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Journal of Insects as Food and Feed, 2016; 1(1): 1-13 Wageningen Academic
Publishers
ISSN 2352-4588 online, DOI 10.3920/JIFF2018.0017 1
1. Introduction
In the developing countries, rapid urbanisation coupled
with changes in demographics and consumer behaviour,
has resulted in new challenges in solid waste management
(Diener et al., 2011b). In these countries, organic waste
accounts for 80% of the total municipal waste and is often
looked upon as a waste fraction without market value and
therefore ignored by the waste recycling sector. In Kenyan
urban slums, for example, faecal waste disposal is mainly
through open pit latrines, bucket latrines, hanging latrines
and even polythene papers. The latter are often thrown
into the streets and nearby rivers in the wee hours of the
morning, a practice commonly known as ‘flying toilets’ in
An optimal feeding strategy for black soldier fly larvae biomass production and faecal
sludge reduction
E.M. Nyakeri1,2*, M.A. Ayieko1,2, F.A. Amimo3, H. Salum4 and H.J.O. Ogola5
1
School of Agricultural and Food Sciences, Jaramogi Oginga Odinga University of Science and Technology, P.O. Box 210,
40601 Bondo, Kenya; 2Africa Centre of Excellence in Sustainable Use of Insects as Food and Feeds (ACE-INSEFOODS),
Jaramogi Oginga Odinga University of Science and Technology, P.O. Box 210, 40601 Bondo, Kenya;
3
School of Health
Sciences, Jaramogi Oginga Odinga University of Science and Technology, P.O. Box 210, 40601 Bondo, Kenya;
4
School of
Biological Sciences, University of Dodoma, P.O. Box 320, Dodoma, Tanzania; 5Department of Environmental Sciences,
College of Agriculture and Environmental Science, University of South Africa, P.O. Box 392, Florida 1710, South Africa;
evans.nyakeri@gmail.com
Received: 7 March 2018 / Accepted: 29 January 2019
© 2019 Wageningen Academic Publishers
RESEARCH ARTICLE
Abstract
The dual roles of efficient degradation and bioconversion of a wide range of organic wastes into valuable animal
protein and organic fertiliser, has led to increased interest in black soldier fly (BSF) technology as a highly promising
tool for sustainable waste management and alternative protein production. The current study investigated the
potential application of BSF technology in the valorisation of faecal sludge (FS), a common organic waste in the
urban informal settlements in low and middle-income countries. We evaluated the effect of different feeding rates
(100, 150, 200 and 250 mg/larva/day), different feeding regimen and supplementation with other waste feedstock
(food remains, FR; brewers waste, BW; and banana peelings, BP) on BSF larvae (BSFL) growth rates/yield and
FS reduction efficiency. Results showed significantly (P<0.01) higher prepupal yield (179±3.3 and 190±1.2 g) and
shorter larval development time (16.7 and 15 days) when reared on 200 and 250 mg/larva/day FS, respectively.
However, different feeding regimes of FS did not significantly affect larval growth rate and prepupal yield (P=0.56).
Supplementation of FS with other organic substrates resulted in significantly increased BSFL biomass production
and substrate reduction, and shortened larval development time; with the effect was more pronounced when FS
was supplemented with FR and at 30% supplementation. Protein:fat ratios for BSFL reared on FS, FS:FR, FS:BW
were significantly (P<0.05) higher (2.51, 2.53, and 2.44, respectively) compared to FS:BP mixture (1.99). These
results demonstrated that supplementation of FS with locally available organic waste can be used to improve its
suitability as feedstock for BSF production and organic waste bioremediation from the environment. In conclusion,
a daily feeding strategy of substrate containing FS supplemented with 30% organic waste co-substrate at feeding
rate of 200 mg/larva/day can be used as a guideline for BSFL mass production and bioremediation of FS both at
small- and large-scale level.
Keywords: bioremediation, waste supplementation, feeding regime, BSF technology, prepupae, substrate reduction
Journal of Insects as Food and Feed, 2019 online ARTICLE IN PRESS
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E.M. Nyakeri et al.
2 Journal of Insects as Food and Feed ##(##)
local lingua franca. The endemic lack of sanitation in these
habitats is attributed to many but related factors such as
high cost of emptying the open pit latrines once filled, lack
of land to dig new pit latrines, high population density and
inability of most local governments to provide sewer lines
(Diener et al., 2011b; Guerrero et al., 2013). The need to
add value to the management of organic waste including
faecal sludge (FS) and enable the process meet its own costs
has inspired the search for new and financially attractive
disposal methods.
