In a new study published this week in the journal Scientific Reports, researchers from the Royal Botanic Gardens, Kew, working with partners in Africa and the UK, present a novel plant-host identification method that could help in the fight to reduce the transmission of infectious diseases such as malaria, through restricting the preferred plant food sources of mosquitoes.
Professor Phil Stevenson, Priority Leader of Trait Diversity and Function at RBG Kew, says: ‘Mosquitoes are some of the deadliest animals on the planet because they transmit many dangerous and lethal diseases including malaria. But what surprises many, is that mosquitoes have very high energy requirements which they satisfy from feeding on flower nectar, not just blood, and a good supply of nectar is important for mosquito abundance and disease transmission.’
The research shows that mosquitoes prefer to feed on sugar from certain plant species and an abundance of these plants in a disease-prone area could lead to higher mosquito populations and higher infection rates. In turn, scientists believe identifying and removing these plants from the landscape could help lower the disease transmission rates.
According to the World Health Organization, malaria and other mosquito-borne diseases are responsible for hundreds of thousands of deaths worldwide and is caused by parasite-carrying female mosquitoes feeding on human blood.
Furthermore, the current interventions of bed nets and spray insecticides are starting to fail in their effectiveness. What is needed are novel approaches to reducing mosquito populations during disease outbreaks and altering sugar sources in their habitat may prove to be a successful intervention.
Dr Amanda Cooper, postdoctoral researcher at the Royal Botanic Gardens, Kew, says: ‘Mosquito-borne diseases continue to challenge public health bodies throughout the tropical regions of the world. The main methods currently used to fight mosquito-borne disease, indoor insecticide application and bed nets, are becoming less effective as mosquitoes are building resistance. Thus, this new interventions for combating mosquito-borne diseases are desperately needed. We hope this work will be the start of finding new and effective interventions.
The study’s authors analysed the nectar chemistry of plants known to be used as a source of sugar by mosquitoes in areas where malaria transmissions are prevalent. They then identified unique metabolites from nectar inside the mosquitoes for more than eight hours after feeding, revealing which plants they have been feasting on.
While this can be done through DNA barcoding (by analysing the DNA of ingested plant material) it may be challenging to extract sufficient plant DNA from small nectar-eating insects. Instead, Kew’s scientists focused on nectar metabolites which provide a unique chemical character that can be used to distinguish different sources of plant sugars.
Three candidate species for the study were chosen from the vast living collections of Kew Gardens in West London that were also known to be ornamental plants grown in Bobo-Dioulasso in Burkina Faso. These were yellow sage (Lantana camara), castor oil plant (Ricinus communis), and yellow oleander (Cascabela thevetia), all of which are widespread throughout the tropics.
The Kew team are now hopeful their new approach could be used to screen plants in areas where mosquito-borne diseases are widespread, to help understand mosquito ecology and plant preference and possibly removing those plants from near to peoples’ homes, reducing the overall mosquito population numbers.
Prof Stevenson adds: ‘In this work we’ve developed a way of identifying which flowering plants mosquitoes prefer so that we can remove them from near people’s homes and reduce the abundance of the mosquitoes and the transmission of the diseases that that they vector. We think this could also be used to understand and influence the dynamics of infection in other important mosquito-borne diseases including dengue, Zika virus, and West Nile virus.’
Such studies are of critical importance, as infectious tropical diseases affect hundreds of millions of people globally each year. In 2022 alone, the World Health Organization (WHO) estimated some 249 million people were infected by malaria, with 608,000 deaths reported in 85 countries.
Found mostly in the tropics, malaria is caused by Plasmodium parasites carried by mosquitoes and can be entirely prevented by avoiding mosquito bites or with medication.
The research is part of a wider programme of work at Kew aiming to better understand the relationships between plants and invertebrates, particularly flower-feeding insects such as bees and other pollinators and small insects. The researchers are also keen to understand the role of nectar metabolites and how they affect animals.
Dr Cooper adds: ‘The only way to reduce the impact of mosquito-borne diseases is to find new avenues of targeting mosquito vectors and interventions through known host plants may be the solutions we need.’