Nesting Biology, Sexual Dimorphism, And Populational Morphometric Variation In Podium Denticulatum F. Smith, 1856 (Hymenoptera: Sphecidae)

Podium denticulatum occurs from Mexico to southern Brazil, including northeastern Argentina. Females use pre-existing cavities to build nests, consisting of cells separated by walls of mud and resin and massively provisioned with paralyzed cockroaches. Trap-nests were disposed in three localities in the state of Sao Paulo, Brazil (Araras, Sao Carlos, Rifaina), resulting in the sampling of 201 nests from December/2003 to June/2007. The founding nests were brought to the laboratory, opened and the pupae transferred to identified vials until the emergence of the adults, when they were then weighed, sexed and stored at -20 degrees C. The nesting activity was highly seasonal, since almost all nests were collected in the warm and rainy period of the year. The number of constructed cells ranged from one to nine per nest. The emergence rate of adults in the 716 brood cells was 74%, with mortality homogeneously distributed by egg, larva and pupa stages. This mortality was partly due to parasitism observed in 39% of nests, predominantly by Melittobia sp. A 1:1 sex ratio was observed among the newly emerged adults of each area analyzed. Strong sexual dimorphism was characterized by linear measurements of wings and body mass, with females and males showing a mass between 27-116 mg and 14-70 mg, respectively. The geometric morphometry confirmed this dimorphism and revealed significant variation of wing size and shape among individuals of the analyzed populations, a result that deserves subsequent studies to point out the factors that account for this differentiation.