Transcript Surprising Sentinels: Exotic egg parasitoid appears at Beltsville

Parasitoids of Brown Marmorated Stink Bug
(Halyomorpha halys) eggs: Comparison of three egg
mass types in three Maryland habitats.
Megan Herlihy1, Elijah Talamas2 and Donald Weber1
1USDA
2USDA
ARS, Beltsville, MD;
ARS, Washington, DC,
Introduction
• BMSB invasive pest from Asia.
• Many sentinel egg mass studies done,
generally reporting low rates of parasitism by
native parasitoids.
• Potential biocontrol agent parasitoids (family
Scelionidae) imported from Asia now in
quarantine for non-target testing.
Methods:
3 Habitat types
• Vegetable crop
(soybean)
• Orchard (apple)
• Woods near
stream (various
native and
invasive arboreal
and herbaceous
vegetation)
Methods:
3 Egg mass Treatments
• ≤24-hour old eggs laid by
colony insects
• ≤24-hour old eggs laid by
colony insects then frozen
at -80°C for 2 min.
• Screen cages (containing
20 BMSB and 1 bean
plant for oviposition)
– Provides the host finding
cues needed by parasitoids
– Cages are less labor
intensive/ time consuming
than searching for field laid
eggs as in Jones et al.
(2014)
Methods
Experimental design
• Fresh and frozen sentinel eggs laid on paper
towels by colony insects were pinned to various
vegetation at each site and were exposed for 72
hrs.
• Cage laid eggs were collected twice weekly.
(~ every 72hrs.)
• All egg masses returned to lab and reared out in a
growth chamber (16L:8D, 25°C) until either a
BMSB nymph or a parasitoid emerged
• If nothing emerged, eggs were dissected.
• Emerged and dissected parasitoids were sent to
Elijah Talamas (USDA ARS SEL) for identification
Methods:
BMSB eggs exposed by habitat and egg mass type
Total number of BMSB egg masses (# of individual BMSB eggs)
Hypothesis 1
• Frozen egg masses will result in higher rates of
successful parasitism than fresh or cage egg
masses at all sites, likely due to the lack of
immune defenses of the egg.
(we got this idea from Tim Haye of CABI in Switzerland)
Hypothesis 2
• Cage laid egg masses should result in higher
parasitism than 24-hour colony laid sentinel
egg masses, because it provides the
parasitoids with host finding cues.
Hypothesis 3
• Inclusion of wooded habitat
allowed us to find the exotic
Trissolcus japonicus,
previously thought to only
be found in quarantine in
the United States.
• Trissolcus japonicus is the
most successful parasitoid
to complete development
and emerge from live egg
masses.
Hypothesis 4
• Parasitoid species are habitat specific.
Hypothesis 5
• Native parasitoids are
only successfully
developing and
emerging from dead
eggs.
Hypothesis 6
• There is a seasonal pattern to the occurence
of parasitoids as a group or as individual
species.
Results:
H°1 Frozen egg masses will result in higher parasitism rates
Yes!
• Overall, frozen egg masses (25%)more likely to yield
adult parasitoids versus fresh (7%). (Fisher P p=0.000126)
1-tail
• Parasitoids more likely to develop to adulthood from
frozen (16%), versus fresh (4%) host eggs ( χ²=253 Pearson
p<0.0001)
• Parasitoids more likely to successfully emerge from
frozen (10%), versus fresh host eggs (3%) ( χ²=101.2 Pearson
p<0.0001)
Recovered parasitoid key
Results:
H2: Cage laid egg masses should result in higher parasitism
Because we used bean plants in all cages, we only saw Telenomus podisi in the cage treatments
Results:
H3: Trissolcus japonicus is the most successful parasitoid
Yes!
•T. japoncis is much
more successful at
emerging from fresh
egg masses than
native parasitoids.
(Fishers exact p<0.001)
•Native parasitoids are
more successful at
emerging from frozen
egg masses than T.
japonicus. (Fishers
exact p<0.001)
Results:
H4: Parasitoids are habitat specific
• Yes!
– T. japonicus and T. brochymenae found only in the
woods.
– T. podisi found only in the soybean field and in the
cages with bush beans.
– Anastatus sp. found only in the orchard.
– T. euschisti found in both the woods and the orchard.
Results:
H5: Native parasitoids are only successfully developing
and emerging from dead eggs.
• Can’t prove this yet, but…
19% of control eggs never emerged.
• This easily accounts for the 7% of egg masses
successfully parasitized by natives.
Results:
H6: There is a seasonal pattern
to the occurrence of parasitoids.
• Not enough data to tell.
Future research
• Expand the geographical
range where we place
sentinels and cages to define
the distribution of T.
japonicus.
• Improve the cage treatment:
Use sleeve cages on existing
vegetation in place of bean
plants.
• Include native beneficial
hemipteran egg masses in
future sentinel studies (e.g.
Podisus maculiventris)
2015 plan for sentinel egg mass detection of
Trissolcus japonicus and other parasitiods
Nearby sites BARC West: every week
North Farm original site (woods)
+ 4 additional woody sites
4 sites of orchard/savannah habitat
4 sites of field crop (soybean) habitat
BMSB reared, frozen, and Podisus
egg masses (3 plant hosts X 2 e.m.)
Satellite wooded sites: every four weeks, total 4 times during season
BARC South Farm (North area)
Linkage Farm (between RI Avenue and Metro yard)
frozen BMSB egg masses
Little Paint Branch North (north of Sellman Avenue)
only (3 plant hosts)
Beaver Dam Road (BARC East, west of BW Parkway)
Collaborator sites:
College Park, BARC East of BW Parkway, Port of Baltimore (UMd.)
Newark Delaware vicinity and other sites (ARS BIRL)
Area of Harpers Ferry & Northern Shenandoah (ARS AFRL & Va. Tech)
Acknowledgements
• Abby Rosenberg, Nate Erwin, Gabriel York and
Emma Thrift for their field work and other
help!