Mosquitoes may have surprisingly overcome one of humanity’s best defenses against them, coming to associate the smell of DEET with a nearby meal, an international team of researchers says.

In a recent paper published in the Journal of Experimental Biology, the researchers identified that repeated exposure reduced DEET’s repellent effect on mosquitoes. However, their findings don’t end there; the team also discovered that under certain conditions, DEET may actually begin to attract mosquitoes rather than repel them, offering a strange glimpse into nature’s adaptive qualities.

DEET and Mosquitoes

DEET, the common name for diethyltoluamide, is a clear or slightly yellow liquid used to ward off insects, such as ticks, fleas, and mosquitoes. It has been used by the US military since 1949 and by civilians since 1957.

Claudio Lazzari of France’s University of Tours and Clément Vinauger of Virginia Tech led the international study, rooted in Ivan Pavlov’s famous 1890 study of conditioning, in which he noted that any indication that a dog was about to be fed, such as the ringing of a bell, would cause it to salivate, even without the sight of food. 

Yellow fever mosquitoes (Aedes aegypti) were the subjects of the team’s research. This particular species is known to infect millions of humans with deadly diseases such as dengue fever, Zika, yellow fever, and chikungunya every year. 

Feeding Them Blood

Since the insects feed on blood, the team first tested their attraction by placing a bag of warm blood on the other side of a fabric mesh restraining the mosquitoes, to observe how much effort the creatures would expend attempting to stab through to the meal. They found that insects were extremely enthusiastic, yet backed off when the smell of DEET was introduced.

They next devised an experiment to see if that could produce Pavlovian conditioning in the mosquitoes, getting them to associate the smell of DEET with feeding time. In a remarkably short time, the researchers observed a positive result. They began the experiment with 30-second feeding periods, during which the last 10 seconds introduced DEET. After a mere four repetitions of this tactic, the team found that 60% of the mosquitoes attempted to feed solely in response to the smell of DEET. 

Lending further confirmation to the finding, the team offered one of their colleagues, Ayelén Nally, from the University of Buenos Aires, Argentina, a free meal to the insects. One of Nally’s hands was sprayed with DEET, while the other was clean. Surprisingly, the mosquitoes showed a strong preference for the DEET-covered hand over the clean one, once they had been conditioned to associate the scent with food.

DEET Remains Useful

The team repeated the process, next training the mosquitoes to associate DEET with receiving a sugary treat, producing the same effect. The team says their findings indicate that, in the right scenario, DEET may shift from a repellent to an attractant for pests. 

“If a mosquito bites someone who applied DEET to their skin several hours earlier and the concentration of the repellent is too low to repel the mosquito,” Lazzari said, “but still strong enough for the insect to smell it, the mosquito may be more likely to bite people who smell of DEET.”

The researchers say that their work is only the beginning of efforts to better understand how insect repellents work, demonstrating that learned behavior may play a role. Despite their findings, they note that DEET generally works and saves lives by reducing insect-borne illnesses.

“If someone applies DEET and the concentration fades over time, but a mosquito still manages to feed, the insect may begin associating that smell with a reward,” Vinauger concluded. “That’s a possibility we should take seriously when we think about how repellents are used in the real world.”

The paper, “Associative Learning Switches DEET Valence from Aversive to Appetitive in Aedes Aegypti,” appeared in The Journal of Experimental Biology on May 28, 2026.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.

While most fruit flies are known for their attraction to fermenting fruit, one species has evolved to hunt in fast-moving streams in Africa, taking on the role of a predator.

A team of researchers from Lund University has mapped the genome of Drosophila enhydrobia, a fruit fly with a unique life cycle. Its larvae develop underwater in fast-flowing streams, where they prey on black fly and midge larvae. The study, published in Current Biology, reveals how a lineage that was once considered a household nuisance transitioned into a new ecological world and identifies the genetic changes that supported this shift.

“We’re talking about a fruit fly that has completely turned its lifestyle upside down,” said Marcus Stensmyr, biology researcher at Lund University and lead author of the study. “From feeding on yeast and rotting fruit, it has become a specialized predator in running water.”

Museomics Provides an Answer

D. enhydrobia has not been observed in the wild since 1981. To obtain genetic material, the research team located a single pinned specimen in a natural history museum in Zurich and used modern DNA techniques to extract an almost complete genome without damaging the specimen.

