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
30% conversion
10% conversion
TABLE 4.22 Black Soldier Fly Larvae Frass Production, by Crop, Zimbabwe Crop
Residue (tons)
Maize
65,678
11,475
2,960
324
80,437
Groundnut
18,131
763
1,645
—
20,539
Soybean Sugarcane Wheat
PostProcess harvest waste loss (tons) (tons)
Consumption Total waste (tons) (tons)
6,395
322
91
—
6,808
54,273
3,618
115,700
—
173,591
3,187
598
360
Total
147,664
16,777
120,756
349
285,545
Maize
197,033
34,425
8,881
971
241,310
54,393
2,290
4,935
—
61,618
Groundnut Soybean Sugarcane Wheat Total
25
4,170
19,184
967
273
—
20,424
162,820
10,855
347,099
—
520,774
9,562
1,793
1,079
442,992
50,330
362,267
74 1,046
12,509 856,635
Source: Original table for this publication. Note: — = not available.
Mainstreaming Insect Farming
161