September 2022 - 6

SWD-killing wasps released in Michigan to protect fruit
By Gary Pullano
FGN Senior Correspondent
Michigan State University (MSU)
researchers who specialize in fruit crop
pests have begun testing the effectiveness
of a new biocontrol agent that could help
reduce the damage caused by spottedwing
drosophila (SWD) on crops.
This invasive pest has been one of the
top production challenges for berry and
cherry growers in recent years since it
arrived in the United States. The samba
wasp (Ganaspis brasiliensis) is a tiny
parasitic wasp that lays its eggs in
SWD larvae.
After years of evaluation and
permit review, the U.S. Department of
Agriculture (through its Animal and
Plant Health Inspection Service) and the
Michigan Department of Agriculture and
Rural Development have approved release
of this wasp in regions where it threatens
fruit production.
One of the MSU researchers, Juan
Huang, traveled in April to the USDA lab
in Delaware and received training on the
rearing process. She returned to MSU with
100 of these insects to begin mass-rearing
efforts. Sufficient numbers of wasps are
now in colony, with releases having taken
place recently for cherries at the Northwest
Michigan Horticulture Research Center
in Traverse City, Michigan, and on Aug.
18 for blueberries at the Southwest
Michigan Research and Extension Center
(SWMREC) in Benton Harbor.
The researchers will assess the impact
of this new species on SWD populations
and their potential for establishment
in Michigan's climate. This program
provides hope for improved integrated
pest management practices on fruit farms
across Michigan and the potential to
reduce their potential for establishment
in Michigan's climate. This program
provides hope for improved integrated
pest management practices on fruit farms
across Michigan and the potential to
reduce insecticide spraying for this pest.
" This tiny little wasp is flying around
looking for berries that are infested already
with spotted-wing drosophila larvae, " said
MSU entomologist Rufus Isaacs.
Isaacs, lab manager Jackie Perkins and
Integrated Pest Management Educator
for fruits and vegetables for southwest
Michigan growers, Michael Reinke,
released three vials of the samba wasps in
a SWMREC test plot of Elliott blueberries
on Aug. 18.
" A lot of that will be in wild habitat
around the farms, " Isaacs said. " Their job
is to find a blueberry that's infested with
SWD larvae. They will stick their egg
layer into the berry, which contacts the
inside of the SWD larvae, and they will
then lay their egg into the fruit, inside
the spotted-wing drosophila larvae. And
then it develops on the inside, killing
that larvae, and comes out as a wasp in
about a month. "
Issacs said the wasps are then going to
mate. Each wasp should lay approximately
60-80 eggs.
" We've already been monitoring the
percentage of native wasps in this field
6 | FruitGrowersNews.com
A vial of samba wasps prepared for
release in a blueberry field.
Photos: Gary Pullano
this summer, " he said. " Now, we've
done these releases and will be coming
back here to see if we can recapture
this emerging out of the spotted-wing
drosophila population here and in the
other sites we're doing the releases for. "
It took years of evaluating many kinds
of wasps to see which one would deliver
the best results.
" This one was selected and then went
through jumping through the hoops that
you have to do to get the testing done,
including approvals from USDA-APHIS, "
Isaacs said.
" There is already detection of this wasp
species in Washington state, so they're a
little bit ahead of us. By doing this we are
hoping everyone can catch up. "
The MSU researchers are releasing the
wasps in Trécé Inc. SWD traps, which
provide a dispersal point for the wasps to
move into the blueberry bushes.
The traps hang in the bush part of
the plant, placed far enough in so that
workers don't knock them off when
coming through with equipment.
When Reinke pulled the plug on the first
vial of wasps, an SWD fly conveniently
landed on the trap, providing a proof of
concept-type realization.
" This tiny little wasp is
flying around looking for
berries that are infested
already with spotted-wing
drosophila larvae. "
− Rufus Isaacs, MSU
" We can be a little ceremonial with it, "
Perkins said. " The process for rearing
these is quite complicated. You have
to have fresh fruit. You have to have
a colony of (SWD) flies to access that
fruit. You have to transfer wasps using
an aspirator-type device. Each individual
wasp to get sucked up with an aspirator
and transferred on to that infested fruit.
You leave them on the fruit for 5-7 days.
Once they've laid eggs into that larvae,
you transfer them on to the next stage of
infested fruit. "
MSU student Andrew Jones has been
handling most of that process, and the
specific conditions, such as humidity, has
been a learning process for everyone in
the project.
From left, Michigan State University (MSU) Integrated Pest Management Educator
for fruits and vegetables for southwest Michigan growers, Michael Reinke; MSU
entomologist Rufus Isaacs and lab manager Jackie Perkins prepare to release three
vials of the samba wasps in a test plot of Elliott blueberries on Aug. 19.
" It's the end of a long journey to get
here, but it's also just the start of being
able to see how they work, " Isaacs said.
A national effort
Collaborating researchers recently
released the wasps in selected West Coast
locations hoping they'll establish and help
control the SWD.
" In Michigan, we're doing it here and
in Traverse City with cherries and other
researchers all across the U.S. are doing
trials in other states and other settings, "
Isaacs said. " That group of entomologists
across the country will be comparing notes
and seeing where it establishes well and
where does it reduce SWD populations.
That will take years to measure the longterm
benefits of the (wasps). "
The wasps are being released at some
unmanaged sites where they won't be
sprayed, to give them a better chance
to establish a population. Releases at
commercial sites could start in the fall,
Isaacs said.
He acknowledged it will be a long
process to bring the wasps to growers on a
regular basis.
" We're still trying to improve the
rearing methods to make it easier than it
currently is, " he said. " In farms, the release
will be more likely in the woods and wild
habitat where you've got this reservoir of
spotted-wing drosophila coming into the
farms, partly because growers are spraying
to protect the fruit from spotted wing
drosophila and these (wasps) are very
sensitive to pesticides.
" At the moment we're thinking maybe
an early season release that you might do
to kick-start biocontrol for this pest in the
spring, " he said. " Then releases would be
going on through the summer, primarily
in the wild areas to try to reduce the
invasion that you keep getting from the
edge of the fields.
While there are commercial insectaries
that raise biocontrol agents, Isaacs said,
it's undetermined whether a commercial
distributor will supply the program.
Widespread application
The samba wasp will go on any fruit host
where spotted-wing drosophila exist. As
the pests move to different hosts over time,
" the wasps will hopefully follow those, "
Isaacs said.
" It's a very active area of research.
Some labs are already planning and
overwintering study of these wasps.
We will see how well they survive the
Michigan winter.
" We have good habitat on the west
side of the state, " Reinke said. " We have
good snow cover that will protect them
over the winter.
Isaacs said the original funding for much
of the discovery work came from Specialty
Crop Research Initiative (SCRI) funding to
California, Oregon and Washington.
" We've had more recent SCRI grants that
have helped us continue the biocontrol
evaluation and all of the work that had to
be done to get to the point of having an
approval for release, " he said.
The Michigan Department of
Agriculture is funding the program
through a specialty crop block grant,
as well as the Michigan Blueberry
Commission. Project GREEEN funding is
paying for the work to ramp up the wasp
population. FGN
Samba wasp vial prepared for release in an SWD trap.
http://www.FruitGrowersNews.com
September 2022

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