4.7 BSF-Related Conversion Factors

protein derived from the dry meal8 against the protein requirements of certain livestock: pigs, goats, chickens, and fish from aquaculture.

The model was extended beyond Zimbabwe to analyze Africa as a whole and 10 additional African countries individually. The analysis for all of Africa included the same five crops studied in Zimbabwe—maize, wheat, soybean, groundnut, and sugarcane—to determine the potential production volume of BSFL and frass and the impact of each. The assessment of individual African countries included the 10 countries with the largest agricultural economies on the continent. These are, from largest to 10th largest, Nigeria, Kenya, the Arab Republic of Egypt, Ethiopia, Algeria, Tanzania, Morocco, Sudan, Ghana, and Angola. The analysis added cassava to the list of crops to reflect the agriculture sector in the 10 countries, although the analysis for each country was limited to only five of the six crops—the five with the highest production tonnage for each country (annex 4A provides details of the analysis and the full results).

Achieving maximum conversion rates depends on how substrates are prepared. Crop residues, for example, may be fibrous and may not be fully consumed by BSFL. Therefore, grinding and fermenting fibrous materials before feeding them to BSFL allows the BSFL to consume them more completely, thus raising the substrate-to-BSFL conversion. Considering that BSF breeding is a nascent industry, more studies are required to establish best practices for crop waste preparation, determine crop-specific conversion rate estimates, and estimate more accurately BSFL’s final frass and crude protein outputs.

Other wastes can be used as BSFL substrates but are not included in the model. These substrates include crops other than the five used in the modeling, including various types of processing waste. For example, rotten vegetables are ideal for BSFL consumption and can be collected from vegetable processing plants. Brewer spent grains (BSG) are another potential substrate for BSFL. BSG are an excellent source of crude protein for livestock and are in high demand for that reason. It is more efficient to feed BSG directly to livestock than to convert them to protein through BSFL. However, the shelf life of BSG is only a day or two at ambient temperatures or two or three days if kept refrigerated. Spoiled BSG should not be fed to livestock, but the

TABLE 4.7 BSF-Related Conversion Factors

BSFL to dry meal Meal crude protein content All other conversion factorsa Low High

34% 40% 10% 30%

Source: Original table for this publication, using J. K. Tomberlin, personal communication. Note: BSF = black soldier fly; BSFL = black soldier fly larvae. a. Conversions of all croprelated wastes to BSFL and all croprelated wastes to frass.

bioremediation ability of BSFL makes spoiled BSG an ideal BSFL substrate. In short, fresh BSG are ideal for livestock, but spoiled BSG are ideal for BSFL. BSFL can also feed on animal and human waste, as discussed in the previous section, but manure and human fecal waste are not considered substrates in the model because they can potentially introduce heavy metals, salmonella, or other pathogens.

These modeled projections are not realistic in the short term for several reasons. First, initially, few farmers are likely to participate in BSF breeding. As a result, BSFL production will be limited until the sector gains wider traction. Second, it will take time to educate farmers on the benefits and techniques of BSF breeding. Farmers can learn the industry from other farmers or from technical agricultural extensionists, but this will require time. Third, BSF farms will require labor, which may be hard to attain before farms reach scale and can pay consistent wages. Fourth, crop wastes can be used for other purposes in addition to BSF breeding, so even if 100 percent of crop wastes were recovered, it would be unlikely that all of it would be used as BSFL substrate. To determine whether a particular crop residue serves better as BSFL substrate or something else would require a cost-benefit analysis.

Maize

Figure 4.10 shows the food supply chain and associated waste stream for maize in Zimbabwe. The following analysis determines BSFL meal and frass production based on the five-year (2013–17) averages for total annual maize production (735,560 tons9) and harvested area (1,133,690 hectares (ha)). The numbered bullets below show the kilogram per hectare calculations for each type of maize-associated waste. These are then multiplied by the total area under cultivation (hectares) and divided by 1,000 (kg/ton) to determine the total tons per hectare per waste type. Table 4.8 summarizes the total maize-derived wastes recoverable and suitable as substrates for BSF breeding. Table 4.9 applies the 10 and 30 percent conversion rates to the wastes in table 4.8 to calculate the rate of converting maize wastes to BSFL meal and frass for biofertilizer.

1. Based on the five-year average of maize production and area planted, the average maize yield is 651 kg/ha and the associated crop residue, or stover, amounts to 579 kg/ha. Stover and some other crop residues are used for various purposes. For example, a study of 310 western Kenyan farms showed that 47 percent of crop residue remains on the fields as an organic soil amendment, 25 percent is fed to livestock, 22 percent is used as cooking fuel, and the remaining 6 percent is used for miscellaneous purposes (Berazneva 2013).10 Residues are also often burned in the field in Sub-

Saharan Africa. The residues can be a clean, abundant, readily available, and essentially no-cost substrate for BSFL.