Pittcon poster probes a disease vector’s microbiome, and finds pharmaceuticals in its habitat

Black flies, sometimes known as “buffalo gnats,” may not be as widely recognized as the common housefly, but they are undeniably more pernicious. Females of most black fly species need a blood meal to produce eggs, and rather than cleanly piercing the skin like a mosquito, they slice it open and lap up the pooled blood. The process can leave behind saliva that can trigger swelling immune reactions. Certain species also carry parasitic worms linked to river blindness (Onchocerca volvulus) chiefly in sub-Saharan Africa and Yemen, with smaller remaining foci in Latin America, a condition the CDC classifies as a neglected tropical disease that can inflict “tremendous disability.”

Despite all that, they often remain overlooked in the U.S. “Farmers are concerned about them because of the diseases they transmit,” said Sarah Palmeri, a graduate researcher in SwRI’s Pharmaceuticals & Bioengineering Department who recently completed her master’s degree at Texas A&M University–San Antonio in an interview at Pittcon. “But largely, research kind of looks away from them.”

Exploring how urban streams can impact the environment

For her thesis, she set out to study what an urban stream, one fed by wastewater effluent, might be doing to the gut microbiome of black flies living in it. The question grew out of a seminar where she heard a researcher describe how pesticides reshaped the microbiome of frogs. “I wondered, what if we did it with black flies?” she said. “And instead of looking at how one compound is affecting them, we looked at how the natural environment is affecting them.”

Part of what motivated the work was proximity to risk. Joint Base San Antonio–Lackland trains military working dogs, with roughly 800 dogs on site as of 2019, and Palmeri noted those animals could be vulnerable to Onchocerca lupi, an ocular parasite related to O. volvulus that has caused severe eye disease in dogs in the U.S. In 2020, a dog in South Texas with no travel history required enucleation after an O. lupi infection perforated its cornea. Black flies are considered a likely vector for the parasite, though that transmission pathway is still being established.

Because black fly larvae develop in fast-flowing water, Palmeri focused on populations living downstream of a San Antonio wastewater treatment plant. Mapping the full chemical profile of that water required advanced mass spectrometry equipment that led her to SwRI. The institute granted her a research internship, and what she found was a number of chemicals related to human activity: “We found a lot of anthropogenic contamination,” she said. “We found caffeine, vitamins… The more significant one to me is butalbital, because that’s a barbituate.” The researchers also found beta-blocker propranolol, and ritalinic acid, a breakdown product of the ADHD medication Ritalin. Twenty-five percent of the compounds detected had no match in the NIST reference library at all. “It could be something harmless, or it could be something dangerous that we haven’t identified yet,” she said.

A microbiome surprise in the data

Palmeri shared a poster on this work at Pittcon 2026 in San Antonio on Monday, March 9, during the afternoon session (PS-E127): “Characterization of the Gut Microbiome of Blackflies (Diptera: Simuliidae) Across Developmental Stages and Season.” Co-authors include Megan Wise, Texas A&M–San Antonio; Robert Martinez, SwRI; Kristin Favela, SwRI; Taliah Moss, Texas A&M–San Antonio; and Christina Menn, SwRI. The work builds on an earlier survey that established the field sites and identified the primary species as Simulium mediovittatum.

Palmeri’s team found a complete turnover in gut bacteria between larval and adult stages, which was expected given the radical shift from aquatic to terrestrial life. They also found that the adult microbiome changed significantly between seasons while the larval microbiome didn’t budge.

“You would expect, if the adults are changing by season, that the larvae would be changing too, right? But they didn’t,” Palmeri said.

Effluent from the San Antonio Water System plant runs as much as five to ten degrees Celsius warmer than a natural waterway. Larvae developing in that artificially stable environment may never register the temperature shifts that drive seasonal microbial change. “They don’t know what seasons are in this stage,” Palmeri said, “so they didn’t change.”

Within the microbiome data, five bacterial genera stood out: Staphylococcus, Streptococcus, Pseudomonas, Klebsiella and Rickettsiella: genera also reported in other disease-vector microbiomes and potentially relevant to pathogen transmission or population control, though their functional role in black flies is not yet established.. In adult flies, Proteobacteria dominated, accounting for roughly 70% of the gut microbiome. Larval guts were more diverse, with Firmicutes, Chloroflexi, Actinobacteria, and Proteobacteria sharing the balance more evenly.

The pharmaceutical contamination and the microbial findings are linked. Research in fish and other invertebrates has shown that waterborne chemicals can reshape gut flora, and Palmeri said the compounds her team detected were present at frequencies high enough to matter. “All of those at high enough amounts can cause alterations to the microbiome, which can ultimately affect disease transmission,” she said.

An R&D 100 Award-winning tool, evolved

Processing the sheer volume of data required more than commercial software. Palmeri’s team used Highlight, an AI-driven analysis suite developed in-house at SwRI that builds on the institute’s Floodlight software, an R&D 100 Award winner in 2021. The tool uses an iterative method to identify mass spectrometry peaks that conventional software would miss. “It really addresses the chokehold of all this data,” Palmeri said. “Mass spec has become so broad nowadays. There’s so much data available. It’s really hard to sort through it all.”