Comparison of the habitat and population structure of Ischnura elegans (Vander L.) and I. pumilio (Charp.) in a central Netherlands locality (Zygoptera: Coenagrionidae)

The field observations carried out systematically (1978, 1979) at the locality "Steengroeven”, near the village of Winterswijk (Gelderland Prov.), which supports a population of some 400 individuals of I. elegans and 800 of pumilio, yielded (preliminarily) the following evidence: (I) I. pumilio prevails in the grassland habitats, while elegans mainly occurs in the Typha vegetation; (2) I. pumilio is on wings earlier in the season and in greater numbers than elegans; the balance in numbers is achieved early in August, while in the late summer /. elegans-is dominant and its adult season considerably exceeds that of pumilio; (3) I. pumilio requires higher atmospheric temperatures than elegans, hence its activity commences later in the day than that of the latter species; (4) during the rain pumilio completely disappears from sight, while the elegans individuals may still be active. It is likely that there are some distinctions in the sexual behaviour between the two species, but our evidence on this aspect is insufficient.