Readers react to a revamped insecticide and a chronic pain biomarker

Pondering resistance

Microwaving deltamethrin can renew the insecticide’s ability to kill mosquitoes that have become resistant to it. Scientists are working to add the improved insecticide to bed nets, Tina Hesman Saey reported in “Restoring an insecticide’s mosquito-killing power” (SN: 6/17/23, p. 4).

Although the finding “sounds like a welcome discovery,” reader Linda Ferrazzara wrote, “might the newer, more effective version of the insecticide also have more serious adverse effects on the human beings it’s supposed to protect?”

Deltamethrin is so commonly used as an insecticide because it’s much more lethal for insects than it is for mammals, says Bart Kahr, a crystallographer at New York University. The lethal dose for a human, which is based on toxicology data for rats, would be more than 100 billion times what it is for a mosquito, he says.

Since microwaving deltamethrin changes its crystal structure but not its chemical composition, the lethal dose would not be expected to change, Kahr says. The new form might be faster at delivering deltamethrin to both humans and mosquitoes, but it would still take incredibly prolonged contact with a high amount of the insecticide to be consequential to a mammal. “Of course, no one has made such an experiment, but it stands to reason from the data that we have,” he says.

Understanding pain

Brain implants in four people with chronic pain revealed a potential biomarker of the debilitating condition. The brain signal could one day help doctors track treatment responses, Laura Sanders reported in “Implants track chronic pain in the brain” (SN: 6/17/23, p. 10).

Some readers on social media wondered what the discovery might mean for other types of long-lasting pain. “Am SO hoping that this will one day be expanded to those of us who have [the autoimmune disorder lupus],” Twitter user @SusanFi84657717 wrote. Meanwhile, Facebook user Wernell Loell hoped the finding might apply to pain associated with grief.

The study gave researchers a glimpse of just one specific type of chronic pain: neuropathic pain, which is rooted in the nervous system, Sanders says. Three people in the study had neuropathic pain after a stroke, and one person had phantom limb pain in an amputated leg.

“So far, researchers don’t have this detailed view of other types of long-lasting pain,” Sanders says. But the brain implant study, while small, has provided some hints. Scientists found patterns of activity in the brain shared by all four participants when their pain was high. But the research also turned up brain activity patterns that were unique to each person.

“Figuring out the neural signals — both common and unique — that come with various sorts of chronic pain is the first step,” Sanders says. “The bigger goal is to interfere with those signals. Scientists are now testing whether brain stimulation can short-circuit these particular pain signals.”


Ancient molecules tied to complex life” (SN: 7/15/23 & 7/29/23, p. 6) stated incorrectly that the oldest known eukaryotic fossils date to 800 million years ago. Instead, the sentence should say that the oldest known steroid fossils date to 800 million years ago. The oldest known eukaryotic fossils actually date to nearly 3 billion years ago.