BSF production: predictable like weather

In various research studies (like those by Lalander et al. in 2019 and Liew et al. in 2022), scientists have found a clear connection between certain input factors (such as the concentration of P+C, volatile solids, and soluble chemical oxygen demand) and the output factor of larval yield.

Recently, M. KieBling and their team (2023) have used a simple mathematical model called linear regression (shown in Equation 2) to understand how macronutrients affect the weight of prepupae (young insects). They looked at different aspects, including the direct influence of nutrients like crude lipid and protein, the squared effect of these nutrients, and how they interact with each other.

Interestingly, they didn’t consider the amount of digestible carbohydrates in their model because their experiments showed that having more than 20% of these carbohydrates was enough for the growth of Black Soldier Fly (BSF) larvae, as suggested by Cammack and Tomberlin in 2017. This means carbohydrates weren’t a limiting factor in larval growth in their study.

𝑃𝑟𝑒𝑝𝑢𝑝𝑎𝑒 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑚𝑔)=𝑏𝑜+𝑏1∗𝐶𝑟𝑢𝑑𝑒 𝑙𝑖𝑝𝑖𝑑 (% 𝑑𝑚)+𝑏2∗𝐶𝑟𝑢𝑑𝑒 𝑝𝑟𝑜𝑡𝑒𝑖𝑛 (% 𝑑𝑚)+𝑏3∗𝐶𝑟𝑢𝑑𝑒 𝑙𝑖𝑝𝑖𝑑2+𝑏4∗𝐶𝑟𝑢𝑑𝑒 𝑝𝑟𝑜𝑡𝑒𝑖𝑛2+𝑏5∗𝐶𝑟𝑢𝑑𝑒 𝑙𝑖𝑝𝑖𝑑∗𝐶𝑟𝑢𝑑𝑒 𝑝𝑟𝑜𝑡𝑒𝑖𝑛 (2)

This model does a pretty good job of fitting the data, capturing about 86% of the information. Let’s break down the coefficients: We have -45.6 (bo), 34.57 (b1, indicating a positive linear effect), 2.171 (b2, another positive linear effect), and -1.523 (b3, a negative quadratic effect), as well as a couple of “not significant” values (b4 & b5, which means they didn’t have much impact).

In simpler terms, it means that the amount of crude protein (b2) in the food (which can vary from 7.9% to 47.5%) has a fairly straightforward impact on how much the larvae weigh. More protein generally means heavier larvae. But when it comes to crude lipid content, things get a bit trickier (b1 & b3) . The larvae’s weight doesn’t just go up with more lipids; it actually has a U-shaped relationship. They do best at around 10% crude lipid content.

This model was built using 54 different food types, and they made sure that all the other conditions, like larval density, environment, and food handling, were the same. This way, the data is consistent and reliable.

Now, if you know what’s in the food, you can use this model to predict how much the prepupae will weigh when they’re 17 days old.

Figure 1. Estimated Diagram for predication model

But that’s not all – there’s potential for more in the future. In a study by Lalander and their team in 2019, they found that there’s a strong link between the rate at which insects break down organic materials called volatile solids (VS) and the final weight of prepupae. And another concept called chemical oxygen demand (COD) can help estimate how much energy is in the larvae’s diet. You can explore the relationship between COD and larval weight further.

Check out the diagram below (Fig. 1) to see how all these factors might come together to predict BSF larva production. This model looks at the connection between the prepupae’s average weight and how much food they consume in terms of VS, COD, and energy. It’s an exciting path for future research!

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