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 ARS, Beltsville, MD; 2USDA 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)

MethodsExperimental 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

ratesYes!

• Overall, frozen egg masses (25%)more likely to yield adult parasitoids versus fresh (7%). (Fisher P1-tail p=0.000126)

• 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 weekNorth Farm original site (woods)

+ 4 additional woody sites 4 sites of orchard/savannah habitat 4 sites of field crop (soybean) habitat

Satellite wooded sites: every four weeks, total 4 times during seasonBARC South Farm (North area)Linkage Farm (between RI Avenue and Metro yard)Little Paint Branch North (north of Sellman Avenue)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)

BMSB reared, frozen, and Podisus egg masses (3 plant hosts X 2 e.m.)

frozen BMSB egg masses only (3 plant hosts)

Acknowledgements

• Abby Rosenberg, Nate Erwin, Gabriel York and Emma Thrift for their field work and other help!