Accumulated Degree Hours (ADH)
Definition
A temperature-corrected measure of developmental time. Calculated by summing (hourly ambient temperature minus the species-specific base temperature threshold) across the period of interest. Insect development is mapped to ADH rather than calendar time because metabolic rate is temperature-dependent.
- Calculation
- Sum of (hourly temperature minus species-specific base temperature) across each hour of development
- Primary use
- Converting insect developmental stage to calendar time (post-mortem interval estimation)
- Key organisms
- Blow flies (terrestrial remains) and aquatic insects (submerged remains)
- Resolution advantage
- Hourly resolution (finer than daily accumulated degree days) in variable climates
Common questions
How do forensic entomologists use ADH to estimate time of death?+
Entomologists measure the insect's current development stage, then divide the thermal threshold needed to reach that stage by the mean hourly temperature above the species-specific base temperature. This calculation converts the insect's developmental progress back to elapsed calendar time. Temperature records from the scene are essential to make this back-calculation accurate.
Why is ADH better than calendar time for blow fly development?+
Blow flies develop at different rates depending on temperature. ADH normalizes across temperature variation by accounting for only the thermal energy above a species' base threshold. This means an insect developing in a cold room takes longer than one in a warm room, even if the same calendar days pass. ADH captures this biological reality where calendar hours cannot.
What's the difference between ADH and accumulated degree days (ADD)?+
Both measure thermal development above a base temperature. ADD sums daily totals, while ADH sums hourly totals. ADH gives finer resolution and is now preferred in cases with hourly temperature data, especially in climates where temperature swings widely between day and night.
Related terms
- Instar
- A developmental stage between moults (ecdysis). Blow flies have three larval instars (L1, L2, L3), each ending when the larva sheds its...
- Entomotoxicology
- The analysis of insect tissue for drugs and toxins when decomposition has made conventional biological fluids unavailable. Blow-fly larvae feeding on a...
- Minimum PMI (PMImin)
- The shortest interval consistent with the entomological evidence. In practice this is what entomologists estimate: a floor on elapsed time based on...
- Post-Mortem Interval (PMI)
- The time elapsed between death and discovery or examination of remains. PMI estimation draws on multiple disciplines: soft tissue decomposition stage, insect...
- 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...
- Aquatic Succession
- The predictable sequence in which aquatic invertebrate species colonise submerged remains, analogous to the terrestrial blowfly succession but driven by different taxa...
- Base (Lower Developmental) Threshold
- The temperature below which an insect species does not develop. For forensically important blow flies in temperate regions this typically ranges from...
- Base Temperature
- The species-specific temperature below which development effectively ceases. For most forensically relevant blow fly species this is in the range of 2-10...
- Binomial Nomenclature
- The two-part Latin naming system established by Linnaeus: genus name followed by species epithet. Used in all scientific and forensic botanical reports...
- Calliphoridae
- The blowfly family: metallic-coloured flies that are typically the earliest colonisers of exposed remains. Forensically important genera include Calliphora, Lucilia, Chrysomya, and...
- Chironomidae
- Non-biting midges whose blood-red larvae (bloodworms) are among the earliest colonisers of submerged organic matter. Their development rates are temperature-dependent and well...
- COI Barcoding
- DNA-based species identification using a standard 658 bp segment of the mitochondrial cytochrome oxidase subunit I gene. Sequences are matched against reference...
Explained in these topics
- Temperature, Accumulated Degree Days and Degree HoursThe hourly equivalent of ADD: each hour contributes (hourly temperature minus base temperature) degree-hours when temperature exceeds the base. ADH gives finer...
- Aquatic Forensic Entomology and Submerged RemainsThe thermal equivalent of accumulated degree days, used for shorter PMI windows. Calculated by summing (water temperature in °C minus a species-specific base t...
- Entomological Evidence and Post-Mortem Interval EstimationA temperature-corrected measure of developmental time. Calculated by summing (hourly ambient temperature minus the species-specific base temperature threshold)...
- Sources of Error and Uncertainty in Entomological PMIThe total thermal energy above a species' developmental base temperature, summed over time. The foundational calculation in blow fly larval ageing: divide the...
- Forensic Entomology Casework and Scene InterpretationThe sum of temperature-time units above a species-specific developmental threshold, used to convert insect stage into calendar time. A species reared at higher...
- Insect Biology and Taxonomy for the Forensic EntomologistA measure of thermal development: temperature above a threshold, summed over time. Forensic entomologists use ADH or accumulated degree days to translate a dev...
- The Blow Fly Life Cycle: Egg to AdultThe sum of (temperature minus base temperature) across each hour of development. ADH is the standard unit for forensic blow fly development calculations becaus...