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 Nature Biotechnology University of Maryland
entomology professor Raymond St. Leger and Chengshu Wang 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,"
St. Leger said. "A scorpion kills by stabbing its prey, so we were looking
for a way to get the toxin into the insect without the scorpion.

"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."

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.

"The problem is it takes quite a few fungal spores to kill the
mosquito, and it is slow," St. Leger said.

"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 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 other
circumstances."

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 species.


[www.biotechnews.com.au]