60 Nebraskaland • March 2020
MIXED BAG
Emerald ash borer is an exotic, invasive insect that was
first confirmed infesting ash trees in Nebraska in June
2016. Since that time, the insect has been confirmed in
several counties in eastern Nebraska. Federal and state
quarantines are in place to prevent the spread of this pest
by regulating the movement of potentially infested wood
products. Regulated counties include Cass, Dodge, Douglas,
Lancaster, Saunders, Sarpy and Washington.
Significant research into biocontrol organisms as a means
of reducing the impact of ash borer infestations has occurred
in the United States in the last 15 years. Successful ash borer
biocontrol programs would reduce the survival of the insect's
eggs and larvae through parasitism by these biocontrol
organisms. While biocontrol will not eradicate EAB, it could
reduce the EAB population to the point that ash trees are able
to survive low level infestations. It may also protect ash trees
so that regeneration and canopy restoration can occur.
Biocontrol is proving to be a valuable tool to combat ash
borer infestations in parts of the U.S., and offers an exciting
opportunity to combat the pest in our state and help protect
Nebraska's ash trees.
In summer 2019, the U.S. Department of Agriculture
released three biocontrol wasps in Nebraska, targeting ash
borer. Though these small wasps love to attack ash borers,
they don't pose any risk to people. Oobius agrili parasitizes
ash borer eggs, while Tetrastichus planipennisi and Spathius
galinaea are larval parasitoids of the target insect. The
biocontrol insects were supplied by the USDA EAB Parasitoid
Rearing Facility in Brighton, Michigan. USDA selected sites
and made releases based on the USDA EAB Biocontrol
program guidelines.
It is too soon to know if the biocontrol releases in Nebraska
will be successful. However, the first two insects have been
widely released across other ash borer-infested states, and
research indicates those biocontrol wasps are becoming well
established. Oobius is reported to infest around 25 percent of
ash borer larvae at monitored release sites, while Tetrastichus
has been found parasitizing 20-80 percent of larvae. Spathius
galinaea has been confirmed infesting up to 50 percent of ash
borer larvae at release sites in Michigan and Connecticut. This
data suggests that successful establishment will be possible
in Nebraska, which is good news for the state's ash trees.
EAB BIOCONTROL
By Julie Van Meter, State Entomologist, Nebraska
Department of Agriculture
Oobius wasp, Tetrastichus wasp, Spathus wasp.
