Nest thermoregulation in Polybia scutellaris (White) (Hymenoptera: Vespidae)

Abstract

-Polybia scutellaris (White) builds large nests characterized by numerous spiny projections on the surface. In order to determine whether or not the nest temperature is maintained because of homeothermic conditions of the nest individuals or otherwise, we investigated the thermal conditions within the nests built by P. scutellaris. We measured the temperature within active and abandoned nests. The temperature in the active nest was almost stable at 27°C during data collection, whereas the temperature in the abandoned nest varied with changes in ambient temperature. These results suggest that nest temperature was maintained by the thermogenesis of the individuals of the colony. This is the first report of nest incubation caused by thermogenesis of species of Polybia wasps.KEY WORDS: Epiponini, nest architecture, nest temperature It is well established that social wasps regulate the internal temperature of their nests (Heinrich 1993). Many vespid species from cold to tropical regions maintain a constant nest temperature (28-30°C) during production of the first sexuals (Martin 1990). However, few studies have dealt with the thermal conditions of nests built by epiponine wasps, which predominantly inhabit the neotropical and neosubtropical ecozones. Hozumi et al (2005Hozumi et al ( , 2008 revealed that unlike in the case of the vespine nests, the temperature in Polybia nests were strongly related to both the nest architecture and the microenvironment of the nesting sites, and that this species generates little heat for nest incubation. Polybia scutellaris (White) is a consubgeneric species of P. occidenalis Oliver, which forms large colonies and builds nests characterized with many spiny projections on the surface (Richards 1978). However, details of the nest architecture with regard to the internal thermal conditions and the thermal conditions of the microenvironment have not yet been studied. In here, the architecture of P. scutellaris nests was studied and nest temperatures were measured during this short study.Three abandoned nests were collected from Cajuru (21°16′S, 47°17′W), São Paulo State, Brazil. The thickness of the nest envelope and the size of the spines were measured to the nearest 0.1 cm with vernier calipers. The thickness of the envelope was measured around the entrance of the nest and at the sides. Twenty spines were randomly chosen from each nest, and the maximum height and width of the spines were measured.The temperature of an active P. scutellaris nest found on the west-facing concrete wall of a building in Cajuru was measured (Fig 1a). The nest was built 2.5 m above the ground and was located just below the eaves (Fig 1c). Polybia scutellaris carries out nesting activities even during the winter season, and in mid-July, the nest was found to contain >30,000 adults. The nest was composed of plant materials and oral secretions, which function as a binding agent and a water repellent. The nest was approximately 34 × 40 × 35 cm (L × W × H) in size and had >800 spines on the surface. The i...

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