Isomegalen Diagram
Definition
A contour plot with temperature on the y-axis and age on the x-axis, where each contour line connects all (temperature, age) combinations that yield the same larval body length. Reading across from a known temperature to the measured length contour gives the larval age.
- X-axis
- Age
- Y-axis
- Temperature
- Contour meaning
- Equal larval body length
- Used for
- Estimating larval age from length and temperature
Common questions
How does an isomegalen diagram differ from an isomorphen diagram?+
The isomegalen diagram plots contours of equal body length against temperature and age and is read from a measured length, while the isomorphen diagram plots contours of equal developmental stage and is read from an observed morphological stage. They give cross-checking estimates from different kinds of measurement on the same specimen.
Why does the diagram need a temperature value rather than just larval length?+
Larval growth rate is strongly temperature-dependent, so the same length can correspond to very different ages depending on how warm the rearing conditions were. The diagram lets the examiner read off an age only after fixing the temperature the larvae actually developed at.
Related terms
- Isomorphen Diagram
- A contour plot of the same axes where each contour connects all (temperature, age) combinations that produce the same morphological developmental stage...
- 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...
- 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...