In Africa, livestock production currently accounts for about 30% of the gross value of agricultural production. However, production is struggling to keep up with the demands of expanding human populations, the rise in urbanization and the associated shifts in diet habits. High costs of feed prevent the livestock sector from thriving and to meet the rising demand. Insects have been identified as potential alternatives to the conventionally used protein sources in livestock feed due to their rich nutrients content and the fact that they can be reared on organic side streams. Substrates derived from organic by-products are suitable for industrial large-scale production of insect meal. Thus, a holistic comparison of the nutritive value of Black Soldier Fly larvae (BSFL) reared on three different organic substrates, i.e. chicken manure (CM), brewers’ spent grain (SG) and kitchen waste (KW), was conducted. BSFL samples reared on every substrate were collected for chemical analysis after the feeding process. Five-hundred (500) neonatal BSFL were placed in 23 × 15 cm metallic trays on the respective substrates for a period of 3–4 weeks at 28 ± 2 °C and 65 ± 5% relative humidity .
The larvae were harvested when the prepupal stage was reached using a 5 mm mesh size sieve. A sample of 200 grams prepupae was taken from each replicate and pooled for every substrate and then frozen at −20 °C for chemical analysis. Samples of BSFL and substrates were analyzed for dry matter (DM), crude protein (CP), ether extracts (EE), ash, acid detergent fibre (ADF), neutral detergent fibre (NDF), amino acids (AA), fatty acids (FA), vitamins, flavonoids, minerals and aflatoxins. The data were then subjected to analysis of variance (ANOVA) using general linear model procedure. BSFL differed in terms of nutrient composition depending on the organic substrates they were reared on. CP, EE, minerals, amino acids, ADF and NDF but not vitamins were affected by the different rearing substrates. BSFL fed on different substrates exhibited different accumulation patterns of minerals, with CM resulting in the largest turnover of minerals. Low concentrations of heavy metals (cadmium and lead) were detected in the BSFL, but no traces of aflatoxins were found. In conclusion, it is possible to take advantage of the readily available organic waste streams in Kenya to produce nutrient-rich BSFL-derived feed.
The global food demand is expected to increase by 70% by the year 2050 in order to meet the demands of the 9.7 billion people who are forecasted to inhibit the globe by that time. In the recent past already major shifts in diets have happened, favoring more animal-based foods, in particular milk, meat, fish and eggs, and these preferences are expected to increase with time. These changes in dietarian pattern have been accelerated by economic growth, coupled with rapid migration from rural to urban areas, as well an increasing awareness in nutritional needs. By the middle of the current century, cereal and meat production are expected to increase from 2.1 billion and 258 million tons produced per annum between 2005 and 2007 to 3.0 billion and455 million tons, respectively, raising worldwide concerns regarding the status of food security.
In the developing world, the livestock sector can act as a gateway towards alleviating poverty and enhancing food security. Kenyan poultry farming is a significant source of income, especially in rural areas, and contributes to more than quarter of the agricultural Gross Domestic Product (GDP) and accounts for 8% of the total GDP in Kenya. Yet feed costs make up more than 70% of the production costs, highlighting the important role economic feeds and their availability could play in successful poultry farming.
Due to food-feed competition, feed constituents that are suitable for direct human consumption such as soybean and fish are expensive and collectively increase the costs of feeds. In addition, global catches from the marine fish stocks have dwindled over the years due to overexploitation. This increases the price of fishmeal, which is not only used in feeding livestock but rather is a major source of protein in farmed fish feed. Moreover, the intensification of soybean production, especially in the tropics, resulted in land grabbing and deforestation in addition to other negative social and environmental consequences. For the reasons mentioned above, there is an urgent need to replace conventional feed ingredients such as soybean and fish with innovative, economically beneficial and environmentally sustainable ones.
