So far it has been regarded that Ischnura spp. is univoltine species in Poland. In 2010 the situations pointing out the emergence of the second generations were observed. In 2011 the studies designed to provide this evidence were conducted. A new and isolated pond (2x2 m, depth to 40 cm) was created in March in order to eliminate the possibility of the emergence of the first generation. It was situated near two shallow water bodies where in 2010 the larvae of Ischnura pumilio were found. In 2011 dynamics of the population in the new pond, two near shallow water bodies as well as in one large and deep water body were studied. The results confirmed the second generations of both species in the new pond and two shallow water bodies in its vicinities. Data from the large and deep water body did not confirm the emergence of the second generation of Ischnura elegans but also did not deny it. Metamorphoses lasted from the beginning of May till the end of August, with the peak in the second half of May. The time of larval development could be elongated by different water temperature than in small water bodies. However, the length of the development in experimental conditions at the temperature of 20–27°C is 60–70 days, and these temperatures prevailed for most of the season in the shore zone of this water body. Therefore, one can not exclude the possibility of development of the second generation in it – especially that it would explain the period of metamorphoses lasting up to four months. The full development of the second generation of Ischnura pumilio in the dug up pond lasted up to 60 days. This is the shortest development time found in the wild in Central Europe, similar to that of the development of I. pumilio in southern France, and the data from the breeding of other species of the genus (I. verticalis – 58 days, I. elegans – 60–70 days). The time of full development of the second generation of I. elegans in this water body was up to about 100 days. However, this water body was colonized by I. elegans reluctantly and the result may be unrepresentative. The time of development of the second generation of I. elegans may be much shorter, as indicated by the population dynamics in a shallow water body situated near the dug up pond. Data obtained during the research and a number of late records of I. pumilio indicate that the occurrence of the second generation of this species does not belong in Poland to rare exceptions. The arrangement of late records rather indicates the possibility of the emergence of the second generation in a large distribution area of the species in the country. Few observations of individual juveniles of I. pumilio in the half of September, and in one case 17 days after the record of the last juvenile specimen at the site, indicate the real probability of the emergence of even the part of the individuals of the third generation which requires further study.
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.