Are invasive species promoting yellowjacket invasion in Patagonia?

Abstract

In recent decades, yellowjacket wasps, including Vespula vulgaris, have successfully been established in Patagonia. Additionally, the invasive willow Salix fragilis has also invaded areas next to watercourses, which in turn are typically colonized by the giant willow aphid (GWA, Tuberolagnus salignus), another invasive species. The honeydew exuded by the aphids has been reported to be used as a carbohydrate source by this social wasp. Our aim was to determine whether willows and GWA (invasive complex) on the stream shores promotes yellowjacket population growth. We worked under the hypothesis that GWA provides honeydew (i.e. carbohydrates) to yellowjackets, favouring nest growth and individual fitness. Our results indicate that habitats close (<200 m) to stream margins, where S. fragilis and GWA occur, contain not only a greater abundance of workers but also a higher nest density of V. vulgaris yellowjackets. Even though the nests were similar in size irrespective of the distance to the stream, weight, size and nutritional status of individuals suggest that foraging/nesting in proximity of the invasive complex promotes larger and better nurtured wasps, including reproductive castes, that in the long run could drive population growth and spread of the species in Patagonia. In this context, our study suggests that management of V. vulgaris populations should adopt strategies that encompass a broad approach, especially adopting new strategies designed to contemplate relevant multitrophic interactions between yellowjackets and invasive willows and aphids.

Honeydew production by the giant willow aphid (Tuberolachnus salignus, Hemiptera: Aphididae) and its effect on foraging yellowjackets (Hymenoptera: Vespidae)

“…Nevertheless, factors such as the coinciding seasonality, the high volumes produced and predictability of its location/ease of access could translate into an important driver for vespid colony success. The effect was suggested in a recent study conducted in the area looking at V. vulgaris nest size and distribution, and found that habitats close (< 200 m) to stream margins, where Salix fragilis and GWA occur, contain higher nest densities with larger individuals 23 . It is important to note that our sampling protocol did not distinguish between the two yellowjacket species present in Patagonia, since identification is difficult to be carried out on non‐stationary individuals.…”

“…forests are not infested with hemipterans and wasps do not reach the high densities observed in New Zealand 28 . However, a recent study suggested that yellowjackets may be favored by GWA as V. vulgaris nest size and density in habitats close (< 200 m) to stream margins, where Salix fragilis and GWA occur, are higher and produce larger individuals than in sites without willows and aphid 23 . It is important to note that GWA and Vespula spp.…”

“…Many hymenopteran species take advantage of aphid exudate as a resource in regions where GWA and Salix fragilis coexist, 22–24 including honeybees, bumblebees and yellowjackets. The food (proteins and carbohydrates) consumed by Vespula spp.…”

“…19 Also the exudate depositions can affect soil biota 20,21 and impact apiculture; honey bees that feed on the exudate produce lower quality honey due to its high content of the trisaccharide melezitose. 17,22 Many hymenopteran species take advantage of aphid exudate as a resource in regions where GWA and Salix fragilis coexist, [22][23][24] including honeybees, bumblebees and yellowjackets. The food (proteins and carbohydrates) consumed by Vespula spp.…”

“…28 However, a recent study suggested that yellowjackets may be favored by GWA as V. vulgaris nest size and density in habitats close (< 200 m) to stream margins, where Salix fragilis and GWA occur, are higher and produce larger individuals than in sites without willows and aphid. 23 It is important to note that GWA and Vespula spp. have coevolved, therefore wasps could be innately attracted to their honeydew.…”