Effects of local density on fecundity and mating speed for periodical cicadas.

Abstract

The relationship between local density of adult periodical cicadas (Magicicada septendecim) and fecundity was investigated at 3 sites in 1979 and 6 sites in 1980. In 1979, a sample taken 9 days after the emergence peak showed no significant differences in the number of vitellogenic follicles contained by females from the three sites. A later sample, taken 22 days after the emergence peak, revealed significant between-site differences in the number of follicles per female. Individuals from the densest site contained over 50% more follicles than females from the lowest density site. In 1980, there was again a significant between-site difference in fecundity. Females from sites of higher density contained more follicles than females from less dense sites.The rate at which females mated was independent of local adult density. At all sites, most females had successfully mated by the end of the emergence period. All females required at least 5 days and usually longer before mating and ovipositing.Earlier work demonstrated that the ratio of offspring: adults was greater at sites of higher emergence density than at low lensity sites. The pattern of inverse density-dependent fecundity, reported here, undoubtedly contributes to this effect. However, density dependent mating speed does not appear to contribute to this effect.