Physical Properties of Substrates as a Driver for Hermetia illucens (L.) (Diptera: Stratiomyidae) Larvae Growth

Abstract

The growth and nutritional profile of the black soldier fly larvae (BSFL) is usually investigated and compared when the larvae feed on substrates that differ in the chemical composition as well as physical properties. This study compares BSFL growth on substrates that differ primarily in physical properties. This was achieved by using various fibres in the substrates. In the first experiment, two substrates with 20% or 14% chicken feed were mixed with three fibres (cellulose, lignocellulose, or straw). In the second experiment, the growth of BSFL was compared with a 17% chicken feed substrate that additionally contained straw with different particle sizes. We show that the substrate texture properties values did not influence the BSFL growth, but the bulk density of the fibre component did. The substrate mixed with cellulose led to higher larvae growth over time in comparison to substrates with higher bulk density fibres. BSFL grown on the substrate mixed with cellulose reached their maximum weight in 6 days instead of 7. Neither the fibres nor the nutrient level changed the crude protein content of BSFL and the values ranged between 33.5% and 38.3%, but an interaction between the fibre and nutrient level was observed. The size of straw particles in the substrates influenced the BSFL growth and led to a 26.78% difference in Ca concentration, a 12.04% difference in Mg concentration, and a 35.34% difference in P concentration. Our findings indicate that the BSFL-rearing substrates can be optimised by changing the fibre component or its particle size. This can improve the survival rate, reduce the cultivation time needed to reach the maximum weight, and alter the chemical composition of BSFL.

Hermetia illucens (Diptera: Stratiomyidae): Need, Potentiality, and Performance Measures

“…The performance of larvae could be influenced by the aeration within the substrate which in turn depends on the stickiness [21], viscosity [77], particle size [28,78], and physical properties of the feed, such as its fibrous nature [79]. The particle size range described in the literature includes 0.1-1.5 mm [75], ~0.4 mm [33], ≤1-15 mm [80], ~1 mm [63], ~5 mm [81], 4.00-6.35 mm [78], 1-2 cm [23], and ≤3.8 cm [82]. According to Dortmans et al (2017), the substrate has to be shredded to a particle size of at least less than 1-2 cm in diameter [23].…”

“…The authors explain that the increased access of the feed to microbes and reduced oxygen transport are assumed to be reasons for lower larval weight with a smaller particle size [78]. Yakti et al (2023) found that the larval weight reduced from ~125 mg FM to ~75 mg FM as the straw particle size decreased from >3 mm to ≤1 mm [80]. Usage of a blended substrate could result in less accessibility of feed for the larvae due to high feed compactness and lower oxygen levels at the bottom of the rearing box forming anaerobic zones harboring corresponding microbiota [61].…”

“…For example, harvesting was conducted at the L5 stage [102] when the first prepupae were found [103], or at 10-100% prepupae formation [82,84,104], or at the pupae stage [105]. However, other studies predefine a harvest date that could range between 8 d [80] to 20 d [89] or allow the prepupae to self-harvest by actively crawling out of the substrate [24,96]. The emerged flies are not fed in the conventional sense but are commonly offered water to drink.…”

Optimizing Substrate Moisture Content for Enhanced Larval Survival and Growth Performance in Hermetia illucens: Exploring Novel Approaches

“…In this study the in uence of the substrate moisture content on BSFL rearing is investigated. The moisture content of the substrate is pivotal as larval performance, e.g., growth, bioconversion e ciency, waste reduction and survival, is highly affected by the substrate moisture content (Bekker et Yakti et al, 2023). Understanding the in uence of substrate moisture content on the rearing process is therefore crucial for the optimization of BSFL rearing.…”

“…Understanding the in uence of substrate moisture content on the rearing process is therefore crucial for the optimization of BSFL rearing. Studies have shown that substrate moisture content is positively correlated to larval growth, however when substrate moisture contents are too high, survival drop signi cantly, often leading to inconsistencies in yield per box [17][18][19][20].…”