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Efforts to recycle organic wastes using black soldier fly (BSF) Hermetia illucens into high-nutrient biomass that constitutes a sustainable fat (biodiesel) and high-quality protein ingredient in animal feeds have recently gained momentum worldwide. However, there is little information on the most suitable rearing conditions for growth, development and survivorship of these flies, which is a prerequisite for mass production technologies. We evaluated the physiological requirements for growth and reproduction of H. illucens on two diets [spent grains supplemented with brewers' yeast (D1) and un-supplemented (D2)]. Development rates at nine constant temperatures (10-42°C) were fitted to temperature-dependent linear and non-linear day-degree models. Thereafter, life history table parameters were determined within a range of favourable temperatures. The thermal maximum (TM) estimates for larval, pre-pupal and pupal development using non-linear model ranged between 37.2 ± 0.3 and 44.0 ± 2.3°C. The non-linear and linear day-degree model estimations of lower developmental temperature threshold for larvae were 11.7 ± 0.9 and 12.3 ± 1.4°C for D1, and 10.4 ± 1.7 and 11.7 ± 3.0°C for D2, respectively. The estimated thermal constant of immature life stages development of BSF was higher for the larval stage (250±25 DD for D1 and 333±51 for D2) than the other stages evaluated. Final larval wet weight was higher on D1 compared to D2. The population growth rate was most favourable at 30-degree celsius (°C) with higher intrinsic rate of natural increase (rm = 0.127 for D1 and 0.122 for D2) and shorter doubling time (5.5 days for D1 and 5.7 days for D2) compared to the other temperatures. These results are valuable for the optimization of commercial mass rearing procedures of BSF under various environmental conditions and prediction of population dynamics patterns using computer simulation models.

Current trends predict a global population increase to about 10 billion people by 2050, forcing an increased food or feed production, which exerts pressure on the environment for resources. With the increasing human population, increased urbanization and income rise, there is an increased demand for animal-based foods such as beef, dairy, pork, chicken, eggs and fish. Efficient animal production requires adequate feeding to produce high-quality animal products. Aquaculture and livestock industries face challenges related to the availability of sustainable and affordable feed ingredients. Fishmeal (FM) and soybean meal are the major protein sources in animal feed, which are increasingly becoming scarce and unaffordable, thereby increasing the total cost of production. High costs of production adversely affect growth of production and livelihood of smallholder producers, particularly in developing countries. Currently, interest in using insects as an alternative nutrient source is growing and the need to establish an insect sector has become important, but for insect-based feed to make a substantial contribution in substituting the conventional protein-rich FM and soybean meal, large quantities of insect biomass are required, which makes insect mass rearing an inevitable step. Knowledge on sources of substrates for rearing insects, suitability of insect meal as feed ingredient, as well as acceptance and demand by end users is therefore important for a sustainable insect-based feed sector. The study described in this thesis focused on the potential of black soldier fly (BSF) larvae as a feed ingredient and farmers’ willingness to pay (WTP) for insect-based feed in Kenya.Chapter 2 presents an overview of the current literature on the potential of insects as an alternative animal feed ingredient and the role insect farming can play in inclusive business models for smallholder farmers, with a focus on the BSF. Insects are highly nutritious, with protein contents comparable to FM and soybean meal. The BSF is the most suitable insect species reared for animal feed because it is not considered as a pest or vector of diseases and can its larvae exploit a wide range of food substrates, including organic side streams such as manure. The larvae can upgrade low value organic side streams to a high-quality feed ingredient. Moreover, insect farming fits well into the concept of a circular economy and has great prospects for animal feed and waste management, with valuable consequences for many societal aspects, which align with various Sustainable Development Goals, including reduction of poverty, hunger and food waste.In Chapter 3, farmers’ knowledge of and attitude towards insects as feed, and their WTP for insect-based feed were assessed using a contingent valuation method. We found that poultry and fish farmers are aware that insects can be used as a feed ingredient. Famers have a positive attitude that insects are a nutritious feed ingredient for animals. Furthermore, farmers are willing to pay for insect-based feed. In addition, factors such as age of farmer, gender, education level, marital status, distance to feed trader, awareness of insects as feed, attitude towards insects as feed, acceptance of insect species, availability of agricultural inputs, training, and market information affect farmers’ WTP for insect-based feed. These findings imply that there is a potential demand for insect- based feed in Kenya and suggest that the implementation of extension programmmes to educate famers on the nutritional value of insects as well as provide market information may improve farmers attitude towards insects, create more awareness and enhance WTP for insect-based feed. Our findings also highlight the need for increased training programmes towards capacity building of local insect producers in order to increase local production and availability of insects for the animal feed value chain, which is currently recognized by the Kenyan government.Availability and