Mosquito repellants from orchids .. Less toxic and more effective

Tariq Kabil

A team of researchers led by Washington University professor of biology Jeffrey Revell has discovered chemical signals leading mosquitoes to pollinate specific types of orchids flowers.

Their research, published in the "Proceedings of the National Academy of Sciences" on January 7, 2020, states that orchids produce a balanced package of chemical compounds that stimulate the mosquito's sense of smell.

Some of these chemicals have attractive or repressive effects on mosquitoes, and new research findings can help develop less toxic mosquito repellants, more effective traps, and an understanding of how the mosquito brain responds to sensory information, including signals that, at times, bite female mosquitoes One without the other.

The smell of orchids
The prevailing belief that all mosquitoes feed on blood is a misconception. Only females without males absorb the blood of animals and birds and need it to produce eggs. They thus transmit diseases and epidemics. As for males from them, they only feed on the extract of flowers.

"Nectar is an important source of food for all mosquitoes ... For male mosquitoes, nectar is the only source of food, while female mosquitoes feed on nectar throughout their life with the exception of a few days," said Revell, the lead author of the study, to the University of Washington News website.

However, scientists know very little about the scents that attract mosquitoes to specific flowers, or repel them from other flowers.

Acute orchid plants are widespread in most cold regions of the northern hemisphere, and Revell's team has investigated previous research that showed that local mosquitoes only pollinate this type of flower, and do not approach their wild relatives who grow in the same habitat in Okanogan Forest Wenatchee National in Washington State.

When the researchers covered the flowers, mosquitoes fell on the flowers covered with bags of fabric, and tried to feed on the nectar through the cloth. To find out the reason, the Revell team resorted to preparing the individual chemicals that make up the scent of orchids in the same proportion, and mosquitoes were affected as effectively as they were by the scent of real flowers.

"The smell is actually a complex mixture of chemicals - the smell of the rose consists of more than 300 chemicals - and mosquitoes can detect every type of chemical that creates the smell," Ravel says.

Revell's team also showed that a chemical illuminates the same area of ​​the mosquito's brain that is affected by the famous DEET mosquito repellent.

"Our results show how environmental signals from flowers can stimulate the mosquito's brain as much as the warm-blooded host ... and it can pull mosquitoes toward a target or send them in another direction," Revell said.

Access to catalytic chemicals
The team used gas chromatography and mass spectrometry to identify dozens of chemicals, and compared to their relatives, the smell of orchid contained large quantities of a compound called nonanal, and smaller amounts of lilac aldehyde.

Revell's team also recorded electrical activity in mosquito-sensing pods that detect odors. Both substances stimulated the electrical activity of mosquitoes that return to the habitat of orchids with sharp leaves, mosquitoes Anopheles Stephenie, which spreads malaria, and the Aedes aegypti that publishes dengue, yellow fever, zika and diseases Other.

They also viewed the brains of Aedes aegypti mosquitoes, and photographed calcium ions, that is, the signature of neurons in the region that processed the signals of the sensor pods.

EEG experiments revealed that nonunal and lilac aldehydes stimulate different parts of the lobe of mosquito sensing pods. According to Rayville, orchids with sharp leaves have a mosquito attract ratio, while closely related plant species do not.

The team also discovered that lilicdehyde stimulates the same area as the lobe of the mosquito-sensing pods, such as the mosquito repellent "Diet".

According to Revell, it is too early to know whether lilacdehyde may one day be an effective mosquito repellent, and more research is necessary to verify this. If confirmed, an added bonus is that it "smells wonderful," said Revell.