The Problem Addressed and the Solution Pursued
The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is a polyphagous invasive pest from Asia that has had significant impacts on specialty crop production in the USA. Insecticide applications can protect affected crops from BMSB feeding injury but are not considered a long-term solution. As in its native Asian range, biological control of BMSB in wild and cultivated habitats may represent the ultimate resolution to this problem, although native natural enemies in the USA have not reduced BMSB populations adequately. Recently, adventive populations of Trissolcus japonicus (Ashmead), an effective egg Asian parasitoid of BMSB, were discovered in several locations in the USA, including Frederick County, VA. Consequently, determining the distribution and spread of T. japonicus, and its impact on BMSB populations, have become main research priorities. However, for several important reasons, current methods for T. japonicus surveillance, involving the production and deployment of BMSB sentinel egg masses and/or surveys for wild egg masses, are not efficient for use over larger geographic areas. The development of optimized sampling tools and protocols for T. japonicus surveillance and monitoring is paramount to all future efforts aimed at long-term sustainable management of BMSB. The goal of this project was therefore to develop and use an efficient, effective, and standardized protocol to address questions about where and when T. japonicus is present in the landscape.
- Examine and compare the effectiveness and efficiency of sentinel BMSB eggs and yellow sticky traps for sampling T. japonicus
- Determine the effect of habitat type on T. japonicus detections
- Determine the seasonality of T. japonicus detections
- Examine the effect of BMSB host tree species on T. japonicus detections
Objective 1. Examine and compare the effectiveness and efficiency of sentinel BMSB eggs and yellow sticky traps for sampling T. japonicus
Vertical Sampling Transects: This study was in 2017 in Frederick County, VA, where T. japonicus had been detected since 2015. Five mature female tree of heaven growing at the edge of woodlots adjacent to apple and peach orchards were selected for sampling. Trees were of similar height and architecture (i.e. had branches from bottom to top of the trunk). Eyebolts screwed into the top and bottom of the trunk of each tree had a closed loop of rope running through them, enabling sampling devices attached to the rope to be raised and lowered along the trunk as a vertical transect, with sampling locations at the lower, mid, and upper canopy of each tree.
Sentinel eggs and yellow sticky traps. BMSB adults were reared at Virginia Tech’s Alson H. Smith, Jr. Agricultural Research and Extension Center (AREC), Winchester, VA. Egg masses deposited on green bean leaves were collected daily and affixed to double-sided tape on a small piece of cardstock, then held at -80oC for ≤ 3 weeks before deployment in the field. Egg cards were affixed to the underside of leaves on excised shoot sections of female tree of heaven, which were inserted into 500 mL plastic bottles with water, then attached to the transect rope in each tree and positioned at the three canopy locations mentioned above.
In preliminary studies conducted in 2016, T. japonicus was captured in single-sided yellow sticky traps (Alpha Scents, West Linn, OR) deployed in the canopy of trees at the AREC. These were employed in 2017 for comparison with sentinel eggs. On alternating weeks from mid-May until late August, 2017, sentinel eggs or yellow sticky traps were deployed at lower, mid, and upper canopy locations in each tree. Egg masses were retrieved after 72-hr, since their attractiveness to parasitoids is known to diminish after that time. Egg masses were held in an environmental chamber and assessed daily for several weeks for emergence of parasitoid adults. On alternate weeks, yellow sticky traps were deployed in the same trees at the same canopy locations, and retrieved after 5 days. The parasitoids of interest (i.e. those considered to be potential parasitoids of BMSB) captured in traps and those that emerged from sentinel eggs were tentatively identified, then sent to a specialist for species confirmation.
The low numbers of adult T. japonicus captured or recovered from sentinel eggs in 2017 were not amenable to statistics, so results are presented using descriptive statistics.
