The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is a polyphagous invasive pest responsible for severe crop losses. Native natural enemies and insecticides have not adequately reduced BMSB populations. Recently, an adventive population of Trissolcus japonicus (Ashmead), an effective parasitoid of BMSB from Asia, was discovered in Winchester, VA and several other locations in the USA. Even in states where T. japonicus has been detected, its distribution is unknown. Determining the presence and distribution of T. japonicus and its impact on BMSB populations has become one of the highest BMSB research priorities. Current sampling methods for sampling T. japonicus are inefficient and costly, hindering efforts to monitor its populations. The development of optimized sampling tools and protocols for T. japonicus is paramount to all future efforts aimed at long-term sustainable management of BMSB. I propose to develop efficient, effective and standardized protocols for sampling T. japonicus that ultimately will provide the information necessary to track its spread and impact on BMSB populations. As anticipated contributions of T. japonicus to enhanced biological control of BMSB in the USA are expected to enable a resumption of sustainable pest management in affected cropping systems, the need for an efficient and standardized protocol for monitoring T. japonicus is essential.
The spatial and host plant effects on the distribution and activity of T. japonicus are unknown, as is the true extent of its geographic distribution. I propose to develop efficient, effective and standardized protocols for sampling T. japonicus by examining:
1) The relative effectiveness of sentinel eggs and yellow sticky traps as sampling methods;
2) The effect of host plants on T. japonicus detection;
3) The distribution of adventive T. japonicus populations in Virginia.
Materials and Methods
Objectives. This project seeks to determine:
- the relative effectiveness of sentinel eggs and yellow sticky traps as sampling methods for japonicus
- the effect of host plants on japonicus detection
- the distribution of adventive japonicus populations in Virginia. Note that this objective has been modified for the upcoming field season to: “Determine the seasonal phenology and effect of patch size on T. japonicus detection.”
Note that this research was initiated in 2017, before the award performance period began.
Objective 1. The relative effectiveness of sentinel eggs and yellow sticky traps as sampling methods for T. japonicus
Vertical Sampling Transects. This experiment took place in Frederick County, VA, where T. japonicus was detected in 2015 and 2016. Five mature female tree of heaven of similar height and architecture were selected for sampling at the woods edge adjacent to apple and peach orchards. A professional arborist screwed one eyebolt into the trunk near the top of each tree and a second eye-bolt was attached near the base. Vertical sampling transects were created via a closed loop of rope through the eye-bolts at the top and bottom of the trees, enabling sentinel eggs and yellow sticky traps attached to the rope to be raised and lowered along the trunk. Sampling locations along this “pulley-system” transect occurred at the lower canopy, mid-canopy, and upper canopy of each tree.
Sentinel eggs. To rear egg masses for use as sentinel eggs, mixed sex groups of BMSB adults were held with food, water, and oviposition substrates in 30.48 cm3 Bug Dorm cages (BioQuip, Rancho Dominguez, CA) on metal shelves with overhead fluorescent lights in a dedicated room at 25oC, 70% RH, and a 16:8 L:D photo regimen. Cages were checked daily for egg masses, which were removed intact from the substrate and affixed to double-sided tape on a 3x5cm piece of cardstock. These egg cards were held in a freezer at -80oC for at least 24 hours but not more than 3 weeks before deployment in the field. The number of viable eggs in each mass were recorded and masses with fewer than 20 eggs were not used (BMSB females deposit a mean of 28 eggs/mass).
Egg cards were affixed to the underside of leaves on excised shoot sections of female tree of heaven using small plastic clothes pins. Shoots were inserted into 500mL plastic water bottles with water, and the bottles were attached to the transect rope and hoisted into the tree to the three elevations specified previously. Sentinel eggs were deployed every other week in 2017 from mid-May until late August. Egg masses were deployed for 72-hr periods during periods when the probability of rain and/or high wind was low. Sentinel egg cards were then retrieved. Egg masses with all or most eggs intact were held in an environmental chamber at 25oC and a 16:8 photoperiod and assessed daily for parasitoid emergence. Eggs that did not yield a parasitoid adult were dissected for evidence of incomplete parasitoid development.
Yellow sticky traps. From mid-May through late August 2017, sampling on alternate weeks using 23 x 14 cm one-sided yellow sticky traps (Alpha Scents, West Linn, OR) was conducted. Traps were deployed using the pulley-transects described previously, and on the same trees as sentinel egg masses, for 5 days/week. The number of adult Trissolcus japonicus recovered during each sampling interval and by each sampling method were compared using continuity adjusted χ2 (SAS 9.4, SAS Institute, Cary, NC).
