SIZE AND MATING SUCCESS IN A NON-TERRITORIAL DAMSELFLY XANTHAGRION ERYTHRONEURUM (ZYGOPTERA: COENAGRIONIDAE)

Abstract

Flight activity and reproductive behaviour of the damselfly Xanthagrion erythroneurum (Zygoptera: Coenagrionidae) was observed over a 2 year period (1989-1990). Marked insects were censused hourly between 0900-1600 hs each day for 6 weeks in each year where, in addition to presence or absence, records were made of individual behaviour including mating and oviposition. Evidence for male-male behaviour was tested using models of both sexes. All observations and experiments were conducted at a focal pond close to Perth, Western Australia. Sex ratios of damselflies visiting the pond were male biased; males tended to arrive at the pond ahead of females. Sexual maturity, as indicated by the first attempts to mate were measured for both sexes. Both sexes matured within 8 days from emergence. Daily survival rate was estimated by the number of times individuals returned to the focal pond. Conservative estimates of survival were 80% for males and 70% for females. Males showed no signs of agonistic behaviour either towards other flying or perched males or towards the models of either sex. X. erythroneurum showed no signs of territorial behaviour. Mating behaviour involved males intercepting perched of flying females. Pairs adopted the tandem and wheel positions typical of all odonates. Oviposition immediately followed mating. Males remained with the submerged females or on the surface of the water close to the submerged female. Females remained underwater for an average of 35 mins. On emergence other males attempted to copulate with the female, adopting the tandem position for several minutes. No successful copulations were observed and males released the previously mated female within minutes. Althought age had a significant effect on mating success, size (head width and wing length) of adult males and females had no effect on mating success. Both males and females close to 7 days post-emergence had the greatest chance of mating.