Base (Lower Developmental) Threshold
Definition
The temperature below which an insect species does not develop. For forensically important blow flies in temperate regions this typically ranges from approximately 1 to 10 degrees Celsius, varying considerably by species: cold-tolerant species such as Calliphora vicina have been estimated as low as 1 degrees Celsius in some populations, while common temperate species such as Lucilia sericata have biological minima between 7.5 and 10 degrees Celsius.
- Also called
- Base threshold, lower developmental threshold
- Typical range
- Approximately 1 to 10 degrees Celsius
- Cold-tolerant example
- Calliphora vicina, near 1 degrees C in some populations
- Warmer-adapted example
- Lucilia sericata, 7.5 to 10 degrees C
Common questions
Why does the base threshold vary so much between species?+
It reflects each species' evolved climate range: cold-adapted flies active in early spring or higher latitudes have evolved a lower minimum for development, while species suited to warmer conditions need a higher temperature before development starts at all. Using the wrong species' threshold in a PMI estimate can shift the calculated interval substantially.
How does the base threshold get used in a real case calculation?+
It sets the zero point for accumulated degree day or degree hour calculations: only the temperature above this threshold on each day counts toward insect development, so the threshold has to be identified correctly for the species present before any degree-day sum is meaningful.
Related terms
- Accumulated Degree Days (ADD)
- The sum of daily mean temperatures above a threshold (usually 0 °C) over a period of interest. Used as a measure of...
- Accumulated Degree Hours (ADH)
- A temperature-corrected measure of developmental time. Calculated by summing (hourly ambient temperature minus the species-specific base temperature threshold) across the period of...
- Scene Correction Factor
- A temperature offset derived by comparing data-logger readings at the scene with concurrent weather-station readings, then applied retrospectively to station historical data...
- Thermal-Summation Model
- The linear model that relates insect development rate to temperature above a threshold. Development rate increases in proportion to the excess temperature;...
- Upper Developmental Threshold
- The temperature above which development decelerates. Between base and upper threshold the thermal-summation model is approximately linear; outside this range it breaks...