Effect of population density and photoperiod on larval growth and reproduction of Tenebrio molitor (Coleoptera: Tenebrionidae)

The mealworm Tenebrio molitor (Coleoptera: Tenebrionidae) is the most consumed insect in the world. This study aims to optimize the space in the mass-rearing facilities of this insect, as well as to evaluate the effect of photoperiod on the reproduction and growth of the larvae. The two cross-over factors studied were photoperiods regimes (8L:16D and 0L:24D) and four density treatments (0.25; 0.75; 1; 1.5 ind/cm2) under rearing conditions of 28 ± 1 °C and 70 ± 5%relative humidity. Statistical analysis showed that density and photoperiod (P > 0.05) had no effect on pupal development. Moreover, population density and photoperiod had no effect on pupal development and adult survival. However, average fertility was affected by population density and the optimal population density was 0.25 adults/cm2.Photoperiod had no effect on the fertility of T. molitor. Regarding total fecundity, there is no interaction between the two factors. The fecundity of T. molitor was significantly affected by population density. The highest fecundity was obtained at 1.5 adult/cm2. The optimal combination of photoperiod and density for larval development was of 0.25 ind/cm2 with 8 h of light per day. The conversion rate was not affected by the factors studied. These findings enable to optimize the mass-rearing of T. molitor and reduce the cost and environmental impact of these facilities.