Aspects of demography in Lestes barbarus (Fabr.) and L. virens vestalis Ramb. (Zygoptera: Lestidae)

Mark-release-recapture data of 3 single-pond populations of L. barbarus and I of L. virens were worked out to estimate: consistence of populations at emergence and at the egg stage, sex ratios at emergence and in the reproductive period, pre-reproduction period duration, survival in the field and dispersal of females in respect to males. On the basis of critical considerations, sex ratio at emergence is suggested to be 1:1. while in the reproductive period it is male-biased. The length of the pre-reproductive period is widely variable in L. harharus. while in L. virens it falls within the range of the former. By comparing the length of the pre-reproductivc period of L. virens populations from central Europe with that of those in central Italy, it is suggested that there is a correlation between latitude and pre-reproductive period length in this sp. as is also known in other lestids. Survival rate in the field was lower in the reproductive than in the pre-reproductive period, probably due to heavier predation in the former. Females dispersed more than males, dispersal rates being w idely variable in different samples and years. Evidence of dispersal in leneral rather than in mature damsclflies suggests that colonization of new ponds may occur as a consequence of earlier acquaintance with flooded ponds, w hich can induce the damselflies to home to the new pond after maturation.