Objective 2. Determine the effect of habitat type on T. japonicus detections
Field Sites: All study sites were in Frederick County, VA. Tree of heaven was again used as the model host tree. Trees (n = 1 per site) growing in the following common habitat types were selected; 1) spatially isolated patches associated with rock breaks in cultivated fields, 2) windbreaks or hedgerows, and 3) at the edge of woods (n = 5 per habitat type). The same sites and trees were used for T. japonicus trapping in 2018 and 2019.
Trapping Trissolcus japonicus
At each site, a double-sided, backfolding yellow sticky trap mounted atop a 4.8 m bamboo pole was suspended from a mid-canopy branch of female tree of heaven via a hook attached to the pole. Trap deployment at mid-canopy was informed by previous data showing that naturally-laid BMSB egg masses were most abundant in the mid- and upper tree canopy and that T. japonicus was recovered only from eggs collected from those locations. Traps were replaced at 7-day intervals from 3 May until 21 September, 2018 and from 20 April until 30 September, 2019. All parasitoids of interest captured were tentatively identified in situ, then sent to a specialist for species confirmation. Captures of T. japonicus each year were compared among habitat types using the Kruskal-Wallis test followed by the Bonferroni corrected Dunn’s test (SAS Institute, Cary, NC; SAS Institute Inc. 2018).
Objective 3. Determine the seasonality of T. japonicus detections
Data from Objective 2 were used to examine the onset, progression, and termination of T. japonicus captures in 2018 and 2019. For each year, weekly captures of male and female T. japonicus were pooled across the three habitat types.
Objective 4. Examine the effect of BMSB host tree species on T. japonicus detections
Field Sites and Tree Species: In 2017 and 2018, trees were sampled at the edge of woodlands in Frederick County, VA. In 2019, following the 2018 results from Objective 2, sampling was conducted in windbreaks. The yellow sticky traps introduced in Objective 2 were deployed in the mid-canopy of trees, as described previously. Selection of the tree species used was based on; 1) census data, 2) known hosts of H. halys, and 3) leaf architecture. Tree of heaven has been reported to be the most abundant species at the edge of woodlands bordering tree fruit orchards in this region, and as in our previous studies, was considered the standard host. The other species selected were black walnut, black locust, hackberry, and black cherry, and are also among the most common species recorded in a previous census. These trees represent a diversity of plant families and differ in leaf structure; tree of heaven, black walnut, and black locust have compound leaves, while hackberry and black cherry have simple leaves.
Simultaneous trapping in paired tree species at the forest edge: In 2017, tree of heaven was paired with black walnut, black locust, or hackberry (n = 5 per species pairing), with ≥ 10 m and ≤ 25 m between trees in each pair. One trap per tree was replaced at 7-day intervals from 31 July until 29 August, 2017. In 2018, the same trees were used again, and 5 pairs of tree of heaven and black cherry were added. Traps were deployed from 13 June until 20 September, 2018, and replaced at 7-day intervals.
Because trapping for T. japonicus in 2018 showed higher captures in female tree of heaven growing in windbreaks and isolated patches than at the woods edge, in 2019 traps were deployed in trees in windbreaks (n = 5 sites), each containing tree of heaven, black walnut, and black locust. Adjacent trap trees in each windbreak were 23.7 ± 8.6 m apart and the distance between the traps at the ends of the sampling area was 47.4 ± 15.9 m. Traps were replaced at 7-day intervals from 17 June until 11 August, 2019. As in the previous studies, all parasitoids of interest captured were tentatively identified in situ and subsequently sent to a specialist for species confirmation.
In 2017 and 2018, captures of T. japonicus were compared by species pair using a Wilcoxon signed-rank test, while in 2019 captures were compared among three host species using the Kruskal-Wallis test followed by the Bonferroni corrected Dunn’s test. All statistical comparisons used SAS (SAS Institute, Cary, NC; SAS Institute Inc. 2018) and were considered significant at P < 0.05.
Objective 1: In 2017, T. japonicus appeared to be relatively uncommon in Frederick Co., VA. Only one sentinel egg mass from mid canopy was parasitized by T. japonicus in (100% eggs parasitized), while three mid canopy traps and one upper canopy trap each captured one T. japonicus. Our finding that detections occurred only in the mid and upper canopy conformed with results from previous studies. Importantly, the time required for preparation, sampling, and processing sentinel egg masses was 590 X greater than required by sticky traps.