Black soldier fly (BSF; Hermetia illucens L.; Diptera:
Stratiomyidae), a tropical fly that inhabits tropical and
warm-temperature regions worldwide, is known to feed on
a wide range of many biological wastes. Upon hatching from
eggs, BSF larvae uses surrounding organic matter as a food
source. The growing larvae undergoes successive moulting
across five instar stages whose duration can last between
2 weeks and 6 months depending on food availability and
environmental conditions), before becoming pupae (12-25
mm long), an imago and then metamorphosize into adult
fly (Tomberlin et al., 2009). The prepupa form takes 2-3
weeks to complete the prepupal stage before moulting into
pupa that are black in colour (Caruso et al., 2014).
BSF larva (BSFL) is generally characterised by the ability to
colonise a wide variety of resources due to a robust digestive
system, a ferocious appetite and capacity to transform
large quantities of organic waste (from 25 to 500 mg of
fresh matter per larva per day) into biomass (Bondari and
Sheppard, 1987). This organic waste conversion rate is more
than any other known fly species. The ability of BSFL to
valorise and transform organic wastes into highly valuable
biomass and organic fertiliser is considered a promising
technology in waste disposal (Cammack and Tomberlin,
2017), and as a means of reducing the amount of residues
destined for landfilling and incineration (Barry, 2004).
For example, waste reduction of 65.5-78.9% of municipal
organic waste have been reported in Costa Rica (Diener
et al., 2011a). Application of BSF technology in manure-
management system (Newton et al., 2005; Sheppard et
al., 1994) and food wastes (Hem et al., 2008; Nyakeri et
al., 2017; St Hilaire et al., 2007), with waste reduction
above 50%, have also been demonstrated. Other benefits
associated with BSF include use of the generated larval
biomass as a protein and fat source for domestic animals
feed, production of biodiesel, utilisation of chitin and its
derivatives in medical, pharmaceutical applications, food
processing, packaging of cosmetics, textiles and agriculture
(Bondari and Sheppard, 1987; St Hilaire et al., 2007; Wang
and Shelomi, 2017; Zheng et al., 2013), and as biocontrol
agent of pest flies and pathogens (Bradley and Sheppard,
1984; Liu et al., 2008). BSFL, estimated worth $ 2.32/kg
(Bullock et al., 2013), can be used to greatly reduce the costs
of animal feed, which amount to 60-70% of total operational
costs, and may viably contribute to the economics of organic
waste treatment (Arango Gutiérrez et al., 2004; Barry,
2004; Newton et al., 2005; Norhidayah, 2016; Wang and
Shelomi, 2017). Therefore, combination of waste treatment
capacity together with generation of a valuable product
makes the BSF technology a highly promising tool for waste
management in low and middle-income countries (Diener
et al., 2011a).
Although BSF develops naturally on organic material,
larvae and adults become inactive under sub-optimal
environmental and feeding conditions. Generally, there is
limited information on BSF rearing, but few studies have
identified knowledge gaps related to biological larvae
requirements (Banks et al., 2014; Brits, 2017; Diener
et al., 2009, 2011a; Nyakeri et al., 2017; Oonincx et al.,
2015a,b). Previously, we reported the potential utilisation
of BSF composting in valorisation and bioremediation
of local organic wastes including faecal matter from the
environment (Nyakeri et al., 2016, 2017). In these studies,
BSFL production and waste reduction efficiency, and
nutritional profiles were dependent on the waste type
and environmental conditions regimen. However, low
productivity was achieved on specific organic substrates,
such as FS and banana peelings (BP) waste, even though
BSFL are known to consume a wide range of materials from
plant, animal and industrial wastes. For sustainability, there
is need to develop an efficient BSFL rearing systems for the
biomass production and utilisation in waste management.
High mortality rates observed coupled with slow growth
rates and reduced final size of mature prepupa reared on
FS indicated the need to search for suitable co-substrates
and establishment of an appropriate feeding strategy for
improvement of growth performance, survivorship, food
conversion ratios and reduction larval size variations. This
will contribute to increased biomass production efficiency
and waste reduction capacity, making BSF technology
attractive to faecal waste bioremediation.
