Nicole Höcherl

In North America,Polistes dominulacauses a stir because it spreads very fast in this region upon its recent introduction. Many different explanations are presented in the literature whyP. dominulais such a good invader. In Europe, the invasion of this species into northern regions is also on the rise. Since little is known about the nesting behavior ofP. dominulain Central Europe, we investigated basic principles about nesting in Germany (latitude 49°). We found out that foundress groups (one to four foundresses) and nests are smaller and that the nesting season is shorter than in other regions. The mean size of newly founded nests was 83 cells and we recorded an average length of nesting season of 4.6 months. The queens neither preferred single (54%) nor multiple founding (46%). The major benefit of multiple founding is an increased rate of survival. Only 47% of single‐foundress colonies survived, whereas 100% of colonies that were built by more than two queens, survived. However, there was no impact of the number of foundresses on the productivity of colonies in terms of number of cells and pupae per nest. Furthermore, we observed that the length of the nesting season as well as the nest sizes varied greatly in three consecutive years depending on the climatic conditions of the preceding winter. These results imply thatP. dominulais remarkably flexible and reacts very quickly to outside conditions. This adaptation could be one explanation for the rapid spread of this species into colder areas.

Paper wasps, like Polistes dominula, are considered as primitively eusocial. Hence, they are often used as model species for studies about the evolution of eusociality and dominance hierarchies. However, our knowledge about basic physiological processes in these wasps remains limited. In particular, the thermoregulation of individual wasps in their natural habitat has not yet been investigated in detail. We conducted a comprehensive field study to test their ability to respond to external hazards with elevated thorax temperatures. We presented artificial threats by applying smoke or carbon dioxide simulating fire and predator attacks, respectively, and monitored the thorax temperature of wasps on the nest using infrared thermography. We found that P. dominula workers recognized smoke and CO₂ and reacted almost instantaneously and simultaneously with an increase of their thorax temperature. The maximal thorax temperature was reached about 65 s after the application of both stressors, but subsequently, the wasps showed a different behaviour pattern. No rise of the thorax temperature was detectable after an air blast was applied or in wasps resting on the nest. These observations provide evidence that P. dominula is able to heat up its thorax and that thermoregulation is employed in escape and defence reactions. Additionally, we investigated the thorax temperatures of queens during dominance battles. We found that the thorax temperature of the dominant queens rose up to 5 °C compared to that of subordinate queens that attacked the former, suggesting that the dominant queen defends herself as well as her nest.