Abstract
Trypoxylon (Trypargilum) (Crabronidae) wasps are solitary spider predators that can build their nests in artificial trap-nests, which enables study of their nesting architecture and biology. Twenty traps (each containing 15-30 internodes of cane) were placed in each of nine sites of Chaco Serrano Woodland in Central Argentina (Córdoba) in October 2005, and were recovered in June 2006. We obtained 91 nests of four species of Trypoxylon (Trypargilum). In the laboratory, each Trypoxylon nest was sectioned longitudinally to study its architecture. The number of brood cells was counted, and the occurrence and length of vestibular and intercalary cells and the pre-closing plug space were recorded. We measured the diameter of the cane entrance, total length of the nest, length of each brood cell, maximum thickness of mud partitions and closing plug thickness. We also recorded the cell contents: the wasps, their natural enemies and the prey spiders. Mortality was assessed and the sex ratio calculated for each species. Finally, the nests were examined to help clarify the function of the vestibular cell. The nest architecture was similar in the four species, with linear brood cells located one after the other separated by mud partitions, as in other species of the subgenus Trypargilum. Forty-eight percent of the nests had vestibular cells, but only two had intercalary cells. The thickness of the mud partitions and the length of the brood cells differed among species and were related to the size of the emerged wasp. The diameter of the nest entrance was directly related to the average length of the fore-tibia. Sex ratios of all species did not deviate from 0.5. Mortality due to parasitoids (Eulophidae; Melittobia sp.) was similar among species, while the mortality due to cuckoo wasps (Chrysididae) in T. lactitarse was higher than in the other species. The presence of vestibular cells was not related either to the mortality due to natural enemies or to the orientation of the trap in the field. Spiders in the family Araneidae were the most frequently collected prey.
Highlights
Crabronidae wasps are cosmopolitan solitary predators which use insects and spiders as provisions for their nests
The aim of this study was to present comparative information about the nesting biology of four species of Trypoxylon (Trypargilum), using trap-nests in Chaco Serrano woodland in Córdoba, Argentina and to analyze Trypoxylon nests to help clarify the function of the outermost empty chamber of the nest, the vestibular cell (VC)
Sixteen percent of all nests presented a preliminary plug, 48% a VC and 60% a pre-closing plug space (PCPS), whereas intercalary cells occurred in just two nests of T. aff. nitidum aztecum (Fig. 3)
Summary
Crabronidae wasps are cosmopolitan solitary predators which use insects and spiders as provisions for their nests. The species of the subgenus Trypargilum Richards, 1934 are restricted to the New World (Bohart & Menke 1976, Coville 1982) Some species of this subgenus constructs mud nests; others utilize pre-existing tubular cavities that are divided into a linear series of cells by mud partitions. The cavity adopted by the wasp may be a tube in the hollowed pith of a twig, an old insect borehole in rotten wood, or many other kinds of holes This opportunistic nesting habit allows researchers to use trap-nests in order to study many aspects of the biology of these wasps (Krombein 1967). The aim of this study was to present comparative information about the nesting biology of four species of Trypoxylon (Trypargilum), using trap-nests in Chaco Serrano woodland in Córdoba, Argentina and to analyze Trypoxylon nests to help clarify the function of the outermost empty chamber of the nest, the vestibular cell (VC)
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