Globally, Aedes mosquitoes cause ill health and deaths from dengue, yellow fever, and other arboviral infections. There is no effective vaccine for Aedes-transmitted diseases, so mosquito control remains the mainstay for their control. Semiochemicals play a significant role in modulating insect behaviour, so they are used to lure mosquitoes to their destruction or to repel them to halt infection transmission.

Now, researchers at the University of Nigeria, Nsukka, have said that palm wine is a potent source of semiochemicals that can be used to lure Aedes mosquitoes away from our environment. The odour of both the up-palm and down-palm wines repels them, according to a study in the Journal of Biological Research & Biotechnology Bio-Research.

In the new study, both up-palm and down-palm wines repelled mosquitoes consistently. Repellence increased as days passed: initially upstream mosquitoes ranged from 36.36 to 60 percent at the beginning, declining to 3.3–6.36 percent on the eighth day, whereas downstream ranged from 40–63.63 percent at the beginning to reach 93.63–100 percent on the eighth day.

In Nigeria, palm wine could be a cheap source of semiochemicals. It has, however, been reported to be attractive to Anopheles mosquitoes. Palm wines come from palm saps, which are allowed to ferment to some extent.

The sap is collected daily by wine tappers. In effect, what they obtain is palm sap that may age over approximately 24 hours. So even though they may be referred to as “fresh” palm wine, they contain some quantity of fermented products.

Organic compounds that can influence insects to react to them are referred to as semiochemicals. Mosquitoes perceive semiochemicals from the air with their organs of smell. Many other behaviours, like host location and locations where they lay their eggs, are determined by volatile semiochemicals.

Taking advantage of these behaviours, countermeasures against mosquitoes, such as luring them to kill or repel them, are explored owing to semiochemical exploration.

The researchers used the olfactometer to test the response of the mosquitoes to the odours from the up-palm and/or down-palm wine.

Between 10 and 12 adult female mosquitoes were introduced into the release chamber with the aid of an aspirator/sucking tube. Mosquitoes were allowed to acclimatise for five minutes in the air. Hereafter, the odours were introduced.

After 30 seconds, the mosquitoes were released from the chamber by rotating the mesh screen, thereby allowing them to escape from the chamber and make their choices: they were free to move towards the odour so that when they arrived at the confluence between the arms, they would make one more decision: to move to any one of the arms depending on how they respond to the preferred odour.

The alternative response was their freedom to move away from the odour by moving downstream. Thereafter, the number of mosquitoes was counted and categorised according to the part of the olfactometer they rested at the end of five minutes.

The experiment was carried out daily for eight days as follows: control (water) and up-wine; water and down-palm wine; and up-palm wine against down-palm wine. Each test was triplicated.

Aedes mosquitoes were not attracted to up-palm wine and down-palm wine for the duration of the study. Rather, they were repelled. The intensity of repulsion increased as the palm wines aged. The increased repulsion was marked by the mosquitoes moving more into the down section of the stem in the olfactometer.

The result apparently indicated that Aedes from the locality avoided palm wines, negating the response of flies generally to palm wine.

According to the researchers, “Our results suggest that the volatiles in the batch of palm wine used in this study may have suppressed/countered the known capacity of carbon dioxide to attract mosquitoes.

“This unusual finding may be an indication of genetic change or the unlikely event that the palm wines may have been compromised, as unscrupulous tappers and traders are known to use sundry products to modify palm wines sold in the market.

“Aedes mosquito repellence in this study was certainly due to palm wine volatiles. This observation is explained by the intensification of the production of volatiles, which increased as time went on.

“In the final experiment, where up-palm and down-palm wines were applied, both showed this repulsive property to Aedes mosquitoes, and their effect seemed to be additive. Increased repellence of mosquitoes by palm wines with time may be reflected in the increased fermentation occurring in palm wines that produce more chemical compounds, such as alcohol, that may be responsible for increased repellence with time.

“From these findings, palm wine could be used as a standard where other substances that have related effects could be compared.”

In reality, scientists have substantiated the use of plant products by humans to provide protection against biting insects and a variety of insect-borne diseases.

The different mosquito vectors exhibit contrasting responses to different chemicals and odours. As a result, there is a need for integrated sets of control methods that are tailored to the local environment. One such method is the use of palm wine, which can be made available to locals at a low cost and with ease. This, in turn, causes variations in the effectiveness of various methods in controlling local mosquito populations. (Nigerian Tribune)

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