Soldier production strategy in lower termites: from young instars or old instars?

We constructed a mathematical model to explain from which instars soldiers should be produced to maximize the growth rate of a termite colony. The model is based on the demography of the lower termite's colony: many of them feed inside the nest. The model predicts the following: (1) When the colony is young (it still has enough food and needs a high ratio of soldiers to workers) it will produce soldiers from young instars. (2) When the colony is old (it does not have enough food any more and needs a lower ratio of soldiers to workers) it will produce soldiers from old instars. This prediction fits well with the fact investigated by past empirical researches. With the samples of colonies of Neotermes koshunensis, we measured the antennal joint number of soldiers of each colony. We plotted the antennal joint number (1) of the average and (2) of the maximum one for each colony, against the total number of colony members. For both in each colony, we confirmed the consistency between the model and the samples: as the colony matures, it produces soldiers from older instars. The model also explains why higher termites produce soldiers from fixed instars. Their life style, in which they go outside to collect food, does not require a change in their soldier production strategy.