Sex ratio is the proportion of females among offspring, written as the female fraction or as female:male. Spider mite and thrips populations are usually female-biased in lab life tables, and parthenogenetic aphids indoors are all female.
In practice
Only females lay eggs, so life tables include sex ratio when computing r_m and R0. A population that shifts toward males grows more slowly. Predators that eat mainly eggs and young nymphs cut future females directly.
Don't confuse with
- Fecundity: eggs per female, before applying the sex ratio.
Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms.Slender insects about 1-2 mm long, chiefly western flower thrips (Frankliniella occidentalis), that rasp leaf surfaces, leaving silvery streaks dotted with black frass.A record of survival and egg-laying at each age for a cohort of pests at set conditions, from which development time, fecundity and r_m are calculated.Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.The average number of female offspring a female produces in her lifetime after mortality: the population's multiplication per generation.The number of eggs or live young a female produces, per day or in her lifetime; a key life-table input.Reproduction in which unmated females lay unfertilised eggs that become males, while mated females make both sexes. Typical of spider mites and thrips.A sex-determination system where males develop from unfertilised eggs with one chromosome set and females from fertilised eggs with two; found in mites, thrips and whiteflies.
