Pygidial defensive titer and population structure ofAgabus bipustulatus L. andAgabus paludosus F. (Coleoptera, Dytiscidae).

Aromatic pygidial gland constituents ofAgabus bipustulatus L. andA. paludosus F. were quantitatively determined. Concentration fluctuations were found to be dependent on age and season. Both in quantity and quality of the secretion, young beetles differ from mature beetles by storing only small amounts of gland material with different portions of constituents. Seasonal variations are mainly due to the changing population structure of the species.