Objectives 2-3: In 2018 and 2019, the number of T. japonicus detected via this study increased markedly; 101 and 104 specimens were captured in the respective years. There was a significant effect of habitat type on T. japonicus captures (χ2 = 8.31, df = 2, P < 0.05); significantly more were captured in windbreaks than at the woods edge (z windbreak = 7.9, z woods edge = 6.9, P < 0.05). In 2019, there was not a significant effect of habitat type on captures (χ2 = 0.25, df = 2, P > 0.05). The seasonal period of activity of T. Japonicus in 2018 and 2019 was remarkably similar. In both years, the first capture was recorded in mid-May and captures were recorded on most weeks through mid- to early September. In both years, there appeared to be two periods when captures were highest, in about mid-July and about early August. Interestingly, these periods of peak captures tended to follow predicted periods of peak egg-laying by H. halys.
Objective 4: In this study, trapping for T. japonicus yielded 24, 42, and 13 in 2017, 2018, and 2019, respectively, possibly due to the different species of host trees used. In 2017, all captures of T. japonicus were from tree of heaven, but there were not significant tree species effects on captures for any host pairing; tree of heaven vs black locust, S = -3, P > 0.05, tree of heaven vs black walnut, S = -5, P > 0.5, tree of heaven vs hackberry, S = -3, P > 0.05. In 2018, 66.7% of T. japonicus were from tree of heaven, but again, there were not significant species effects on captures for any host pairing; tree of heaven vs black locust, S = -1.5, P > 0.05, tree of heaven vs black walnut, S = -10, P > 0.05, tree of heaven vs hackberry S = -11, P > 0.05, tree of heaven vs black cherry, S = -1, P > 0.05. In 2019, black locust, black walnut, and tree of heaven yielded 61.5%, 38.5%, and 0.0% of T. japonicus captures, respectively. In 2019, host plant significantly affected T. japonicus captures (χ2= 6.32, df = 2, P < 0.05). Significantly more T. japonicus were captured in traps in black locust trees (z black locust = 8.4, z tree of heaven = 7.3, P < 0.05), while captures in black walnut were not significantly different from those in black locust or tree of heaven (z black walnut = 7.8, z tree of heaven = 7.3, P > 0.05).
Educational & Outreach Activities
Education and outreach
Extension meeting for tree fruit producers: 5
AREC Open house 2018: Attendees: 200
New student tour 2018: Attendees: 15
Webinars, talks, and presentations: 15
Nov 2019 Quinn, N.F., Leskey, T.C., and Bergh, J.C. Oral. “Fantastic parasitoids of the brown marmorated stink bug and where to find them: The foraging ecology of adventive Trissolcus japonicus.” Department of Entomology Fall Seminar Series. Michigan State University. East Lansing, MI.
Oct 2019 Quinn, N.F., Leskey, T.C., and Bergh, J.C. Oral. “Fantastic parasitoids of the brown marmorated stink bug and where to find them: The foraging ecology of adventive Trissolcus japonicus.” Department of Entomology Fall Seminar Series. Kansas State University. Manhattan, KS.
Mar 2018 Quinn, N.F., Leskey, T.C., and Bergh, J.C. Oral. “Aspects of the foraging ecology of Trissolcus japonicus in Virginia.” Entomological Society of America, Eastern Branch Meeting. Blacksburg, VA
Mar 2017 Quinn, N.F., Leskey, T.C., and Bergh, J.C. Oral. “Searching for the samurai wasp and its host: Sampling Trissolcus japonicus and Halyomorpha halys in tree of heaven (Ailanthus altissima).” Entomological Society of America, Eastern Branch Meeting. Newport, RI.
Nov 2019 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. “Effect of trap color and host plant species on detections of Trissolcus japonicus (Hymenoptera: Scelionidae).” Entomological Society of America, Annual Meeting, Ten Minute Paper Competition. St. Louis, MO.
