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Winter in climatic regions with low temperatures is a challenge for overwintering insects. They are exposed to temperature extremes, which directly cause mortality or lead to energy depletion. The winter hibernaculum of paper wasp gynes protects from predators and rain, but only poorly from ambient temperature. In order to detect physiological adaptations to differing climates, we compared the respiratory metabolism of overwintering gynes of two polistine species from the Mediterranean climate in Italy (Polistes dominula and Polistes gallicus), and of one species from the temperate climate in Austria (Polistes dominula). The wasps' CO2 emission was measured with stop‐flow respirometry in a temperature range from 2.5 to 20 °C. The mass‐specific standard (resting) metabolic rate, the main type of metabolism of the dormant insects during overwintering, increased exponentially with ambient temperature but was suppressed in comparison to individuals measured in the summer, which conserves the energy stores. In addition, it was lower in the Mediterranean species (P. dominula and P. gallicus) in comparison to the temperate species (P. dominula), especially at higher temperatures. The active metabolic rate was suppressed to a similar amount. The suppressed metabolism of the overwintering Mediterranean gynes could be an adaptation to the higher winter temperatures to prevent a premature depletion of the energy resources. [ABSTRACT FROM AUTHOR]

The pupal parasitoid Pimpla turionellae (L.) uses self-produced vibrations transmitted on the plant substrate, so-called vibrational sounding, to locate immobile concealed pupal hosts. The wasps are able to use vibrational sounding reliably over a broad range of ambient temperatures and even show an increased signal frequency and intensity at low temperatures. The present study investigates how control of body temperature in the wasps by endothermic mechanisms may facilitate host location under changing thermal environments. Insect body temperature is measured with real-time IR thermography on plant-stem models at temperature treatments of 10, 18, 26 and 30 °C, whereas behaviour is recorded with respect to vibrational host location. The results reveal a low-level endothermy that likely interferes with vibrational sound production because it occurs only in nonsearching females. At the lowest temperature of 10 °C, the thoracic temperature is 1.15 °C warmer than the ambient surface temperature whereas, at the high temperatures of 26 and 30 ° C, the wasps cool down their thorax by 0.29 and 0.47 °C, respectively, and their head by 0.45 and 0.61 °C below ambient surface temperature. By contrast, regardless of ambient temperature, searching females always have a slightly elevated body temperature of at most 0.30 °C above the ambient surface temperature. Behavioural observations indicate that searching females interrupt host location more frequently at suboptimal temperatures, presumably due to the requirements of thermoregulation. It is assumed that both mechanisms, producing vibrations for host location and low-level endothermy, are located in the thorax. Endothermy by thoracic muscle work probably disturbs signal structure of vibrational sounding, so the processes cannot be used at the same time. [ABSTRACT FROM AUTHOR]