4.22 Black Soldier Fly Larvae Frass Production, by Crop, Zimbabwe

are based on 100 percent recovery of crop wastes for substrate use. Actual protein totals will scale down according to the recovery level achievable for each crop substrate. Scaling is linear, meaning that if the overall recovery rate is 50 percent and all of that is used as substrate, then the resultant available crude protein will fall by 50 percent. For example, in table 4.20, the theoretical value (100 percent waste recovery) of total crude protein produced is 116,502 tons, assuming a 30 percent waste conversion factor. However, if only 50 percent of wastes are recovered and used as substrate, the resultant crude protein will be 50 percent of 116,502 tons, or 58,251 tons of crude protein, which would cover 8.5 percent of total protein demand (see table 4.20).

Frass for Biofertilizer

BSFL produces an abundant amount of high-quality biofertilizer, which is the BSFL’s excrement (frass), mixed with the spent substrate. The amount of frass produced by BSFL from the various crop substrates is summarized in table 4.22. An individual insect larva can consume between 25 and 500 milligrams of organic matter per day depending on the larva’s size, the type of substrate available, and the feeding conditions, which include air supply, temperature, and moisture levels (Makkar et al. 2014). Through the feeding process, BSFL release the substrate’s nitrogen, phosphorus, and potassium (NPK). As such, the frass contains essential elements for plant growth and is used as

TABLE 4.22 Black Soldier Fly Larvae Frass Production, by Crop,

Zimbabwe

Crop Residue (tons) Postharvest loss (tons) Process waste (tons) Consumption waste (tons) Total (tons)

10% conversion

30% conversion

maize 65,678 11,475 2,960 324 80,437 groundnut 18,131 763 1,645 — 20,539 soybean 6,395 322 91 — 6,808 sugarcane 54,273 3,618 115,700 — 173,591 wheat 3,187 598 360 25 4,170

Total 147,664 16,777 120,756 349 285,545

maize 197,033 34,425 8,881 971 241,310 groundnut 54,393 2,290 4,935 — 61,618 soybean 19,184 967 273 — 20,424 sugarcane 162,820 10,855 347,099 — 520,774 wheat 9,562 1,793 1,079 74 12,509

Total 442,992 50,330 362,267 1,046 856,635

Source: Original table for this publication. Note: — = not available.