Jan 2019 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. “Habitat and tree species effects on Trissolcus japonicus (Hymenoptera: Scelionidae) detections in Virginia, USA.” International Organization for Biological Control, Lisbon, Portugal.
Nov 2018 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Oral. “Trapping Trissolcus japonicus in Virginia: Habitat and host plant effects.” Cumberland Shenandoah Fruit Workers Conference. Winchester, VA.
Nov 2018 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Oral. “Aspects of the foraging ecology of Trissolcus japonicus.” BMSB Working Group Meeting. Winchester, VA.
Nov 2018 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Oral. “Trapping Trissolcus japonicus in Virginia: Seasonal phenology and patch size effects.” Entomological Society of America, Annual Meeting, Ten Minute Paper Competition. Vancouver, BC.
Mar 2018 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Poster. “Development of an effective and efficient method for monitoring the presence and spread of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae).” Entomological Society of America, Eastern Branch Meeting. Annapolis, MD.
Dec 2017 Quinn, N.F., T.C. Leskey, and J.C. Bergh. Oral. “Assessing the presence and distribution of Trissolcus japonicus using yellow sticky traps.” Cumberland Shenandoah Fruit Workers Conference. Winchester, VA.
Nov 2017 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Oral. “Assessing the presence and distribution of Trissolcus japonicus using yellow sticky traps.” BMSB Working Group Meeting. Winchester, VA.
Nov 2017 Quinn, N.F., E.J. Talamas, T.C. Leskey, and J.C. Bergh. Oral. “The stratification of the brown marmorated stink bug (Halyomorpha halys) and its natural enemies in a common wild tree host. Entomological Society of America, Annual Meeting, Ten Minute Paper Competition. Denver, CO.
Sep 2019 Quinn, N.F. and W.T. Hadden. Oral. “Good bugs and bad bugs: Pests and natural enemies.” Loudoun County Public Library. Purcellville, VA.
Jan 2019 Quinn, N.F., T.C. Leskey, and J.C Bergh. Oral. “Samurai wasp: Update on an important new natural enemy of brown marmorated stink bug.” Mid-Atlantic Fruit and Vegetable Convention. Hershey, PA.
Workshops / field days: 2
Feb 2019 Quinn, N.F. Oral. “Master Gardener Entomology.” Gardening in Loudoun County Symposium, hosted by the Loudoun County Master Gardener Association, Virginia Cooperative Extension Office, Leesburg, VA.
Feb 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.
Quinn, N.F., E.J. Talamas, T.C. Leskey, J.C. Bergh. 2019 Sampling methods for adventive Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) in a wild tree host of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). J. Econ. Entomol. 112: 1997-2000.
The information on the biology and sampling of T. japonicus gathered as a result of the studies detailed here will inform future studies and help researchers evaluate T. japonicus populations in Virginia and beyond. As one of the most important biological control agents of H. halys, careful monitoring of their populations is essential. Surveillance programs informed by the data collected for these studies will be more efficient, increasing the likelihood of detection and improving our ability to target areas for T. japonicus release. Ultimately, our goal is to achieve widespread distribution of T. japonicus in Virginia, with the expectation that, as it does in Asia, will eliminate the threat from BMSB to growers, thereby enabling them to return to the sustainable management programs that were in practiced prior to the BMSB invasion.
Our work continues to reveal that T. japonicus has become well-established in Frederick County, VA. Consequently, its impacts on BMSB and the resumption of sustainable tree fruit pest management practices may be anticipated and will need to be monitored. Given that our other projects on T. japonicus surveillance and monitoring have indicated that it is either not present or present at undetectable levels elsewhere in Virginia, we have initiated a project to release and redistribute adventive T. japonicus more widely in the state. Preliminary indications, using our sampling approach, are that it is establishing elsewhere in Virginia, boding well for the resumption of sustainable tree fruit pest management throughout the Commonwealth.