FREQUENCY OF FEMALE MORPHS IS RELATED TO AN INDEX OF MALE DENSITY IN THE DAMSELFLY, NEHALENNIA IRENE (HAGEN)

Researchers have questioned whether variation in population density in fluences the maintenance of two or more morphs within and between inse ct populations. Two distinct morphs of female Nehalennia irene (Hagen) (Odonata: Coenagrionidae) occurred at each of eight sites in eastern Ontario, Canada; one morph (i.e. andromorph) was coloured and patterne d like the conspecific male. We found significant differences in relat ive frequencies of andromorphs and in male density between sites; freq uency of andromorphs ranged from 2-28% and was positively correlated w ith male density. Sites with high densities of males were located clos er to low-density sites than to other high-density sites, indicating t hat high-density sites were somewhat independent of one another. We al so found spatial variation in density of males within sites; males wer e present almost exclusively at edges of ponds or marshes. Proportiona lly more andromorphs than heteromorphs were found at the edges of site s, where male-female interactions were likely frequent. Sex ratios at the edges of sites were most strongly male-biased at two of three high -density sites, indicating that males may force non-receptive females away from the edge of high-density sites. Spatial and temporal variati on in male density of N. irene may be an important factor influencing morph coexistence.