The effect of relative humidity on the survival and growth rate of the yellow mealworm larvae (Tenebrio molitor, Linnaeus 1758)

The current livestock sector is a large contributor to the environmental challenges facing the world. To reduce the environmental impact of food production, a change of the sector is necessary. Entomophagy could be a step towards a more sustainable protein production. However, the insect farming community has a short history compared to conventional livestock, thus, it lacks knowledge of how a profitable mass production of insects is established. In this study we aimed to find the optimal relative humidity (RH) for production of larvae of a popular species for insect farming; the yellow mealworm,Tenebrio molitor. More specifically we tested the effect of a RH of 43, 51, 68, 75 and 84% on the survival rate, mass and length ofT. molitor larvae, from hatching and two weeks forward. Control of RH was achieved using the saturated salt solution method, and the temperature was kept at 30 °C. Experiments were carried out over 12 weeks. The sample size was 100 larvae and eight replicates per treatment. Results showed that the RH had no effect on larval survival rate but had a significant effect on individual larvae mass and length after three weeks. Larval mass and length increased with humidity, and larvae reared at a RH of 84% were 1.96 times heavier and 1.31 times longer than larvae raised at 43%. Hence, for an industrial mass producer ofT. molitor larvae, applying close to the optimal RH of 84% would likely result in an increased larvae size at harvest and a faster growth rate, ultimately leading to a higher yield.