Sex-specific patterns of individual growth, resulting in sexual size dimorphism (SSD), are a little studied aspect of the ontogeny related to the evolutionary history and affected by the ecology of a species. We used empirical data on the development of the predatory wasp Symmorphus allobrogus (Hymenoptera, Vespidae) to test the hypotheses that sexual differences of growth resulting in the female-biased SSD embrace the difference in (1) the egg size and the starting size of larva, (2) the larval development duration, and (3) the larval growth rate. We found that eggs developing into males and females have significant differences in size. There was no significant difference between the sexes in the duration of larval development. The relative growth rate and the food assimilation efficiency of female larvae were significantly higher than compared to those of male larvae. Thus, the SSD of S. allobrogus is mediated mainly by sexual differences in egg size and larval growth rate.

The application of trap-nests for the studies of cavity-nesting Hymenoptera eventually implies a need for immediate nest identification using its structure. Possible nest characters that may be potentially useful for the separation of closely related species are body size-dependent metrical parameters of brood cells. We studied the dependence of brood cell length on nesting cavity width in ten cavitynesting predatory wasp species. Five hypotheses were tested. We calculated the derived parameters of brood cells needed for testing the hypotheses and, applying correlation and linear regression, assessed the degree of fit of the actual data to the hypothesized dependences. In three studied wasp species, the dependences of cell length on nesting cavity width in the datasets of cells with the brood of different sex supported different hypotheses. The results of the study demonstrate that species-specific metrical differences between related species, if present, are likely to be found in the length and width of a cell, but not in its volume.