Isomorphen Diagram
Definition
A contour plot of the same axes where each contour connects all (temperature, age) combinations that produce the same morphological developmental stage (instar boundary or pupariation). Staging rather than measuring the larva gives the input.
- Tool type
- Contour plot (temperature vs. age with developmental stage lines)
- Input
- Larval developmental stage (visual assessment, not body measurement)
- Output
- Development duration at a known constant temperature
Common questions
What does an isomorphen diagram show?+
An isomorphen diagram is a contour plot that maps how blow fly development works at different temperatures and ages. Each line on the diagram connects all the temperature and age combinations that produce the same developmental stage, like an instar boundary or the point where a larva pupariates. You read the diagram to find out how long development takes at any given constant temperature.
How do you use an isomorphen diagram in the field?+
You stage the larva (identify which developmental stage it is) without measuring it, then plot that stage on the diagram with the actual temperature where it was found. The diagram tells you how old the larva is at that temperature. This is the key step in estimating time since death from insect evidence.
Why use an isomorphen diagram instead of just measuring the larva?+
Staging by developmental markers is more reliable than body measurements, which vary with nutrition, sex, and species. The diagram lets you translate what you see (the stage) and what you know (the temperature) into an age estimate. Different fly species have different diagrams, so you use the right one for the species you find.
Related terms
- Development Table
- A species-specific reference dataset giving the accumulated temperature (degree hours or degree days above a threshold) required to complete each life-stage transition....
- Eclosion
- The emergence of the adult fly from the puparium. In rearing, the date of eclosion is recorded as the end point of...
- Isomegalen Diagram
- A contour plot with temperature on the y-axis and age on the x-axis, where each contour line connects all (temperature, age) combinations...
- Larval Instar
- One of three larval stages (L1, L2, L3) separated by moults. Each instar has distinctive mouth-hook and posterior spiracle morphology that allows...
- Larval Length (Body Length)
- The maximum extended length of a blow fly larva, measured from the anterior tip to the posterior end in freshly killed or...
- Minimum Base Temperature
- The temperature below which blow fly larval development effectively stops. This threshold varies by species: Lucilia sericata is typically around 9 degrees...
- Pupariation
- The process by which the third-instar larva contracts and hardens its own cuticle to form the puparial case (puparium) that encloses the...
- Rearing Medium
- The food source placed in the rearing container to support larval development. Raw beef liver is the standard; it provides protein, moisture,...
- Rearing Temperature
- The constant or mean temperature at which a larval cohort was held in the laboratory experiment that generated the developmental dataset. The...
- Thermal Constant (K)
- The total ADD or ADH required to complete a developmental phase from egg to a defined endpoint. Different from the isomegalen approach...
Explained in these topics
- Larval Age and Development: Isomegalen and Isomorphen DiagramsA contour plot of the same axes where each contour connects all (temperature, age) combinations that produce the same morphological developmental stage (instar...
- Rearing Immature Insects to the Adult StageA graphical representation of blow fly development rate against temperature, showing the lines of equal developmental stage. Used to read off development durat...