Gustatory responsiveness in Vespula germanica workers: exploring the interplay between sensory perception and task specialization.

Workers' task specialization and division of labor are critical features of social insects' ecological success. It has been proposed that the division of labor relies on response threshold models: individuals varying their sensitivity (and responsiveness) to biologically relevant stimuli and performing a specific task when a stimulus exceeds an internal threshold. In this work, we study carbohydrate and protein responsiveness and their relation to worker task specialization in Vespula germanica, an invasive social wasp. The sucrose and peptone responsiveness of two different subcastes, preforagers and foragers, was determined by stimulating the antenna of the wasps with increasing concentrations of the solution and quantifying whether each concentration elicited a licking response. We studied responsiveness in five different ways: (1) response threshold, (2) concentration 50 (concentration to which at least 50% of wasps responded), (3) maximum response, (4) mean scores and (5) median scores. Our results suggest that V. germanica foragers are more sensitive to sucrose (lower thresholds) than preforager workers. However, we found no differences for peptone thresholds (i.e., a protein resource). Nonetheless, this is the first study to investigate response thresholds for protein resources. The intercaste variation in sucrose responsiveness shown in our work contributes to the existing knowledge about response threshold theory as a mechanism for task specialization observed in V. germanica.

Sugar responsiveness could determine foraging patterns in yellowjackets.

Sympatric-related species often exhibit resource partitioning. This can occur through different mechanisms, such as behavioral, morphological, and sensory variations, leading to qualitative, temporal, or spatial differences in resource exploitation, such as consuming different types of food. Sensory-based niche partitioning could be the underlying mechanism through which closely related species effectively reduce niche overlap. Here we ask whether variations in sensory responses to carbohydrates could reflect differences in the foraging patterns of two Vespula species present in Patagonia. For this, we established (i) the response thresholds toward carbohydrate solutions of foraging V. germanica and V. vulgaris in the laboratory, (ii) the sugar concentration of foraged carbohydrates in the field, and (iii) possible effects of incoming sugar concentration and performance at individual and colony levels. Results indicate a higher sucrose response threshold in V. germanica than V. vulgaris. Field results indicate that higher carbohydrate concentrations foraged by V. germanica, with 57% of V. germanica foragers returning with concentrations above 50% w/w, while only 23% of V. vulgaris foragers did so. These differences in sucrose sensitivity and foraging patterns positively correlate with colony size, irrespective of the species. Our results suggest that competition could be reduced in these closely related invasive social wasp species through sensory differences in their sugar perception levels, which would lead to them foraging different carbohydrate sources. This study suggests that sensory niche partitioning could promote species coexistence in these social wasps.

Flexible foraging decisions made by workers of the social wasp Vespula germanica (Hymenoptera: Vespidae) in response to different resources: influence of ontogenetic shifts and colony feedback.

Decisions made by foraging animals conform a complex process based on the integration of information from multiple external environmental stimuli and internal physiological signals, which in turn are modulated by individual experience and a detection threshold of each individual. For social insects in which foraging is limited to given age subcastes, individual foraging decisions may also be affected by ontogenetic shifts and colony requirements. We studied the short-term changes in foraging preferences of the generalist wasp Vespula germanica, focusing on whether the individual response to different resources could be influenced by the ontogenetic shifts and/or by social interaction with nestmates. We carried both laboratory and field experiments to confront worker wasps to a short-term resource switch between either protein or carbohydrate-based foods. We tested the response of (1) Preforager workers (no foraging experience nor interaction with other wasps), (2) Forager workers (experience in foraging and no colony feedback), and (3) Wild forager workers (foraging naturally and exposed to free interactions with nestmates). We evaluated the maxilla-labium extension response (MaLER) for laboratory assays or the landing response for field assays. We observed that for wasps deprived of colony feedback (either preforagers or foragers), the protein-rich foods acceptance threshold increased (and thus a lower level of foraging on that item was observed) if they had foraged on carbohydrates previously, whereas carbohydrates were accepted in all assays. However, wasps immersed in a natural foraging context did accept protein foods regardless of their first foraging experience and reduced the carbohydrates collected when trained on protein foods. We provide evidence that short-term changes in foraging preferences depend on the type of resource foraged and on the social interactions, but not on ontogenetic shifts.

Brewer's Yeast, Saccharomyces cerevisiae, Enhances Attraction of Two Invasive Yellowjackets (Hymenoptera: Vespidae) to Dried Fruit and Fruit Powder.

The German yellowjacket, Vespula germanica F., and common yellowjacket, Vespula vulgaris L. (Hymenoptera: Vespidae), are pests of significant economic, environmental, and medical importance in many countries. There is a need for the development and improvement of attractive baits that can be deployed in traps to capture and kill these wasps in areas where they are a problem. Yellowjackets are known to feed on fermenting fruit, but this resource is seldom considered as a bait due to its ephemeral nature and its potential attractiveness to nontarget species. We analyzed the headspace volatiles of dried fruit and fruit powder baits with and without Brewer's yeast, Saccharomyces cerevisiae, using gas chromatography-mass spectrometry, and we field tested these baits for their attractiveness to yellowjackets in Argentina. The addition of yeast to dried fruit and fruit powder changed the volatile compositions, increasing the number of alcohols and acids and decreasing the number of aldehydes. Dried fruit and fruit powder baits on their own were hardly attractive to yellowjackets, but the addition of yeast improved their attractiveness by 9- to 50-fold and surpassed the attractiveness of a commercial heptyl butyrate-based wasp lure. We suggest that further research be done to test additional varieties and species of yeasts. A dried fruit or fruit powder bait in combination with yeast could become a useful tool in the management of yellowjackets.