A new weapon to battle mosquitoes is taking shape in Welsh laboratories, and while researchers have some distance to go, the fatal fungus will also kill midges, ticks and sandflies.
Developed at the University of Swansea in Wales by an eight-member team headed by Professor Tariq Butt, Metarhizium anisopliae kills a wide range of insects, including most species of mosquito.
“The fungus can be broadcast or sprayed onto the water surface,” Professor Butt told the Caymanian Compass.
“The aquatic mosquito larvae ingest the spores whilst filter feeding. Pre-formed and secreted proteases from the fungal spores induce stress, leading to programmed cell death. We presume the insect cannot cope and dies,” he said.
Proteases are chemicals that break down larger molecules into their smaller components, in this case, essentially liquefying an insect’s internal organs.
“We have tested [the fungus] against species of Anopheles, Culex and Aedes,” Professor Butt said, referring to three typed of mosquito. “Larvae of all three genera are killed. However, Anopheles and Culex are more susceptible. These are killed within one day (depend[ing] on temperature and dose), Aedes takes slightly longer. We have tested the fungal strains against mosquitoes in Africa and Turkey with similar results.”
According to the Cayman Islands Mosquito Research and Control Unit, Cayman has 36 species of mosquito, Aedes taeniorhynchus, known as the “black salt marsh mosquito” is the most numerous among them.
“Most of our operational efforts go into the control of this species,” according to the MRCU website.
Two other aedes species, aegypti and albopictus, are widespread and can carry the yellow fever, dengue and chikungunya viruses.
The largest mosquito species in Cayman are Psorphora ciliata and Psorophora columbiae. While they do not carry disease, they hatch in large numbers after heavy rains, posing a serious biting nuisance.
Two species of the brown “Culex” mosquito breed in domestic settings, but pose little threat to humans, while one of Cayman’s several species of Anopheles, albimanus, carries the malaria parasite.
Alan Wheeler, assistant director of the MCRU, said he was “aware” of the fungus, but so far, remained partial to the “BTI” insecticide used by the unit.
The Bacillus Thuringienis bacteria are highly selective, killing only mosquitoes and close relatives like gnats and black flies, while leaving unharmed other insects, fish, birds, worms or mammals.
The Welsh fungus, he said, “is a biological control agent. We were hoping that, once the fungus went through a cycle, it would kill and go on to affect others.”
“It didn’t quite work out that way,” he said. “The fungus will take out only one insect and is very general.”
At this point, Mr. Wheeler said, “I would not want to replace BTI. The beauty of BTI is that it releases four different toxins, so it does not build up a general resistance.”
Metarhizium anisopliae is “another potential tool in the battle against mosquitoes,” he said, but BTI would remain his preferred poison. “It is very specific and it results in insect prevention.”
Professor Butt said his work came out of extensive efforts in the ‘70s and ‘80s to use fungus to control mosquito populations. “There is a renewed interest in these microbes because: (1) they offer an environmentally friendly alternative to chemical pesticides, (2) the fungus will kill both adults and larvae.
“The former are killed in the same manner as terrestrial insect hosts, i.e., adhesion of spores to the host cuticle [a tough but flexible outer covering of an organism], penetration of the cuticle using enzymes and mechanical force, colonization of the body cavity and [the proliferation of] spores taking place at the host surface.
He said his team had identified “several stains” of the Metarhizium fungus, all lethal to mosquitoes, and were working on improvements to bring multiple insects into wider contact with the pesticide.
“The strategies we are developing include use of ‘lures’ based on compounds adult mosquitoes find attractive, the goal being to attract the adult mosquitoes to the fungus,” he said. “The ‘lure and kill’ strategy is still in its infancy.”