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

Abstract

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 of T. 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 of T. 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.

Determination of Moisture and Protein Content in Living Mealworm Larvae (Tenebrio molitor L.) Using Near-Infrared Reflectance Spectroscopy (NIRS)

“…The results show that the relative humidity has a significant impact on larval composition and the biomass of the individual larvae, but it does not affect the survival rate at optimal rearing temperatures. This was also observed in other studies [ 20 , 21 ]. Larvae reared on dry wheat bran grew much more rapidly when pure water or carrots were available than when they were not, and the larvae showed highly significant differences in their specific growth rates.…”

“…Several studies showed that the nutritional composition of the feeding substrate has an influence on insect larval composition [ 7 , 17 , 18 , 19 ], and relative humidity also has an impact on the survival, growth rate and life cycle of Tenebrio molitor . Humidity over 70% showed the best results for larval development, survival and growth [ 20 , 21 ]. In order to ensure balanced and targeted feeding or to achieve a desired larval composition, it is essential to monitor and regulate larval feeding and water supply.…”

Entomoponics: combining insect rearing and greenhouse vegetable production – a case study with Tenebrio molitor and high-wire cucumber cultivation

“…A similar heating strategy could be used in mealworm production as 26% of total energy demand is required to keep the rearing facility at the desired temperature (Oonincx and De Boer, 2012). Mealworm growth in the greenhouse may have benefitted somewhat from a higher ambient relative humidity (74.5% in the greenhouse compared to 60% under controlled climate) as a higher relative humidity is associated with faster growth (Johnsen et al, 2021).…”

Exploiting Agri-Food Waste as Feed for Tenebrio molitor Larvae Rearing: A Review

“…In more detail, TM larvae are recommended to be reared at high temperatures, in a temperature range of 25-27.5 • C [15,61,62]. Furthermore, a very high relative humidity is also required for proper rearing, with an optimum range between 60 and 75% [56,63,64]. However, despite the high relative humidity required in the environment for the growth and development of larvae, low moisture is required within the feeding substrate [65].…”