This method, called museomics, is part of a wider effort to recover genetic information from museum collections that wasn’t accessible when the specimens were first collected. The Zurich specimen, preserved for about 40 years, still contained enough intact DNA for the researchers to conduct both phylogenetic and comparative genomic studies. Earlier technology could not have achieved this result.

Not an Evolutionary Loner

One of the main findings is that D. enhydrobia is not as biologically isolated as once believed. Genomic analysis shows it belongs to a group of flies linked to water-adjacent habitats, mostly in South Asia. Its relatives already possess traits that have evolved into an extreme aquatic lifestyle in this species.

“What at first looked like an evolutionary mystery turned out to be an extreme elaboration of something that already existed,” Stensmyr said. “That makes the story both more understandable and, in a way, even more fascinating.”

A Genome Trimmed for a Different Life

Genomic analysis reveals evidence of genetic trade-offs associated with adaptation to an aquatic environment. The analysis shows that the species has lost several gene families involved in smell, taste, and metabolism, which fruit flies that feed on fermenting food typically rely on. For a species whose relatives rely on chemosensory detection to find food and mates, these losses are significant. The remaining sensory genes display signs of intensified selection, suggesting adaptation to new ecological pressures.

“It’s as if it has fewer tools in the toolbox, but the tools that remain are all the more finely tuned for this particular environment,” said Hamid Ghanavi, a biology researcher at Lund University and co-author of the study.

The findings suggest that major evolutionary shifts can involve losing functions that no longer serve a species, while refining those that do.

The Potential of Museum Collections

In addition to its evolutionary findings, the study is a prime example of the value of natural history collections worldwide. Specimens collected many years ago can now provide new genetic insights thanks to modern sequencing technology.

For species that have disappeared from the wild or gone unobserved for years, museum archives may offer the only source of available biological material. The D. enhydrobia specimen examined in this study serves as an example of this; without it, the genetic history of this unusual fruit fly would have remained unknown.

Stensmyr said his team has only scratched the surface of what those collections might contain. Continued advances in ancient DNA recovery could make museum archives a significant resource for tracking how species have evolved over time and how they might respond to future environmental shifts.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.

In the vast and intricate landscape of the mammalian genome, the Y chromosome often attracts attention for its unique characteristics and evolutionary quirks. Although it stands as the smallest chromosome in mammals and is diminutively shrinking over time, the Y chromosome wields substantial influence, chiefly through its indispensable role in male fertility. Recent groundbreaking research emerging from the University of Michigan Medical School sheds new light on how the Y chromosome defends its genomic territory against decay and gene loss by harnessing innovative genetic mechanisms. This study, published in the prestigious journal Current Biology, focuses on deer mice as a model organism to elucidate these molecular ballet moves that preserve the vigor of the Y chromosome.

Chromosomes are typically divided into sex chromosomes and autosomes, the latter encompassing all chromosomes that do not determine sex. Traditionally, the Y chromosome has been perceived as a genetic wasteland where genes inevitably wither due to its lack of recombination—the genetic reshuffling process that maintains gene integrity in other chromosomes. This absence of recombination forces the Y chromosome into a precarious evolutionary path, often described metaphorically as a “graveyard” for genes. However, the University of Michigan study disrupts this narrative by uncovering a vibrant genetic saga unfolding on the Y chromosome, marked by a complex gene family expansion that bucks the conventional decline.

Ivan Mier, an M.D./Ph.D. candidate and former lab manager in Jacob Mueller’s lab, draws an arresting comparison: “You can think of the X and Y chromosomes as rival political parties in a relentless genetic tussle.” Interestingly, they discovered that one gene from the X chromosome, initially migrating to an autosome, later made a surprising leap to the Y chromosome—essentially switching allegiances in this chromosomal rivalry. This unprecedented finding challenges longstanding assumptions about the immutability of sex chromosome gene content and suggests a dynamic evolutionary interplay governed by gene mobility and strategic genomic positioning.

Central to this discovery is a novel gene family named Phf8y, which reveals an extraordinary genomic translocation and amplification process. Unlike typical gene decay observed on the Y chromosome, Phf8y has not only relocated from the X chromosome to an autosome but subsequently “jumped” to the Y chromosome, duplicating itself there. This phenomenon, according to Mier, is “a unique pattern that we didn’t expect,” marking the very first documented instance of this X-to-autosome-to-Y chromosome movement followed by gene amplification on the Y.

