Does the distance among nest clusters affects reproductive success in Ammophila sabulosa (Hymenoptera, Sphecidae)?

A population of Ammophila sabulosa (Linnaeus 1758) in the Upper Valtellina (Northern Italy) was observed during in 1996. The 20 females object of this study dug a total of 120 nests. Each A. sabulosa nest was opened after the provisioning and at the end of the season, to check the status of prey, A. sabulosa larvae and pupae and the loss of brood due to biological factors. We found that 69.2% of the 120 nests were provisioned, but the larvae pupated in only 29.1% of provisioned nests. Brood loss was due to parasitism by Diptera Sarcophagidae and Hymenoptera Ichneumonidae (3.6% of provisioned nests), to cleptoparasitism by conspecific females (14.4% of provisioned nests) and to mites and nematodes (49.3% of provisioned nests). Using a new approach in entomology research, the nest clusters of different females were compared by means of distance weighted centroids, to evaluate the influence of nest cluster distances on reproductive success. Based on our observations, intraspecific parasitism is a common phenomenon among adjacent nests clusters: the distances among nest clusters of the females whose nests were parasitized by conspecifics are significant lower than the distances among nest clusters of females whose nest were not parasitized by conspecifics. Interestingly, intraspecific parasitism was. not affected by nest densities, defined as the number of nests within the nest cluster. In conclusion, we believe that the novel technique of nests examination we introduced, provides a valid tool for studying nesting behaviour in wasps with shallow ground nests like A. sabulosa.