The introduction of the predatory Giant Asian Hornet, Vespa mandarinia Smith, to North America in 2019 has motivated efforts to create early detection systems for this and other non-native social wasp species (Hymenoptera, Vespidae). Various trap and bait combinations have been used for this purpose, most of which require assembly and materials that are costly, reducing their usefulness in large-scale survey systems. This study tests an inexpensive and efficient trapping technique for detecting or surveying vespine wasps. Traps were made from reused plastic bottles containing a brown sugar and water bait. They were deployed at heights ranging from 0–6 m above ground in several configurations. Captures for traps suspended 1 m or greater above ground were, on average, nine times higher than the catch of ground-level traps. A rapid trap deployment method for large geographic areas was created, which captured seven different vespine wasp species along a 395 km east-west road transect from mountains to coastal plain in the Mid-Atlantic region of the United States. The trapping design and survey methodology described below is inexpensive and fast and could be used by land managers or citizen scientists to detect V. mandarinia, other exotic vespine, or conducted on a large-scale vespine diversity survey.

Baited trap, detection, Dolichovespula, exotic species, trap deployment, Vespula

Over the last several decades, there has been increased concern over the spread of exotic insect species due to international container shipping (Hulme 2009; Meurisse et al. 2019). Such species threaten native plant and insect communities both ecologically and economically. Vespid wasps are of particular concern because of the threat they pose to native pollinators. Until the appearance of Vespa mandarinia in the Pacific Northwest, there were no large-scale surveys for vespid species detection.

Fear over exotic wasp species introduction into North America spiked in 2019 with the arrival of the Giant Asian hornet. V. mandarinia is the largest bodied of any vespid (Hymenoptera, Vespidae) and is known for its ability to eradicate a bee colony in a matter of hours (Stankus 2020). Additionally, V. mandarinia can repeatedly deliver painful stings to humans which have caused extreme allergic reactions, resulting in 30–50 deaths per year in Japan (Stankus 2020). Models by Alaniz et al. (2020) predict damages between $12 and $102 million for bee-dependent products alone if V. mandarinia were to spread across the United States. Several established nests were found and eradicated in the Pacific Northwest, but other unverified sightings in the region have led many scientists and public officials to call for greater detection efforts (Stankus 2020; Animal and Plant Inspection Service 2021). There is a need for an inexpensive and reliable trap design that can be used for the coordinated detection of V. mandarinia over a large geographic range.

V. mandarinia has never been detected on the east coast of the United States, but other vespine species occupy the area and provide a proxy for testing V. mandarinia trapping methods. The most efficient way to detect vespine wasps related to V. mandarinia is through lethal trapping (Tripodi and Hardin 2020). Traps for vespine wasps often consist of a plastic bottle (usually a 1.5 L soda bottle or a gallon jug) filled with a liquid bait and hung from a tree branch (Dvorak 2007; Tripodi and Hardin 2020). Whether these traps are as effective when left on the ground is evaluated in this study.

Sugar-based foods are known to be effective bait for trapping some vespine species (Dvorak and Landolt 2006; Demichelis 2014; Tripodi and Hardin 2020). It is common for traps to contain a syrup or sugar mixture often with vinegar and fruit added, but a simple mix of dark brown sugar and water has proven effective if given enough time to ferment (Wegner and Jordan 2005; PDA 2020). Dark sugar bait was recommended by the Washington State Department of Agriculture in response to the first V. mandarinia detection (Tripodi and Hardin 2020).

In this study, a basic bottle trap with dark brown sugar bait was tested in the Mid-Atlantic region of the United States as an inexpensive and efficient method that could be used by seasonal technicians or citizen scientists to detect V. mandarinia or to survey other social wasp species that are attracted to fermented sugar baits. The bottle trap was tested at different heights, from ground level to 6 meters, and in different settings using a deployment method along roads in the region. Seven vespine species were detected from the genera Vespula, Dolichovespula, and Vespa.

Three experiments were run with identical bottle traps and sugar bait: 1) A hanging/ground experiment with paired and unpaired trials to compare the success of suspended and standing traps; 2) an elevated trap test that compared trap success at five heights from 0 to 6 m, and 3) a 395 km long transect, with traps deployed across multiple ecoregions.

Survey area

This study was conducted in the Mid-Atlantic portion of the United States, primarily in the state of Maryland. The first two experiments were conducted at the United States Geological Survey’s (USGS) Native Bee Inventory and Monitoring Lab (BIML) located on the United States Fish and Wildlife Service’s Patuxent Research Refuge (Laurel, Maryland, USA). Some traps were also placed in the surrounding community of Laurel, Maryland. The east-west road transect was performed on a route that started in Pennsylvania near the Maryland border (39°45'06"N, 79°23'29"W), traversed west to east, and ended in New Castle, Delaware near the Delaware River (39°39'35"N, 75°33'50W), staying between the latitudes of 39.5°N and 39.8°N (Fig. 1). The total route was approximately 395 km long and primarily used two-lane country roads that ran parallel to larger highways.

