A Wasp's Sweet Tooth: Foraging Responses to Honeydew in Two Sympatric Invasive Yellowjackets

ABSTRACT Carbohydrate‐rich resources can influence the foraging ecology of invasive social wasps and may affect their population dynamics, particularly in environments where floral resources are seasonal or unpredictable. Aphid honeydew may provide a temporally stable and abundant carbohydrate resource, but its use by invasive Vespula species remains poorly understood. In this study, we evaluated the sugar concentration of honeydew produced by giant willow aphid, Tuberolachnus salignus (Gmelin, 1790) (Hemiptera: Aphididae: Lachnini), and assessed its differential exploitation by two sympatric invasive yellowjackets, Vespula germanica (Fabricius, 1775) and Vespula vulgaris (Linnaeus, 1758) (Hymenoptera: Vespidae: Vespini), which co‐occur in northern Patagonia and forage on this resource. The aims of our study were to (i) describe and compare the seasonal population dynamics of V. germanica and V. vulgaris , (ii) determine the nutritional value (sugar concentration) of the honeydew and (iii) evaluate whether these species have distinct foraging patterns in the field. Wasp phenological data revealed that both wasp species followed unimodal seasonal activity curves but slightly differed in the timing and magnitude of their population peaks, with V. vulgaris peaking approximately 5 days later than V. germanica and nearly 50% higher cumulative seasonal activity. Honeydew averaged 15.1 °Brix and showed seasonal variation, decreasing over time while increasing with branch height. Vespula germanica and V. vulgaris showed overlapping seasonal activity under willows, although V. vulgaris showed weakly higher foraging levels than V. germanica. Both species exploited fresh T. salignus honeydew; however, V. germanica responded more strongly to higher sugar concentration, whereas V. vulgaris also exploited honeydew with lower sugar concentrations. These foraging patterns suggest that species‐specific differences in gustatory sensitivity could drive differential foraging responses to fresh T. salignus honeydew quality, with potential implications for resource use and population dynamics of these co‐occurring invasive wasps in temperate Patagonian habitats.