Objective 2. The effect of host plants on T. japonicus detection
This experiment was also conducted in Frederick County, VA. Based on our preliminary data from 2016, which revealed recoveries of T. japonicus only from mid-and upper canopy of female tree of heaven and suggested highest recoveries from mid-canopy, in 2017 we focused these sampling efforts in the mid-canopy of a range of BMSB host trees (i.e. where naturally laid eggs might occur). Yellow sticky traps were deployed in the mid-canopy of the following pairs of host trees: 1) black walnut and female tree of heaven (n = 5 pairs), 2) black locust and female tree of heaven (n = 5 pairs), and 3) hackberry and female tree of heaven (n = 5 pairs). Trees within each pair were not closer than 10 m and not farther than 25 m apart. Yellow sticky traps were attached to a hook of semi-rigid wire at the end of 4.8 m bamboo poles and which were suspended over a branch of each host tree. Sticky traps remained in the field for 7 days from July 31st through August 29th for a total of 120 traps deployed. All parasitoids of BMSB were removed from the traps and identified.
Objective 3. The distribution of adventive T. japonicus populations in Virginia. Note that this objective has been modified for the upcoming field season to: “Determine the seasonal phenology and effect of patch size on T. japonicus detection.”
One woodland site next to commercial tree fruit orchards in Rappahannock, Loudon, Fauquier, Rockingham, and Nelson counties were selected for sampling in 2017. At each site, three yellow sticky traps were deployed at mid-canopy of female tree of heaven at the orchard-woodland interface, using the bamboo poles described previously. Traps were deployed for 7 days from August 23rd to September 8th (n = 54 traps deployed). All parasitoids of BMSB were removed from the traps and identified.
Results and Discussion
Trissolcus japonicus is still relatively uncommon overall, and few individuals were detected via sampling using vertical transects to compare sentinel egg masses versus yellow sticky traps (Objective 1). However, using this approach, 1 and 4 Trissolcus japonicus detections occurred via sentinel eggs and sticky traps, respectively. There was no significant difference between trapping methods (continuity adjusted χ2 (1, n = 255) = 0.263, P = 0.61) or canopy location (continuity adjusted χ2 (2, n = 255) = 1.63, P = 0.44) in the number of detections per sampling method.
In our paired host plant study (Objective 2), we there were 14 detections of T. japonicus in sticky traps, all of which occurred from female tree of heaven. This suggests a possible effect of host plant on T. japonicus foraging, which has implications for trap deployment for monitoring purposes.
Trissolcus japonicus was not detected in the other counties in which sampling was conducted, despite numerous detections in Frederick County during the same time period, suggesting that its current distribution and/or abundance in Virginia is localized.
Across methods, all detections of T. japonicus were from the middle and upper tree canopy, having important implications for monitoring the presence and spread of T. japonicus, as detection rates may be optimized by sampling higher in the tree canopy. The time required for preparation, sampling, and processing sentinel egg masses was 590 times greater than required by sticky traps. Data from sentinel eggs provide key information about the activity of H. halys natural enemies and are important for furthering our understanding of their effects in the invaded range. However, yellow sticky traps are a useful, low-input tool for monitoring the presence and spread of T. japonicus.
In 2018, our research will examine the effects of patch size and host plants on T. japonicus foraging ecology (Objectives 2 and 3), its seasonal phenology, and further delimitation of its distribution in Virginia.
Educational & Outreach Activities
EDUCATION AND OUTREACH
Curricula, factsheets, or educational tools: 0
On-farm demonstrations: 0
Online trainings: 0
AREC Open house: Attendees: 200
New student tour: Attendees: 15
Webinars, talks, and presentations: 4
March 2018 Quinn, N.F., Leskey, T.C., and Bergh, J.C. “Development of an effective and efficient method for monitoring the presence and spread of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae).” Poster. Entomological Society of America, Eastern Branch Meeting. Annapolis, MD.
Dec 2017 Quinn, N.F., Leskey, T.C., and Bergh, J.C. “Assessing the presence and distribution of Trissolcus japonicus using yellow sticky traps.” Cumberland Shenandoah Fruit Workers Conference. Winchester, VA. Attendees: 40
Nov 2017 Quinn, N.F., Leskey, T.C., and Bergh, J.C. “Assessing the presence and distribution of Trissolcus japonicus using yellow sticky traps.” Oral presentation. BMSB Working Group Meeting. Winchester, VA. Attendees: 40
Nov 2017 Quinn, N.F., Leskey, T.C., and Bergh, J.C. The stratification of the brown marmorated stink bug (Halyomorpha halys) and its natural enemies in a common wild tree host. Oral. Entomological Society of America, Ten Minute Paper Competition. Denver, CO . Attendees: 40
Workshops / field days: 1
February 2018 Quinn, N.F., and A. Acebes-Doria. “Master Gardener Entomology” Gardening in the Shenandoah Valley Symposium, hosted by the Northern Shenandoah Valley Master Gardeners Association, Shenandoah University, Winchester, VA. Attendees: 50
Manuscripts in prep: 1
Title: Vertical stratification of brown marmorated stink bug (Halyomorpha halys) life stages and parasitoids in wild tree hosts
Authors: N.F. Quinn, E.J. Talamas, T.C. Leskey, J.C. Bergh