Large-scale rearing of insects is a promising and innovative alternative as several insects’ species can feed of various types of organic waste streams. In addition, insects are precious reservoirs of proteins, fatty acids, micronutrients and contain high amounts of energy. The latter show a good profile of amino acids in general, and of the most-limiting essential ones like lysine, threonine and methionine, often lacking in plant-based protein sources for non-ruminants.
The Black Soldier Fly (BSF) Hermetia illucens L. (Diptera: Stratiomyidae), the common house fly Musca domestica L. (Diptera: Muscidae) and the yellow mealworm Tenebrio molitor L. (Coleoptera: Tenebrionidae) are among the insect species that have been recognized as promising alternative sources of protein for animal feed. The first two naturally occur in animal droppings but also flourish on other organic waste substrates such as coffee bean pulp, vegetables residues, catering waste, municipal organic waste, straw, dried distillers grains with solubles (DDGS), and fish offal15, and can add value by reducing organic waste biomass by 50–60% and turning them into high protein biomass. The yellow mealworm can be reared on vegetables and DDGS. The dry weight of Black Soldier Fly larvae (BSFL) contain up to 50% crude protein(CP), up to 35% lipids and have an amino acid profile that is similar to that of fishmeal. They are recognized and utilized as alternative sources of protein for feed of poultry, pigs, and several species of fish and shrimp.
The adult fly can typically live for one to two weeks without the need to feed as it appears it can rely on fat body reserve that was acquired during larval stages and can even live longer when fed with water. It does not carry diseases, and actively feeding BSFL secrete an info-chemical that keeps away other species of flies, thereby repelling potential insect pests and disease vectors such as M. domestica. The same authors also reported that BSFL significantly influence the reduction of Escherichia coli and Salmonella enterica presence in cow dung while Liu and colleagues reported the same influence on Escherichia coli in chicken manure. The economic feasibility of the use of insects as feed largely depends on cost effective and readily available organic waste streams, both in the developed and in particular in the developing world. So far, very few studies assessed the holistic nutritional contents of BSFL in terms of quality using experimental diets that were established within the means of the developing world. Unlike rationed diets, organic waste streams in the developing world are heterogeneous in nutritional composition and might be an environment where heavy metals can accumulate.
Therefore, the current study sought to perform a comparative holistic analysis of the quality of the nutritional composition of BSFL reared on organic waste streams that are largely and readily available in urban areas of Kenya and the developing world in general. A comparative study that is essential when deciding which organic waste streams are potentially suitable for industrial large-scale BSFL production in Kenya.
The family Stratiomyidae comprises 260 known species in North America (Triplehorn 2005). In the southeastern United States, the black soldier fly is abundant during late spring and early fall and has three generations per year in Georgia (Tomberlin et al. 2002). While common in the continental United States, this fly is found throughout the Western Hemisphere.
In natural breeding sites (i.e. carrion) black soldier flies lay their eggs in moist organic material. Black soldier flies frequent agricultural settings because the large amounts of the organic waste left by livestock offer abundant sites that meet their reproductive needs. In areas where natural habitats are removed (urbanized areas) the black soldier fly will lay eggs in dumpsters or compost, which provide similar odors and nutritional needs to naturally occurring organic matter. This is especially true for areas with poor sanitation.
The adult black soldier fly is not usually considered a pest (Newton et al. 2005). Because the larvae have been shown to be effective manure recyclers, a "Black Soldier Fly Manure Management System" has been proposed to not only reduce livestock waste, but also generate a food source for fish and other animals. In a program outlined in Newton et al. (2005) swine manure was fed to black soldier fly larvae, which greatly reduced the waste material. The manure was transferred into a basin containing black soldier fly larvae. As the larvae developed they reduced the manure by 50%. Approximately 45,000 larvae will consume 24 kg of swine manure in 14 days. As the larvae mature they crawl out of the basin, thereby self-harvesting themselves, and are subsequently available as livestock feed. In addition to being a good source of oil and protein for animal feed, black soldier fly larvae have the potential of improving organic waste into a rich fertilizer.
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