How are Black Soldier Fly Larvae responding to the inclusion of glucose to the feed?

By Hochschule Bremerhaven

The objective of this pilot trial was to determine the tolerance level of pure glucose in feed for Black Soldier Fly Larvae (BSFL). The results from the tolerance test will provide information on how large the glucose fraction can be when mixing cellulose from lignocellulosic biomass with municipal solid waste.

The trial ran for 5 days in March 2023 mixing glucose with standard ENORM feed at different inclusion levels. In order to mix the glucose with the feed, a glaze consisting of 80% glucose and 20% water was made. The glaze and standard operation procedure (SOP) feed was mixed based on weight for a total weight of 500 g. The inclusion levels of the glaze were 0 (control), 10, 20, 30, 40 and 50% equivalent to 0, 8, 16, 24, 32 and 40% pure glucose mixed with the SOP feed. Feed and glaze were mixed until a homogenous mixture was reached. Further, the feed was dosed in small containers and 722 seed-larvae (5 days old larvae) were added to each container; seed-larvae were dosed based on weight. The containers were placed in the standard 60×40 cm growth crate and placed in a stable SOP climate for growth-larvae.

The containers were harvested after 5 days. However, the tests with inclusion levels of 30% glaze and above were excluded as the substrate in the containers had a consistency similar to caramel which did not make it possible to separate the larvae from the substrate. It was also observed that the larvae were very small and especially tests with 40 and 50% glaze saw a high mortality rate which could be due to substrate providing limited mobility. The control together with 10 and 20% glaze tests were harvested but not without struggle as the larvae in general were small and the frass particles quite large compared to the main production line at ENORM. The low weight of the larvae is also reflected in the larvae-biomass yield which decreased with higher inclusion of glaze. However, all three tests saw a +100% survival rate which is possible as the seed-larvae were dosed based on weight and not precise number. The results suggest, that the feed conversion ratio (FCR) is not only affected by the low biomass yield but also the increasing dry matter content of the feed which increased with higher inclusion of glaze. For comparison, the standard weight of larvae is approximately 0.180-0.200 g, while the FCR is 1.3.

Key results:

Based on the objectives of the trial, it can be concluded that up to 16% of the feed can consist of glucose without affecting the survival rate of the larvae but increasing glucose levels is expected to result in lower biomass yield.
The results for the control could indicate that the tests were affected by different variables which could explain the high FCR.