Termite pellets can linger long after the insects that dropped them have disappeared. By testing for microbes in the excrement, researchers can distinguish old droppings from fresh, and whether a colony is actively chewing its way through a home. 

Previous efforts to determine pellet age focused on testing hydrocarbon compounds or other chemicals in the pellets.  These studies have required expensive, specialized laboratory equipment and complicated extraction processes. 

In some cases, researchers tried analyzing changes in pellet color over time, but found too much variation depending on the termites’ diet to make the approach reliable. 

In contrast, a new UC Riverside study details the first time researchers are using a straightforward and scalable method: examining microbes to learn about the age of the droppings. The study, published in the Journal of Economic Entomology, could give rise to a simple test that could be used for rapid on-site infestation assessments.

Termites host thriving communities in their bodies. Bacteria, protists, and even microbes living inside the protists all contribute to digestion and form entire microscopic communities working in concert to help the insects digest wood.

“These microbes are naturally secreted along with the poop, but many of them are anaerobic, meaning they only do well in oxygen-deprived conditions,” said Dong-Hwan Choe, UCR entomology professor and study senior author. 

“Once they come out of the insect and into the open air, they die quickly, and their DNA begins to degrade,” Choe said. “This microbial DNA sends a fading, but unmistakable signature that we can use to track time.”

Nick Poulos, UCR entomology researcher and first author of the study, collected drywood termites and fed them two types of wood: natural hardwood and Douglas fir. The latter wood was included specifically because it is the most common wood used for house framing, making the study especially relevant for real-world infestations.

The termites generated pellets, which were then sampled when fresh and aged three months, six months, and one year. 

Using a technique called quantitative PCR, Poulos measured a decline in the amount of DNA from E. coli bacteria in the pellets over the course of the year. “The quantity drops nearly 190-fold by the 12-month mark for natural hardwood, and 184-fold for the Douglas fir-derived pellets,” Poulos said. 

This massive drop in the quantity of microbial DNA from the fresh to six-month mark was observed both for the pellet samples obtained from the hardwood as well as the Douglas fir-fed termite colonies. The researchers also looked at whether the types of microbes detectable in the pellets changed over time.

“Not only did the quantity of bacterial DNA drop dramatically, but the composition also changed over time,” Choe said. “The anaerobic bacteria become less abundant and disappear as bacteria that favor aerobic conditions start to thrive.”

Ultimately, the research team would like to collaborate with other scientists and engineers to create sensors that detect bacteria in the pellets. 

“We would like to create a lateral flow assay, like a COVID-19 test. You’d have a strip and some fluid that gives you an indication of whether your home is infested,” Poulos said. 

Armed with knowledge from such a device, pest professionals could ultimately use fewer chemicals. 

“Maybe, if the pellets turn out to be old, we can avoid unnecessary fumigations, and engage in active treatment only when it’s really needed,” Poulos said. 

(Cover image of termite colony: Dong-Hwan Choe/UCR)