ECOLOGY OF CRABRONID WASPS FOUND IN TRAP NESTS FROM SPAIN (HYMENOPTERA: SPHECIFORMES)

Abstract

We report data obtained concerning the occupation of trap nests by xylicolous Crabronidae (sensu Melo 1999) in a study carried out in central Spain between 1992 and 1995. In particular, we analyze the data on the occupation of the nests for Psenulus concolor (Dahlbom), Trypoxylon attenuatum F. Smith, and Trypoxylon beaumonti Antropov. All three species use pre-existing cavities of 2-4 mm to establish their nests. The mortality rates varied between 33% and 55%, and of special interest was the variation between the two species of Trypoxylon L. and the absence of mortality due to natural enemies in P. concolor. In the three species, mortality was similar along the nests, with no increase in the innermost or outermost cells. Trichrysis cyanea (L.) was the most abundant natural enemy in the nests analyzed. Sex distribution was not random in any of the species studied: in P. concolor and T. attenuatum, the males developed in the outermost cells, while in T. beaumonti they appeared in the innermost ones. The sex ratio did not deviate from 0.5 in P. concolor and T. attenuaum, although in T. beaumonti, the number of females was significantly higher than that of males.