeastern U.S.”

Parasitoid wasps Ooencyrtus nezarae and Paratelenomus saccharalis both lay their eggs in the eggs of other insects, including those of the invasive kudzu bug (Megacopta cribraria). O. nezarae, discovered in North America for the first time in 2016 and reported this week in the Journal of Insect Science, emerges from a hole on the side of kudzu bug eggs (shown at left) whereas P. saccharalis emerges from a hole at the top of the egg (right). (Image originally published in Ademokoya et al 2018, Journal of Insect Science)

Co-author Rammohan Balusu, Ph.D., notes that, in Asia, O. nezarae is a parasitoid of several insects in families including Pentatomidae, Coreidae, Alydidae, and Plataspidae. “Ooencyrtus nezarae is a generalist known to parasitize eggs of several species of true bugs. As such, we believe it could serve as a biocontrol agent of other heteropteran pests,” Balusu says. “Its presence in the U.S. means we have an additional natural enemy of agricultural pests.”

Despite O. nezarae‘s high parasitism rate of kudzu bug, like P. saccharalis it has a short period of activity. Fadamiro says continued research will be necessary to identify tactics for use of the parasitoid in kudzu bug management.

“Monitoring needs to be carried out to know the distribution of the parasitoid in the U.S. and to determine its seasonal phenology in the field. This is very important to maximizing its effectiveness,” he says. “We are also interested in studying the nutritional ecology of this parasitoid and strategies for its conservation in the field.”