October 2022 - 20

CHERRY MARKETING INSTITUTE
Mighty but tiny samba wasp SWD natural enemy
JULIE GORDON
President/
Managing Director
JGordon@usacherries.com
The Michigan Cherry Committee has
put forward the 2023 cherry industry
research priorities for Michigan State
University and Project GREEEN. Spotted
wing drosophila (SWD) remains on the
top of the list.
Since its accidental introduction and
first detection in Michigan in 2010, SWD
has become one of the biggest threats to
berries and cherries close to harvest. This
pest rapidly reproduces with each female
capable of laying up to 350 eggs over
their lifespan, completing their life cycle
from egg to adulthood in as little as 8-10
days, with many overlapping generations
possible in a single season.
Unlike native drosophila species that
rely on rotting or damaged fruit, this
pest uses its saw-like ovipositor to cut
into intact thin-skinned fruit to insert
their eggs. The fruit is destroyed as
larvae feed from within. Insecticides
targeting adult flies have been the main
line of defense available to protect fruit
from infestation close to harvest. This
has put a tremendous strain on our tart
cherry industry.
There are natural enemies of
drosophila flies. These are mainly
tiny wasps called parasitoids that lay
their eggs in either larvae or pupae of
drosophila flies. However, our native
parasitoids are not adapted to SWD
and are unable to survive to adulthood
when SWD is their host.
In 2013, a group of scientists affiliated
The tiny samba wasp, a natural enemy of
spotted wing drosophila, has been released
in Michigan. Photo: Hannah Burrack
with the USDA-Agricultural Research
Service began exploring the native host
range of SWD in Asia with the goal
of finding effective natural enemies of
this important pest. One species they
found is now called the samba wasp. It
is a tiny little wasp that can detect SWD
larvae in fruit, and lays its eggs inside
SWD larvae, eventually destroying the
SWD host as it develops.
These tiny biological control agents
have been studied in quarantine facilities
to determine their efficacy against SWD,
whether they meet the criteria for host
specificity, and whether they can be
mass-reared for eventual release against
populations of SWD. A successful
petition to USDA's Animal and Plant
Health Inspection Service has allowed
for the first round of coordinated,
controlled releases of the samba wasp in
thirteen U.S. states, including Michigan.
A sentinel trap used to monitor for parasitoids in a wooded edge of a cherry orchard in
Michigan. A small deli container with a mesh lid contains fruit pre-infested with SWD
larvae, protected from the elements in a delta trap. Photo: Julianna Wilson
Because SWD attacks ripening
fruit of both wild and cultivated hosts,
this biological control agent has the
potential to help suppress populations
of SWD in habitats beyond our
cultivated plantings. In the summer
of 2022, the Wilson and Isaacs Labs
in the Department of Entomology
at Michigan State University have
released the samba wasp in wooded
edges of three commercial cherry and
blueberry plantings, immediately after
harvest when infested fruit is abundant,
with the hope that they will establish
themselves here in Michigan. We are
monitoring their success with sentinel
traps and plan to do more releases and
monitoring in the 2023 field season.
In August, U.S. Sen. Gary Peters
(D-Mich.) introduced the SWAT Act to
create a fund within APHIS specifically
for the research and mitigation of
SWD, funded at $6.5 million each
year for five years! The Act is cited
as the Spotted Wing Abatement
Trust Act of 2022 or the SWAT Act
of 2022. Pooling resources, targeting
our research program and leveraging
funds are critical to the management of
this threat. Special thanks to Senators
Peters, Mike Braun (R-Indiana)
and Susan Collins (R-Maine) for
introducing the SWAT Act.
The tart cherry industry would also
like to extend a special thank you to
Michigan State University assistant
professor of tree fruit entomology
Julianna Wilson and MSU Extension
Agent Nikki Rothwell for their
dedication to SWD research over the
years, as well the many researchers,
extension educators, IPM Alliance team
members and others who have helped
navigate the challenges of SWD. FGN
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October 2022

Table of Contents for the Digital Edition of October 2022
