The effects of density on the growth, survival and feed conversion of Tenebrio molitor larvae

An appropriate stocking density is beneficial to run an efficient business and improve animal welfare. In most traditional livestock this is defined as the number of animals per area. However, the larvae of the mealworm (Tenebrio molitor), one of the most important commercial insects, live both on top and inside their feed. In this study we assessed if different areal stocking densities (2D, range 0.6-10.4 larvae/cm(2)) resulted in a different growth rate and feed efficiency when the volumetric stocking density remained constant (1 larvae/cm(3)). In a first experiment the larvae received wheat bran once at the start, but in the second experiment wheat bran was added throughout the experiment to ensure that the larvae remained at 1 larvae/cm(3). The results indicate that, given a stable volumetric density, the areal density can vary between 0.6 and 10.4 larvae/cm(2) without extreme variation in growth, survival or feed efficiency. The lowest assessed densities did result in a slightly lower average weight and yield. A maximum yield per volume of feed was observed at 2.5 larvae/cm(2) (feed conversion ratio (FCR) of 1.76 dry feed/live larvae). Yet, the overall highest yield was observed at 10.4 larvae/cm(2) as the increased areal density far outweighed the slight decrease in FCR. In conclusion: when mealworm larvae are provided with an equal volume of wheat bran the influence of areal density is low and could be as high as 10.4 larvae/cm(2) for optimal yield.