University of Maryland entomology professor Raymond St.
Leger has discovered how to use scorpion genes to create a
hypervirulent fungus that can kill specific insect pests, including
mosquitoes that carry malaria and a beetle that destroys coffee crops,
but does not contaminate the environment as chemical pesticides do.
In the November issue of the journal Nature Biotechnology, St. Leger
and Chengshu Wang, a colleague from the Chinese Academy of Sciences,
describe how they were able to bioengineer a new version of the fungus
Metarhizium anisopliae to inject specific insects with the scorpion
toxin Androctonus australis insect neurotoxin (AaIT), and kill them
within a few days.
“Scorpions have toxins that are superbly adapted to killing
insects,” explains St. Leger. “A scorpion kills by stabbing its prey,
so we were looking for a way to get the toxin into the insect without
“Fungi are really good at that because they are naturally infective.
They land on the insect’s outer surface, insert little tubes called
hyphae, and grow within the insect. You could almost see them as tiny
hypodermic needles. If you can get the fungus to insert a toxin into
the insect, you can kill the insect very quickly. This is what we did.”
Speeding up the Process
The naturally occurring M. anisopliae fungus and other strains like
it are already being used to control agricultural pests and mosquitoes,
but their effectiveness has been limited in comparison to chemical
pesticides. Unlike chemical pesticides, these altered fungi can be used
to target specific insects and do not pose a threat to the environment.
In Australia, the fungus is sprayed from airplanes to target locusts
and grasshoppers that decimate food crops. In Africa, the spores of the
M. anisopliae fungus are put on sheets and hung inside houses to kill
mosquitoes. “The problem is it takes quite a few fungal spores to kill
the mosquito, and it is slow,” says St. Leger. “It reduces the number
of mosquito bites that people get, but it doesn’t keep people from
getting malaria or dengue. We’re trying to get a supercharged,
hypervirulent fungus that will take out the mosquitoes quickly.”
St. Leger also is looking at the possibility of using the enhanced
fungus to attack the coffee berry borer, an invasive beetle that causes
severe damage to organic coffee crops in Colombia and other parts of
Latin America. After oil, coffee is the largest legally traded
commodity in the world, so the industry is eager to develop
biopesticides that will protect the crop.
To produce the insect-killing fungus, St. Leger created a synthetic
scorpion gene which he inserted into the M. anisopliae fungus. “You
can’t just take out the scorpion gene and put it into the fungus. You
have to turn that piece of DNA into something that the M. anisopliae
can use properly,” he explains.
He also had to create what he calls an “on/off switch” in front of
the gene so the fungus will produce the scorpion toxin only when it is
in the blood of the insect. “The fungus will never produce it under any
St. Leger tested the infectivity of the transgenic fungus against
mosquitoes, caterpillars and the coffee borer beetle. It was nine times
more virulent than the wild M. anisopliae in killing mosquitoes, 22
times more virulent to caterpillars, and 30 times more virulent to the
coffee borer beetle.
St. Leger believes this supercharged, pathogenic fungus has great
potential to become a cost effective biopesticide that can kill using
far fewer spores than the wild M. anisopliae fungus. He is currently
using a range of genes, including scorpion toxins, to create additional
biocontrol agents that are also highly specific to important pest
The journal article is entitled “A scorpion neurotoxin increases the potency of a fungal insecticide.”
University of Maryland, College Park. November 2007.