The interplay between social wasps and fruit crops can be a difficult relationship for growers to navigate. On one hand, wasps can be major vineyard pests, as they represent a stinging threat for visitors and workers, and may even damage grapes to feed upon their sugars. However, wasps are also beneficial, as they provide some pollination services and are predatory insects that help regulate other pestiferous vineyard species. Furthermore, not all social wasp species represent the same level of threat to vineyards, complicating the ability to find a healthy balance between the beneficial and pest aspects of this group of insects.

In a previous study, we looked at the seasonal pattern and species composition of social wasps in Wisconsin vineyards and identified two common social wasp genera in Southwest Wisconsin Vineyards, Vespula and Polistes. Vespula, known commonly as a yellow jackets or hornets, are shiny, bare of hair, and sleeker than bees. Polistes, also called paper wasps, may look similar to Vespula, but have slightly darker, more elongated bodies, and long legs that dangle in flight (Fig, 2). Both are prevalent near wooded locations, since they utilize a mix of saliva and wood to build complex paper nests. These nests can be found in sheltered locations, such as the eaves of houses, or in underground areas, which pose an increased risk to workers who may come across them unexpectedly. In addition, Vespula and Polistes are often confused, one for another or with other species, due to similar black and yellow markings.

In our study, we found that populations of Vespula greatly outnumbered Polistes, and represent the largest threat to growers. This was especially true in August as grapes began to ripen and Vespula populations quickly ramped up at most vineyards. Polistes maintained a constant presence throughout the growing season, but at much lower population levels, and seems to represent little to no risk to grapes, at least in 2015 (Fig.1). This large split between abundances may be due to the ability for Vespula species’ to learn quickly from olfactory cues, which allows them to return easily to a food source once successful. Furthermore, Vespula are scavengers, which consume a larger variety of non-living foods such as carrion, garbage, and other human produce. Whereas studies indicate Polistes prefer caterpillars to feed their larvae, both genera are opportunists that feed on a range of arthropods like beetle grubs, grasshoppers, flies, aphids, spiders, and available sources of carbohydrates like nectars and honeydew.

Our previous study identified four predominant species of social wasps in Wisconsin vineyards in 2015 (Vespula maculifrons, Vespula germanica, Vespula vidua, and Vespula Floabopilosa). Of these, we do not know yet which are more likely to be pests of grapes and whether they can do the actual damage to intact common table and wine cold climate grapes. We received funding from DATCP to assess these questions this summer. We are also interested in determining if the patterns we observed in 2015 are consistent. Social wasps often locate food sources by responding to volatiles released by plants when their tissues are under attack from herbivorous insects. Therefore, our current study will seek to utilize chemicals that mimic these volatiles and other natural food sources, to identify optimal attractants as well as repellents to create a push-pull strategy that helps manage Vespula as a vineyard pest going into the future.

Currently, methods for managing wasps are limited and were discussed in a volume 1, issue 8 of this newsletter. So far this season, populations have been incredibly low and the total number of wasps per week in our vineyard traps have stayed below five, with the exception of one week in which we caught 37. Wasp populations could potentially remain low this year, possibly due to the high moisture, or simply rise later than in previous seasons. We will keep you posted as the season progresses.