Figure 1. 

Trap locations and route of the east-west road transect. Trap locations (white dots) and route (black line) with state boundaries and level 3 ecoregions of the Environmental Protection Agency (Comeleo 2010).

The results of this study demonstrate that a 1–1.5 m hanging trap design, consisting of a re-used plastic bottle and a dark brown sugar bait mixture, is effective at trapping a diverse group of vespine wasps. Hanging traps performed, on average, nine times better than ground-based traps in overall catch across all experiments, and five times better in trap loss as shown by the east-west road transect, with an overall trap loss of only 5%. The elevated trap test demonstrated that ground-level placements perform significantly worse than all other heights, with traps 1.5 m and above performing similarly in their total catch.

The road transect captured seven of the ten vespine species recorded in the Maryland Biodiversity Project, a non-profit citizen science project that has cataloged over 11,000 insect species in Maryland (Maryland Biodiversity Project 2021). The vespine species captured includes all but one of the species listed with more than one confirmed sighting.

The biggest asset of this trap design and deployment technique is its accessibility and cost. Assuming bottles are freely collected from a recycling facility or receptacle, as these were, the only material expenses are for the dark brown sugar and string. For those materials, we estimate the per trap cost to be approximately $0.15. The only major expenses are gas and time. Approximately six traps spaced five km apart can be deployed or collected in an hour.

This trap design and a road transect deployment could be used to detect V. mandarinia and other exotic vespine species or as an inexpensive assessment of the component of regional vespine species that are attracted to fermenting sugar bait. This study demonstrated how many traps can be deployed inexpensively over a large geographic range. A small group of technicians could survey a large area using these traps and a methodology similar to the Breeding Bird Survey (Dunn et al. 2000). One example of this would be to divide the survey area into a grid of equal cell size or with cells oriented around physiographic strata. A point randomly generated within each cell and traced to the nearest road could be used as a starting point for a 25 km transect, with traps hung on the side of the road every kilometer. Two of these transects could be deployed or collected per day, meaning one technician could complete approximately 48 of these transects (1200 traps) in three months, given pick-up after three weeks and one day per week for sample transfer and storage into a freezer for later identification.

Additionally, the trap design would be ideal for a citizen science-based protocol for more large-scale surveys. Citizen science is growing in popularity as a method for surveying plants and wildlife, including exotic species. Pusceddu et al. (2019) used a verified citizen science program to monitor the spread of an invasive vespid species (Vespa crabro) on the island of Sardinia (Italy). The program reported high data accuracy and civil engagement.

Citizen science-based reporting could be a valuable tool for detecting and exterminating any Vespa mandarinia that find their way to North America. The US Department of Agriculture (USDA) called on scientists of the Pacific Northwest to assist with the detection of V. mandarinia after they first arrived in 2019 (Tripodi and Hardin 2020). The Washington Department of Agriculture has launched a 2021 Asian Giant Hornet Public Dashboard to continue these efforts using citizen scientist reporting (WSDA 2021).

The hanging trap and sugar-based bait tested in this study have shown to be effective at catching vespine wasps in high densities, and they would likely be effective as a passive, lethal trap for V. mandarinia. We recommend that this method of trapping be explored further as a widespread, citizen scientist approach for the detection of V. mandarinia. Unlike similar citizen science methodology, our trap design doesn’t require that land managers ship trap materials to participants (PDA 2020).

While inexpensive and accessible, these traps may not equally attract all vespine species (Dvorak 2007) and there could be high variance throughout the summer due to changes in dietary preferences (Stankus 2020; Tripodi and Hardin 2020). Similar traps have reportedly been used by Japanese farmers to capture and kill dispersing V. mandarinia queens in the spring and late fall (Tripodi and Hardin 2020), however future study is required to confirm the effectiveness of this trap design for V. mandarinia, and specifically for V. mandarinia queens if the design is to be used as a lethal capture to prevent species dispersal from year to year. Additionally, in any future study, we recommend that species and numbers of by-catch be recorded to assess the impact on non-target species.

The authors thank Sam Droege and the personnel of the USGS Native Bee Inventory and Monitoring Lab for instruction in entomology and valuable advice and feedback on this research. For employment and the opportunity to conduct this research, the authors thank the USGS Cooperative Summer Field Training Program and the USGS. Reviews by Jessica Reid, Hunter Martin, and Carol Barrera-Lopez (all USGS) are gratefully acknowledged. Gabrielle Jakobsberg and Charles Lott are thanked for their assistance in constructing Suppl. material.