In poikilotherms, developmental time and adult lifespan are biological traits driven by temperature although their underlying physiological mechanisms differ. The developmental theory of ageing predicts a positive correlation between these two traits without confirming a genetic or causal relationship. The developmental rate isomorphy hypothesis established that the proportionality in the duration of each pre-imaginal stage with respect to total developmental time does not vary with temperature. This may have important evolutionary implications. We conducted an analysis with arthropods of agronomic interest to study if the hypothesis could be extended to the total lifespan of poikilotherms, including adult lifespan. We showed that isomorphy could be acceptable for a global description of this relationship. However a general model of power law type is more appropriate for characterizing the relationship between developmental time and adult lifespan. In this model, the shape of the curve is a constant characteristic, but the parameters that control it depend on the functional type of the arthropod (phytophagous, predator or parasitoid). Presumably this power law could be extended to all arthropods of agricultural interest, and more generally to all arthropod.