The driving force behind this curious genetic journey is intimately linked with spermatogenesis—the process by which sperm cells mature. Since males possess one X chromosome inherited maternally and one Y chromosome from the paternal line, this generates sperm cells carrying either sex chromosome. During sperm maturation, the X chromosome temporarily assumes a role akin to an autosome, supporting genes essential for viability and sperm formation. Yet with only a single X chromosome present, evolution devised an alternative safeguard: duplicating critical genes onto the Y chromosome to serve as genetic backups, ensuring uninterrupted male fertility.

Mueller elaborates on this biological fail-safe, noting that “males carry just one X chromosome, so an evolutionary alternative method arose to back up critical sperm-creating genes.” Mier poetically likens this to “having your own clone ready to cover for you when you go on vacation,” underscoring the functional redundancy that guards against gene loss on the Y chromosome. This delicate balance is crucial because the genetic content of the Y must be preserved to maintain male reproductive success and, by extension, species survival.

A remarkable mechanism facilitating this genetic gymnastics involves transposable elements, often dubbed “jumping genes.” These elements are sequences within the genome capable of moving or copying themselves to new locations, silently nested in vast numbers, constituting nearly half of the human genome. The research team uncovered evidence that the deer mouse Phf8y gene commandeered the machinery of these transposable elements to replicate itself onto the Y chromosome. This molecular hijacking highlights the ingenious ways genomes innovate using their inherent mobile DNA sequences.

Despite cracking the code on how Phf8y journeyed across chromosomes and multiplied, the functional role of this gene family on the Y chromosome remains enigmatic. The researchers speculate that Phf8y may contribute to chromatin packaging during spermatid development—the tightly regulated process dictating how DNA is compacted within sperm cells. Such chromatin remodeling could confer a competitive advantage to Y-bearing sperm over their X-bearing counterparts, potentially influencing the sex ratio and reproductive success dynamically.

This revelation dovetails with previous studies in house mice, where similar genetic skirmishes between the X and Y chromosomes—sometimes described as an “arms race”—have been observed. These genomic conflicts drive rapid gene evolution and contribute to the differential selection pressures on sex chromosomes, further emphasizing the ongoing battle for dominance and survival at the genetic level.

Understanding these complex genomic interactions is not merely an academic exercise; it touches on fundamental biological questions about how the balance between males and females is evolutionarily regulated. If the mechanisms that preserve Y chromosome integrity falter, the ramifications could ripple through populations, disrupting the critical 50/50 sex ratio that underpins stable reproduction in mammals. Thus, insights gleaned from this research illuminate how gene mobility and amplification on the Y chromosome play a vital role in sustaining species continuity.

Moreover, this study presents a paradigm shift in how scientists perceive chromosome evolution, particularly regarding the fluidity of gene movement between chromosomes and how genomes innovate to counteract deleterious degeneration. The identification of Phf8y as an amplified retrogene family on the Y chromosome opens new avenues for research into genomic resilience, male fertility, and evolutionary biology.

The findings were the product of a collaborative effort involving researchers Ann Marie Lawson, Eden A. Dulka, T. Brock Wooldridge, and Hopi E. Hoekstra, highlighting the interdisciplinary nature of modern genetics research. Supported by prominent institutions, including the National Institutes of Health and the U.S. National Science Foundation, this initiative underscores the critical role of funding in advancing our understanding of complex biological systems.

In sum, the University of Michigan’s groundbreaking work unravels a novel example of genomic adaptability—demonstrating how a gene can traverse from the X chromosome to an autosome, and finally to the Y chromosome while amplifying itself to maintain essential functions in spermatogenesis. This not only redefines our understanding of the Y chromosome’s evolutionary narrative but also provides pivotal insights into the genetic foundations of male fertility and the maintenance of balanced sex ratios across mammalian species.

Subject of Research:
Evolution of the Y chromosome and gene movement mechanisms maintaining male fertility in mammals.

Article Title:
An X-to-autosome-to-Y chromosome amplified retrogene family functions in spermatids.

Web References:
http://dx.doi.org/10.1016/j.cub.2026.04.045

References:
Current Biology, DOI: 10.1016/j.cub.2026.04.045

Keywords:
Y chromosome, gene amplification, transposable elements, spermatogenesis, Phf8y, chromatin remodeling, sex chromosome evolution, retrogene, deer mouse, male fertility, genetic conflict, chromosome dynamics