Kudzu bugs may have met their match in one Clemson University graduate student.
The kudzu bug is an invasive soybean pest first discovered in Georgia in 2009. It has since spread to 13 states and Washington, D.C. Research by Francesca Stubbins, an entomology graduate research assistant at the Edisto Research and Education Center (REC), shows for the first time that mermithid nematodes can infect and kill the insects. Stubbins’ research involved collecting kudzu bugs from soybean fields. Nematodes — long, slender, parasitic worms — were found in the abdomens of some of the dissected female insects.
“My overall research is based on the ecology of the kudzu bug and implications for management,” Stubbins said. “While doing dissections for a project to describe the population dynamics and the population structure of the kudzu bug through assessment of reproductive status, I found nematodes inside females.”
Stubbins also found nematodes inside kudzu bug males and nymphs.
“Not much work has been done on the Mermithidae family of nematodes so we do not know much about them,” Stubbins said. “We do know they live in soil for long periods of time and that they have been shown to infect different insect species.”
The nemotodes enter insects as immature nematodes, develop while inside the insects, emerge into the soil, develop and become adults, then lay eggs. Hatched immature nematodes find insects to infect and the cycle continues.
“This discovery adds to the list of natural enemies that infect kudzu bugs,” Stubbins said. “We don’t know if this nematode has a significant effect in reducing kudzu bug populations as it has just been found in kudzu bugs in one field at the Edisto REC, but it does show there are natural enemies in the field that could have the capacity to reduce kudzu bug populations. This is good news for soybean growers.”
The economic importance of this find to both urban and rural environments could be significant, which means more research is needed.
“Insecticides are the most commonly used method for managing insects such as the kudzu bug,” Stubbins said. “But insects can become resistant to insecticides. The continuous threat of insecticide resistance emphasizes the need to investigate other alternatives. We believe our findings provide a basis for justified future research to examine the impact of mermithid nematodes for use as a biological control option for kudzu bugs.”
This research is funded by grants from the USDA and the South Carolina Soybean Board.
The researchers also are studying other possible biological control options for kudzu bugs. One of these options is the fungus Beauveria bassiana, which was found in many South Carolina soybean fields in 2015.
“We think this fungus has a significant effect at reducing kudzu bug populations as insects have been seen covered with the fungus out in the field,” Stubbins said. “Work will be undertaken this summer at the Edisto REC to research the effects this fungus has on kudzu bug populations.”
Soybeans are an important crop in South Carolina. According to the USDA National Agricultural Statistics Service, 465,000 acres of soybeans are estimated to have been harvested in South Carolina in 2015, up from 440,000 acres harvested in 2014.
Photo: Once a nematode has developed, it leaves the insect and emerges into the soil where it becomes an adult and lays eggs.
Image Credit: Francesca Stubbins/Clemson University