# Developmental threshold

> The temperatures below which (lower) and above which (upper) a pest's development stops or slows; they bound degree-day models.

- Canonical: https://genetixbay.com/knowledge/glossary/developmental-threshold.html
- Also written: lower developmental threshold, upper developmental threshold, base temperature, lower threshold, upper threshold, thermal threshold
- Glossary category: Pests and diseases · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

The lower developmental threshold is the temperature at which development halts; the upper threshold is where it slows or stops because heat becomes harmful. Lower thresholds are usually estimated by extrapolating a straight line of development rate against temperature down to zero. For many greenhouse [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and insects the lower threshold sits around 8-12 C and the upper around 32-40 C, but each species and stage differs.

## In practice

Between the thresholds, warmer means faster generations. Near the upper threshold, mortality and egg failure rise, so the fastest growth (highest r_m) usually sits a few degrees below it. Grow rooms at 24-30 C sit right in the fast zone for spider mites, [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and [aphids](https://genetixbay.com/knowledge/glossary/aphid.md). Indoor nights rarely drop below a pest's lower threshold, which is why indoor populations never pause.

## Don't confuse with

- **Critical thermal limit**: the temperature that kills, not just stops development.
- **Diapause**: a programmed dormancy, triggered by [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) as well as temperature.

## Related terms

[Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Diapause](https://genetixbay.com/knowledge/glossary/diapause.md)

## Read more

- [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md)

## Sources

1. UC IPM. Degree-Days: About Degree-Days. University of California ANR. https://ipm.ucanr.edu/WEATHER/ddconcepts.html