Work On Burrower Bug Continues

The peanut burrower bug is a tricky pest. Not only is an infestation invisible in a field from above the ground, damage done by the bugs’ piercing mouthparts can only be detected after peanuts are harvested and sent for processing, resulting in revenue loss.

University of Georgia entomologists, along with Extension agents, continue to monitor peanut producers’ fields for the subterranean bug while looking for methods of control. The only pesticide effective against the peanut burrower bug, chlorpyrifos, was banned in 2021.

Sporadic But Significant Damage

Mark Abney, UGA researcher and Extension peanut entomologist, recounts that peanut burrower bug is native to the United States but had not been specifically recognized as a pest in Georgia until 2010. “It was first reported as a pest in Texas in the 1970s, but we didn’t hear a lot about it in Georgia.” It was in 2010 that burrower bug showed up in a big way in producers’ fields.

Related to stink bugs, peanut burrower bugs are “smaller than a pinky fingernail. In the family Cydnidae, they are true bugs, a specific type of insect with piercing-sucking mouth parts. Their mouths are like a hypodermic needle that pierces through the hull of the peanut to the seed — they suck the juice out of the seed,” Abney says. This results in sunken, yellowish, brown or black lesions on the peanut seed, often multiplied due to repeated feedings.

Economically Devastating

While peanut burrower bug has not caused as much widespread damage in Georgia since 2010, the potential for damage from the bugs is always present and is difficult to predict and control.

“This is a sporadic pest in that the injury is sporadic. The insect is pretty common. For several years we used light traps all over south Georgia, and everywhere we put a light trap, we would catch peanut burrower bug, no matter where we were or whether there was a history of injury or not,” Abney says. “From a research standpoint, the big, glaring question is why was this such a problem in 2010? And now, why will one grower have a problem with peanut burrower bug, but his neighbor does not? One year a farmer’s peanuts are rated segregation 2, and the next year it doesn’t happen. That has been the focus of a lot of research.”

Limited Control Methods

Solutions to control peanut burrower bug are limited. Aside from the now-banned insecticide chlorpyrifos, peanut burrower bug is mainly controlled through deep tillage — a practice not used as much anymore because of the switch to conservation tillage.

“The more aggressive the tillage, the lower the risk is of having burrower bug injury. There are a lot of good environmental and economic reasons to use conservation tillage, but a lot of producers have gone back to more aggressive tillage or discing because it is the only tool our growers have since the one chemical tool we had is no longer available,” Abney says. “We’ve looked at virtually every insecticide that is approved for use in peanut — and some that were not — and even if we find that there are insecticides that have activity against the bug, there is no way to deliver it to the populations in the field as they exist.”

In the field, the bugs spend most of their time underground. Because they don’t feed above ground, it is difficult both to scout for the bugs and to target them with an insecticide. While Abney has worked steadily on the problem since joining UGA, he says it is difficult to perform research on peanut burrower bugs because both finding them in the field and keeping them in lab colonies for testing has been a challenge.

“The population is so sporadic, it is hard to get data on them,” he says.

Looking For Risk Factors

Ben Aigner, a doctoral student on Abney’s team, is currently working to identify risk factors that may contribute to the presence of peanut burrower bugs and burrower bug injury in any given year. His research is funded through grants from the Georgia Peanut Commission, the National Peanut Board and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

“Ben has a record of nearly all burrower bug injury in the state for four years, then he spoke to growers about what they did in the affected field — crop rotations, management practices, irrigation — and what the environmental conditions were in terms of rainfall. A big part of his job is to put all of that data into a model to explain some of the variations on where burrower bugs are,” Abney says.

While he says there have been no real “Eureka” moments, the team continues to add to the knowledge base about the bugs in the continuing effort to find solutions.

“It tends to be worse in non-irrigated fields, but it can occur in irrigated fields. It can be worse in certain types of soil, but it can be in any type of soil. It would be easy to sensationalize the burrower bug, but the truth is that, more often than not, the problem is limited to a relatively small proportion of the total crop in Georgia year over year,” Abney says. “If growers could get peanut burrower bug insurance, no one would care, but that is not an option. It is truly an existential threat for growers in high-risk areas.”

Until then Abney will continue to work on this and all pest problems as the only dedicated peanut entomologist.

“We have been working to identify alternative (pesticides) for five years for burrower bugs and rootworms,” he says. “Solving entomological problems for farmers is what makes me happy. There are a lot of farmers whose livelihoods depend on what I do and that is why I do it.” PG