The Effects of Density on the Growth and Temperature Production of Tenebrio molitor Larvae

Abstract

Tenebrio molitor larvae live, at least partially, inside their feed. Hence, they do not live on a 2D plane but in a 3D environment. However, previous studies mainly focused on the optimal number of larvae for a given surface area, not the available volume. The goal of this study was to assess the growth and survival of mealworms in a standardized semi-industrial setting with a varying density (cm3) and substrate height. A full factorial experimental design was used with five larval densities (0.5–8 larvae/cm3) and four feed heights (1–8 cm) in 60 × 40 cm crates. Furthermore, the in-crate temperature was monitored and linked to the density. The results of this study clearly indicate that mealworm larvae prefer a low density (cm3). At low larvae densities, the substrate height was less important, with a slight preference for a thicker layer. In contrast, at high(er) larval densities, a lower layer thickness resulted in better growth. The in-crate week temperature varied up to 14 °C (25–39 °C) between treatments and could be predicted well based on the number and size of the larvae. These results may help the industry to improve their production efficiency in terms of larvae density, substrate height and room temperature.

Farmed Yellow Mealworm (Tenebrio molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry

“…YML often aggregate within their feeding substrate; this may increase the local temperature via metabolic heat production by > 10 ℃ for late-stage larvae (Michal, 1931a;Morales-Ramos and Rojas, 2015). When combined with the insulating effect of the substrate, these localized hot spots could be lethal at high densities (e.g., an in-crate temperature of 43.9 ℃ was reported in Deruytter et al 2022). Changing substrate textures and crate materials may allow for more rapid heat dissipation, protecting larvae from overheating.…”

Viral and fungal pathogens in house cricket rearing : Effects of temperature, density and co-infection

“…For B. bassiana isolates, no significant differences were detected, but the isolate KVL 97-44 caused the highest mortality and was selected for use in the co-stressing experiments. The choice of rearing density is a crucial decision for insect rearing [66] and especially for cricket producers. The aim is to maximize the biomass produced in the available rearing space, but at the same time to avoid unnecessary losses due to crowding in the facilities.…”

“…Density of crickets in the rearing is a crucial factor to avoid crowding-related stresses. Density has been well studied for other insect species [65,66], but in the case of crickets, only a few studies address the topic [67][68][69]. During the development from pinheads to fully-grown adults, the cricket body mass increases from 0.7 mg to 300 -500 mg of adult live body weight.…”

“…Optimal densities combined with optimal growth temperatures resulting in the highest yields per batch are favourable from a commercial production perspective. Unlike other mass-reared insect species [65][66][67]81], only a few studies investigated optimal rearing densities and temperatures for house crickets [67,68]. To 12 date, it is unknown if there is a correlation between rearing density, temperature, and the abundance of the AdDV.…”

“…Elevated rearing densities have negative effects on production parameters, as shown for other mass-reared insect species such as the black soldier fly [117]. For other species, such as the yellow mealworm (Tenebrio molitor L.), the best growth was achieved at a relatively low density (0.5 larvae/cm 3 ) [66]. Therefore, similarly assessing the possible effects of cricket rearing density on the survival, individual biomass and total biomass produced is highly important to optimize the production.…”