The malaria-causing mosquitos have found a new safe haven in an invasive plant previously known to be habitat in South and North America.
Researchers from Kenya-based International Centre of Insect Physiology and Ecology (icipe) say they have generated new evidence of the immense threat posed by a highly destructive invasive plant, known scientifically as Parthenium hysterophorus.
They say the invasive plant believed to have entered East Africa through Ethiopia could be linked to the probable escalation of malaria incidents in East Africa.
The researchers in a study published mid-last month (https://rdcu.be/cpfvh) said the weed, nicknamed ‘famine weed’ due to its phenomenal adverse impact on people’s health, agriculture, livestock and the environment, has contrastingly favourable effects on Anopheles mosquitoes, which transmit the malaria parasite.
Also, the researchers note the possibility of exploiting the Parthenium-mosquito relationship to control the insects whose effects immensely contribute to Africa disease burden.
“In general, mosquitoes lay their eggs in standing water. However, we have established that Parthenium releases from its roots, chemicals known as terpenes that have a distinct blend of mosquito-attractive fragrances. When these chemicals leak into stagnant water, they enhance its attractiveness as an egg laying site for mosquitoes, in comparison to plain water,” explains Prof. Baldwyn Torto, Head, icipe Behavioural and Chemical Ecology Unit (BCEU).
Professor Torto said their research further demonstrates that preference has major implications on the ability of mosquitoes to survive and thrive.
The Parthenium root chemicals enable mosquito larvae to emerge two to three days earlier, and they also extend the lifespan of the adult mosquitoes arising from the contaminated breeding sites to a week longer than normal, thus boosting their chances to bite people and transmit the malaria parasite,” he said.
These findings are especially significant considering that Parthenium – a native of North and South America and one of the world’s most devastating invasive plants – is widely spread across East Africa including in flooding-prone malaria endemic zones.
Parthenium aggressively colonises its invaded regions, killing other plants and reducing crop yields. It also produces a highly toxic compound called parthenin that causes dermatitis, hay fever and asthma in people, poisons animals and contaminates meat and dairy products in livestock that has fed on it.
Farmers in Ethiopia named Parthenium hysterophorus: “Faramsissa,” or “sign your land away” because of its colonizing nature with to wipes out other biodiversity.
In 2015, icipe published a seminal study that made the first global connection between Parthenium and mosquitoes. The research demonstrated that the weed is a preferred nectar source for Anopheles mosquitoes and it can sustain these insects by extending their lifespan even in the absence of a blood meal from people.
Researchers also found that the female Anopheles mosquitoes that feed on Parthenium survive longer, accumulate substantial energy reserves and they are capable of laying more eggs.
“Importantly, the researchers found that parthenin does not have the same toxic effect on adult female mosquitoes as it does on people and animals, indicating that the insects can tolerate and possibly detoxify themselves of the compound” reads part of the findings.
Prospective solutions
“Our recent findings present a silver lining in that the chemical fragrances found in the roots of Parthenium could be used as a bait in combination with traps, to selectively capture pregnant female mosquitoes seeking egg laying sites,” explains Trizah Milugo, a Kenyan student who conducted the study as part of her PhD research based within the icipe BCEU.
“We also noted that only half of the eggs deposited in water containing these chemicals hatched. We singled out parthenin as being responsible for the low egg hatch rate, meaning that female mosquitoes can compensate the cost of exposing their juveniles to plant toxins for improved survival as adults.”
“Globally, invasive species are considered one of the most important perils to nature due to their severe impact on many socio-economic aspects,” notes Dr Segenet Kelemu, icipe Director General & CEO.
“Africa is one of the most susceptible regions, with a long and diverse list of such menace. Therefore, icipe has prioritised the management of invasive species as a key area of focus.”
Studies have found that a single mature Parthenium plant produces a minimum of 25000 and a maximum of 100,000 seeds The seeds are then dispersed by vehicles, wind, water, machinery, animals, and along with fodders and grains.
Parthenium hysterophorus was in 2015 identified by NEMA as one of the dangerous invasive plants in Uganda. The national biodiversity strategy 2015 -2025 list among the invasive plants threatening biodiversity.
But it is common to find the wed thriving along the roads side. Studies within Uganda indicate that it may have invaded the country less than a decade ago.
It was first identified at Bugembe and Mbikko near Jinja in 2008. It has since 2010 been listed among the top invasive plants devastating Queen Elizabeth National Park poisoning cattle, buffalos and antelopes. It reportedly causes allergic reactions in humans after prolonged contact.