Nesting Biology of the Solitary Wasp Pisoxylon amenkei (Hymenoptera, Crabronidae, Trypoxylini) in a Neotropical Hotspot of Southern Brazil.

Pisoxylon amenkei is a specie of solitary wasp that builds its nests in pre-existing cavities; it has only been recorded nesting in the Araucaria forest, one of the Atlantic forest phytophysiognomies and a biodiversity hotspot. So far, the only information on the biology of the genus Pisoxylon is based on one species. In addition, the genus has many similarities to Trypoxylon, showing an increased need for studies on the biology of these species of wasps. In the present study, we introduce unpublished information about Pisoxylon amenkei nesting biology and described many aspects of its natural history. Research was carried out between August 2017 and August 2019, in a rural area of Guarapuava municipality, Paraná, Brazil. Pisoxylon amenkei nested only in fragmented parts of Araucaria forest, during summer and autumn. It is a multivoltine species, and thus remains in diapause, in the pre-pupa phase during winter and spring. Their nests had an interior design similar to that of Pisoxylon xanthosoma and some Trypoxylon species, such as Trypoxylon lactitarse and Trypoxylon agamenon. Moreover, the sex ratio of P. amenkei was 1: 1, which can be linked to an equal cost in the production of females and males. Like other species of Pisoxylon, P. amenkei nests primarily in forest areas. In southern Brazil, it nests in fragments of Araucaria forest, which are threatened. Therefore, more efforts are needed to preserve these remaining fragments; a failure to do so could have devastating results, considering the number of threatened species that these forests house. We conclude that further studies should focus on the phylogeny of the group and use molecular analyses to clarify the hypothesis of Antropov (1998), that Pisoxylon should be classified as a subgenus of Trypoxylon.