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Researchers at UC Riverside have demonstrated how ammonia and amine odorants could be used to combat insect-driven diseases, such as Malaria and Dengue Virus. New research by scientists at the University of California, Riverside, has potential in insect control through volatile repellents that could be applied on surfaces such as windowsills, eaves of huts, house entryways, backyards, outside produce storage areas, entryways of livestock shelters, and next to crops in a field. The first research paper is titled, “Chemosensory detection of aversive concentrations of ammonia and basic volatile amines in insects,” and it appears in the journal, iScience. The second research paper is titled,  “Pentylamine inhibits humidity detection in insect vectors of human and plant borne pathogens.” 

The researchers first focused on ammonia, a basic volatile compound found in insect environments. At low concentrations, such as in human sweat, ammonia is an attractant for mosquitoes and other insects but, at high concentrations, such as in household cleaners, ammonia is no longer attractive. The researchers inquired into what happens to the olfactory system, or smell, and gustatory system, or taste, of fruit flies and mosquitoes in the presence of ammonia.

Anandasankar Ray, a professor of molecular, cell and systems biology, who led the studies described the science behind this phenomenon, “We found the olfactory neurons seem to have a burst of activity and then they become silent for a while. During the silent period, the neurons are not able to detect any odorants, which means insects cannot effectively find human skin odor.” 

When Ray’s team tested the taste system of fruit flies and mosquitoes (Aedes aegypti), they found a similar response. “Where taste is concerned, we found ammonia and ‘amines’ derivatives of ammonia that make up many synthetic odorants don’t produce the flash type of activity we see in the olfactory system,” Ray explained.

According to Ray, the discovery could be used to make effective insect repellents in the future. 

“While compounds like ammonia, which have a high pH and are basic, cannot be used on skin due to their corrosive properties, they can be used in other ways. Many biting insects fly into homes from outside. In most parts of the world, insects bite humans and pets indoors and often at night.” He explained how the repellents can be applied on a variety of surfaces, “For example, if walls, where insects land and wait, had a high pH material in them, mosquitoes would be affected. Similarly, if a high pH compound, such as an amine, were dispensed around entryways of homes and animal sheds, it could keep mosquitoes away.”

In the second research paper, Ray’s lab studied behavior modification to humidity in the Asian citrus psyllid, an insect which transmits citrus greening disease, as well as mosquitoes. The lab discovered that amine odorants inhibit the humidity response. Ray explained, “We identified neurons in the ACP that detect humidity and found that certain amines could inhibit their humidity sensing. We then showed this was conserved in fruit flies. This is probably the first time that researchers have shown that humidity sensing can be inhibited by odorants.”

“This means that by blocking the insects’ ability to sense water using a volatile odorant, we can manipulate their humidity sensing pathway and alter their behavior in a predictable manner,” Ray said. “In the future it may be possible to engineer amines to prevent insect egg laying in certain areas.”

Insect-driven diseases are prevalent worldwide with about 241 million cases of malaria occurring worldwide in 2020, with a few more million cases occurring in 2021. Third world countries are especially impacted as nearly half the world’s population lives in regions where contracting malaria and dengue are risks. In addition, insects are often pears who destroy a third of agriculture.