Is the social wasp Polybia paulista a silent victim of neonicotinoid contamination?

Neonicotinoids are among the chemicals most widely used against insects considered agricultural pests, although they may also affect nontarget species, as has been reported for social bees. Social wasps are recognized as efficient predators of larvae of other insects, including pest species, so they may have contact with insecticides, at least indirectly. However, to date, there have been no studies investigating the consequences for social wasps of the use of neonicotinoids. Therefore, the aim of this study was to obtain the topical and oral acute lethal mean doses of the neonicotinoid thiamethoxam, as well as to evaluate the effects of sublethal contamination, for the social wasp Polybia paulista. Foraging wasps were exposed orally and topically, with monitoring of their mortality after 24 and 48 h, in order to calculate the LD50 values. Other wasps were then exposed with sublethal doses, in order to evaluate the effects of contamination on their mobility. The results indicated that P. paulista workers are as sensitive to thiamethoxam contamination as several nontarget species studied previously. Exposure to a sublethal dose (LD10) negatively affected their mobility. It could be concluded that social wasp colonies may be as much affected by exposure to neonicotinoids as social bees. Further toxicological studies should be conducted, evaluating other parameters and different species, in order to understand the extent of the problems faced by these insects due to the use of neonicotinoids.

A 3D model to illustrate the nest architecture of Acromyrmex balzani (Hymenoptera; Formicidae)

ABSTRACT For eusocial insects, the nest is a place where the main social interactions occur. The nest architecture ensures protection from predators and the environment, as well as suitable conditions for brood rearing, food storage, and in some cases the cultivation of fungus farms. Variations in nest architecture can occur, according to the environmental conditions. In order to elucidate the internal organization of nests, most studies use 2D schemes and photographs to illustrate the nest architecture models. However, 3D models can provide a different and more realistic view of the nest architecture. The aim of this study was to describe the nest architecture and colony size of the grass-cutting ant Acromyrmex balzani (Emery), using 3D models to illustrate these features. The structures of eight colonies were measured and the data were used to create a 3D model of each nest. Externally, the nests had one or more piles of loose soil and waste, with a single straw turret over the entrance. Underground, the nests had from 2 to 6 chambers, at a maximum depth of 122 cm. It could be concluded that the observed nest architecture of Acromyrmex balzani followed, at least in part, the pattern already reported in the literature. However, this is the first report of connection between two chambers made by two shafts, as well as the presence of the turret at the nest entrance/exit, regardless of the season of the year. These differences evidence that the nest structures may vary, depending on intrinsic or local environmental conditions.