DOI: 10.5061/dryad.k98sf7mh6
title: Data from: Non-native Vespula germanica yellowjackets dominate urban-to-rural gradient

description: Social insects are highly successful invaders of novel habitats and, of
 these, wasps and yellowjackets are quite successful worldwide. Vespula
 germanica (German yellowjackets) have become a pernicious cosmopolitan
 problem – yet the degree of their urban association and domination remains
 unclear. We investigated the invasion and behavior of V. germanica in
 Western New York along a rural-urban gradient to understand their
 conspecific dominance and their foraging behavior around human activities.
 We placed yellowjacket baits in urban, suburban and rural sites through
 the summer season to assess their dominance, and we conducted behavior
 trials at picnic tables to observe their responses to human activity.
 Given that the invasive ecotype prefers to nest in human structures, we
 predicted we would find the greater V. germanica dominance near structures
 and in urban areas. Moreover, given that they learn to associate food with
 cues, we predicted that they would associate human presence/activity at
 picnic tables with food. We found that V. germanica dominated everywhere
 (70-95% of all Vespula wasps), but dominance was highest in suburban and
 urban areas, with a preference for foraging near human structures.
 Surprisingly, behavior trials revealed that the yellowjackets were less
 attracted to baits with humans nearby, suggesting an avoidance of human
 activity rather than learned affinity. These findings reinforce V.
 germanica's attraction to human structures and urban environments,
 and their high negative impact on native yellowjacket populations.
description: The study area fell within the Western New York (U.S.) geographic
 area, bounded on the northern and eastern edges by Lakes Ontario and Erie,
 the western edge by Rochester, NY and the southern edge by the Alleghany
 Plateau. The study area included urban (the greater metropolitan areas of
 Buffalo, Niagara Falls, and Rochester) suburban and rural habitats and
 encompassed about 12,000 km<sup>2</sup>. Within that area, we
 acquired permission from municipal and private entities, and from that
 pool randomly we selected sites that were urban (dominated by impermeable
 surfaces; no single-family housing), suburban (permeable surfaces such as
 lawns and trees; dominated by single-family housing) and rural (dominated
 by permeable surfaces such as agricultural fields and forests; sporadic
 single-family housing). Every two weeks for 20 weeks (June-November 2022)
 we sampled 9 sites (3 of each: urban, suburban and rural). We captured no
 insects during the first baiting (June 13), so we resampled the same sites
 for the second baiting (June 27), resulting in <em>n</em> = 99
 baiting events at 90 unique sites (<em>n</em> = 30 site in
 each land use category). Given that the urban-rural ‘gradient’ can be
 considered more conceptual than empirical with boundaries that can be hard
 to identify (Wandl et al. 2014; Warren et al. 2018), we treated land use
 as categorical (urban, suburban and rural) and selected different sites
 from within each category for each sampling. We also chose this approach
 because destructively sampling workers at the same location through the
 summer might confound results with time. By using land use as a treatment,
 however, we retained the ability to quantify seasonal effects. The minimum
 distance between sites was 1.5 km; the maximum was 115 km.
 At each baiting location each week, we placed a Victor
 yellowjacket trap filled with 60% Italian water ice concentrate (diluted
 1:1 with water) and 40% beer (Goldstein 1996). We chose the Victor traps
 because we were sampling in urban and suburban areas, and the commercial
 traps are recognizable to the public. The sugar and yeast attract the
 <em>Vespula</em> yellowjackets, and the alcohol kills them.
 Whereas other methods of trapping <em>Vespula</em>
 yellowjackets may be more effective overall (Landolt 1998; Haupt et al.
 2019), given that we were leaving traps in public areas, and we were
 measuring relative and not absolute abundance, we chose this approach
 because it has been demonstrated effective in an urban setting (Goldstein
 1996) and to minimize non-target animal interference and toxicity. We used
 a trap and bait (sugar and alcohol) combination normally used to manage
 <em>Vespula</em> populations that is not attractive to
 nontarget insects, including other wasps and bees, but there is little
 data comparing bait preferences amongst <em>Vespula</em>
 species – though there is some indication that <em>V.
 germanica</em> workers prefer protein baits more than some other
 <em>Vespula</em> species (Harris 1991; Harris and Oliver 1993;
 Pereira et al. 2013). Generally, the traps were placed on hard surfaces,
 like picnic tables, road curbs and porch steps. The traps were left out
 from morning to dusk, ~8 hours. We avoided placing traps during inclement
 weather, which sometimes lasted for several days.
 During preliminary research, we noticed
 that <em>Vespula</em> yellowjackets swarmed around people
 eating outdoors, and a preliminary class project suggested that they were
 more likely to visit baits with students standing nearby than those left
 alone. Given that the preliminary project was conducted in September, we
 suspected that, if this behavior was present, it might be learned from
 previous summer foraging. Hence, we sought to test whether yellowjackets
 on campus learn to associate food with people eating outside at picnic
 tables. We randomly chose four separate picnic tables (from 17 potential
 picnic tables; all at least 100 m apart) on the SUNY Buffalo State
 University campus and placed a Victor trap on each for one hour once a
 week for nine weeks between August and October 2022. Because we were
 investigating the association between human activity and food, and not
 human food, we used the same baiting formula as the gradient study given
 that it would not be as familiar to the campus foraging
 <em>Vespula</em> yellowjackets. For one hour at ‘lunchtime’
 (12-1 pm), a single person sat at two of the four picnic tables 0.5 m from
 the Victor trap (the other two tables were left alone as controls). The
 humans made moderate movements as if they were eating during the trial
 periods. All collected wasps were identified to species
 using Akre (1981), Buck (2008), Kimsey and Carpenter (2012). Voucher
 specimens are stored at Buffalo State University.
description: # Data from: Non-native Vespula germanica yellowjackets dominate
 urban-to-rural gradient \#Gradient data Date = date traps placed Julian =
 Julian date traps placed Lat = Latitude Lon = Longitude Dist.home =
 distance from the trap to the nearest human structure Land.use = land use
 category for location where trap placed (Rural, Suburban, Urban)
 V.germanica, V. maculifera, V.flavipolus = Abundance of each Vespula
 species in trap D.arenaria = abundance of Dolichovespula arenaria in trap
 \#Behavior data Date = date traps placed Julian = Julian date traps placed
 Week = treatment week Replicate = nearest campus building Table = table
 where trap placed Treatment = Control or Observed V.germanica = abundance
 of V. germanica Other = other wasps in traps NA = missing data