Sperm number

Theory predicts that an increased number of sperm is advantageous in sperm competition, either because a larger ejaculate volume displaces more rival sperm or due to numerical superiority. In general, sperm competition favouring numerous sperm may have led to the evolution of many tiny sperm and may even be responsible for the evolution of the two sexes (Parker et al., 1972 Bulmer and Parker, 2002). Comparative data in numerous animal groups have corroborated this finding. Males invest more...

References

Alcock, J. (1994) Post-insemination associations between males and females in insects the mate-guarding hypothesis. Annual Review of Entomology 39, 1-21. Andersson, J., Borg-Karlson, A.-K. and Wiklund, C. (2000) Sexual cooperation and conflict in butterflies a male-transferred anti-aphrodisiac reduces harassment of recently mated females. Proceedings of the Royal Society of London, Series B 267, 1271-1275. Andersson, J., Borg-Karlson, A.-K. and Wiklund, C. (2003) Antiaphrodisiacs in pierid...

Densitydependent prophylaxis

Most pest species of insects, almost by definition, exhibit wide fluctuations in population density from one generation to the next when conditions are favourable, population densities are high, and when they are less favourable they are low. For example, population densities of the larch budmoth (Zeiraphera diniana), a lepidopteran forest pest, may vary by more than 20,000fold over five generations (Speight et al., 1999). Low- and high-density environments differ in a number of qualitative and...