Sexual size dimorphism and sex‐specific survival in adults of the damselfly Lestes disjunctus

1. A population of adult Lestes disjunctus (Odonata: Lestidae) was studied in eastern Ontario, Canada. Mass at sexual maturity and activity rates of individuals were measured. Population density was estimated on transects, while survival rates and population size were estimated using mark−recapture methods. 2. There was no difference in mass of mated and unmated males. Females were more than 50% heavier than males, and were also more active than males. 3. Males were almost eight times more abundant on transects than females, but Manly−Parr estimates of male population size were only a maximum of 2.5 times larger than estimates for females. 4. Males were 2.5 times more likely to be resighted after marking than were females. This accounts for much of the discrepancy between transect estimates and mark−recapture estimates of relative population size. 5. Daily survival rates of sexually mature females were not significantly less than those of males, and therefore cannot account for a change in sex‐ratio from 1 : 1 at emergence to more males than females in sexually mature adults. 6. Differences in mortality must occur prior to sexual maturity, coincident with the time during which differences in mass gain are also taking place.