Generation time is the mean age at which females produce their offspring, from a life table. It is longer than egg-to-adult development, because females need a pre-oviposition period and lay over many days. For two-spotted spider mites it is roughly one to two weeks at 25 C in lab studies, shorter in heat.
In practice
Generation time drives control intervals. A spray or release that misses eggs must be repeated before the survivors mature and lay, which means within one egg-plus-immature period at your temperature. Degree-day thresholds let you convert one temperature's generation time to another's.
Don't confuse with
- Doubling time: how long numbers take to double, much shorter than a generation.
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.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.A unit of accumulated heat above a pest's lower developmental threshold; development finishes when a stage's degree-day total is reached, whatever the calendar says.The days an unchecked pest population needs to double, equal to ln 2 divided by r_m (0.693 / r_m).The per-day rate at which an unchecked pest population multiplies under set conditions, from a life table; N(t) = N0 x e^(r_m x t).