accessibility of suitable substrates is key to a successful insect mass rearing operation. In Chapter 4, we explored the potential of rearing BSF larvae on a combination of agro-industrial by-products composed of brewers’ spent grains (BSG) and brewer’s yeast from beer brewing, and molasses from cane sugar production. Immature and adult life history parameters including: larval development, survival, adult emergence, adult longevity and fecundity of the BSF were assessed. Our results show that BSF larvae successfully developed to pre-pupae in all substrate combinations, with 86-99% larval survival. When provided with water or a sugar solution upon emergence, adult BSF lived 2-3 times longer than adults BSF that were not fed. Unfed female BSF died without ovipositing, whereas the water- or sugar- female BSF successfully oviposited. These findings imply that the BSG are a suitable substrate for rearing BSF larvae. Supplementing BSG with brewer’s yeast or a combination of brewer’s yeast and molasses supports larval growth and, therefore, is a valuable strategy to manage brewer’s yeast and cane molasses. These findings are valuable in the production of BSF larvae as feed as well as in the management of organic waste streams through bioconversion of substrates. The results also provide insight into the management of adult BSF colonies to achieve optimal performance.The time taken for most insects to complete a specified growth stage is largely dependent on temperature and food. In Chapter 5, BSF larvae were reared on BSG supplemented with brewer’s yeast or un-supplemented at nine constant temperatures. Our results show that supplementing BSG with brewer’s yeast resulted in higher weight of BSF larvae compared to the un-supplemented substrates. Furthermore, the population growth rate of BSF was most favourable at 30 ˚C with a higher intrinsic rate of natural increase and shorter doubling time compared to the other temperatures evaluated. These findings are valuable for the optimization of rearing conditions of the BSF under various environmental conditions and the prediction of population dynamics.The BSF larvae convert organic material into high-quality insect biomass that can be used as a feed ingredient. The nutrient composition of the larvae may vary depending on the substrates on which the larvae are reared. In Chapter 6, we therefore assessed the nutritional quality of BSF larvae reared on agro-industrial by-products composed of BSG, brewer’s yeast and molasses (Chapter 4) for animal feed. Our results show that larvae reared on all the substrates investigated were rich in protein, with a balanced amino acid profile, fats, predominated by saturated fatty acids, as well as macro- and micro- minerals. Furthermore, supplementing BSG with brewer’s yeast resulted in higher crude protein content of the BSF larvae than obtained on substrates without brewer’s yeast. The BSF larvae contained 30-46% crude protein, which is comparable to values recorded for BSF larvae reared on other substrates such as fruit and vegetable wastes in other studies. These findings imply that BSF larvae reared on these agro-industrial by-products are nutritionally suitable for animal feed.FM is the major source of protein in animal feed, but its rapidly reducing availability leads to increased prices. Alternative sources of protein are therefore needed for animal feed production. The BSF larvae are a novel protein source widely used in aquaculture and poultry feeds, but little is known about the effect of substituting FM with black soldier fly larval meal (BSFLM) on growing and finishing pigs. In Chapters 7 and 8, the potential of a partial or complete replacement of FM by BSFLM on growth and economic performance, carcass yield and nutritional quality of pigs was investigated. Pigs were fed different diet types: control (no BSFLM: 0%), 25, 50, 75 and 100% replacement of FM by BSFLM for the grower and finisher phases of the pigs. Our results show that the replacement of FM by BSFLM did not affect feed intake, daily weight gain, red or white blood cell counts as wells as serum lipid indices of pigs in the grower phase (Chapter 7). Moreover, the inclusion of BSFLM in feed for growing pigs did not affect the value of return on investment (RoI) estimated, but the cost benefit ratio showed a value greater than 1.0, which means that BSFLM can be considered as an ingredient in commercial production of pig feed.In the finishing phase (Chapter 8), the inclusion of BSFLM greatly improved feed conversion and daily weight gain of the pigs. Replacing FM with 50-100% levels of inclusion of BSFLM in feed led to higher carcass weights than at lower levels of BSFLM. Furthermore, pork tissues were rich in crude protein and minerals across all diet types tested. BSFLM proves to be a suitable ingredient in finishing pig feed and can completely replace FM with beneficial consequences for growth, carcass and nutritional quality of edible pork by-products. These findings are valuable for the production of insect-based feed for pigs. In Chapter 9, the key findings of this research and the implications for BSF production in Kenya are addressed and recommendations for future investigations are provided. In conclusion, the results of the research described in this thesis show that farmers are aware that insects can be used as a feed component and are willing to pay for insect- based feed in Kenya. The combination of agro-industrial by-products, composed of BSG, brewer’s yeast and molasses is suitable for rearing BSF larvae. Moreover, the addition of brewer’s yeast to BSG leads to higher protein content of the BSF larvae. Furthermore, the inclusion of BSFLM in pig feed improves pig growth and carcass quality. Farmer sensitization on the nutritional value of the different insect species, especially the BSF is necessary to increase awareness and enhance WTP for insect-based feed among farmers. Organoleptic studies are recommended on