In order to optimise waste reduction of mixed organic
waste and growth of BSFL, the current study sought to
establish a feeding strategy for BSF larvae reared on FS
material and other common organic wastes collected from
Kenya’s urban slum areas. Specifically, the study evaluated
the effect of different feeding rates, feeding regimes and
supplementation with locally available organic waste
streams on the BSFL productivity (larval growth rates and
yield) faecal waste reduction efficiency (substrate reduction,
feed conversion ratio and bioconversion rate) and nutrient
profile of the larval biomass product.
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Optimal feeding strategy of BSFL fed on faecal sludge and organic waste
Journal of Insects as Food and Feed ##(##) 3
2. Materials and methods
Study area and source of substrates
The study was done at Sanergy Ltd, a company that has
developed sanitation infrastructure solutions for human
excreta management involving building a network of low-
cost toilets/sanitation centres in informal settlements
within Nairobi City, Kenya. The sanitation centres are
urine-diverting dry toilet systems that separately deposits
urine and faeces in airtight containers; these are collected
daily and transported to a central facility for processing into
either biogas, insect-based animal feed, organic fertiliser
or electricity (http://www.sanergy.com/approach). FS used
in the study, were sourced from daily collections from the
toilets/sanitation centres in the sprawling Mukuru Kwa
Njenga informal settlements in Nairobi City.
The brewer’s waste was collected from East African
Breweries Limited, Nairobi, while the post-consumer
restaurant food waste was obtained from the eateries
located at Kinanie trading centre, whereas BP were sourced
from the local Kinanie market as previously described
(Nyakeri et al., 2017).
Black soldier fly larvae
The larvae for the current study were obtained from a
BSF colony established at Sanergy’s production site under
constant climatic conditions (28±2.0x, 65±5.0% relative
humidity). Corrugated plastic pipes were put on putrescent
food remains inside 5 litre plastic basins for adult females
to lay eggs on. The putrescent waste served as an attractant
medium to the female adults. Pipes containing eggs laid
within two days were collected and transferred to a plastic
container containing 15% protein chick mash thoroughly
mixed with water to moisture content of 60% for hatching.
Hatching was observed after 4-5 days. To ensure optimal
larval development, the newly hatched neonates were
allowed to feed on the commercial chick mash until they
were 5 days old.
On the 6
th
day, the larvae were sieved through a 1.2 mm
diameter mesh screen and those that passed through
were considered of the same size and weight. Sampling
was done by initially counting the larvae into two groups
each containing 2,000 larvae, using a pair of forceps to
handle the delicate larvae. Each group was then weighed
on an electronic weighing scale to determine the average
collective weight of 2,000 larvae, and consequently the
mean initial weight per larvae before. The average weight
of a cohort was then used to divide the rest of the larvae
into 36 cohorts, each to be distributed onto the feeding
containers designated for the respective treatment (feeding
rate, substrate co-mixing and feeding regime). The larva
transferred onto the feeding trays had an average weight
of 0.0029 g/larva.
Experimental design
Influence of feeding rate
To test the effect of feeding rate on larval growth rate and
substrate reduction efficiency, BSF larvae was reared on
FS as the principal substrate under four different feeding
rates: 100, 150, 200 and 250 mg/larva/day.
Influence of feeding regime
Comparison of larval growth rate and substrate reduction
efficiency was also done on FS under different feeding
regimes, namely daily feeding (DF), after four days feeding
(AFD), weekly feeding (WF) and lump sum feeding (LF).
Substrate distribution was done according to the individual
feeding regimes: DF, AFD, WF and LF for FS only. The total
amount of food distributed into each basin was calculated
on the basis of number of larvae, feeding rate of 200 mg/l/d
and number of days to the next feeding period. After food
distribution, each larval cohort was evenly spread on the
allocated feedstock ration.
Influence of substrate supplementation
In order to determine an ideal co-substrate for FS (the
primary substrate at Sanergy Ltd), three readily available
organic wastes (food remains; FR, brewers waste; BW and
banana peels; BP) were combined with FS in three different
ratios (30:70, 50:50, and 70:30) and compared to the control
diet (100% FS). The amount of food substrate fed to 2,000
larvae was provided in four batches of four days each and
was calculated proportionately according to the feeding rate
of 200 mg/l/d and ratio of mixing the principal substrate
(FS) and the co-substrate and each weighed accordingly.
The two were then thoroughly mixed in large plastic bowls
to obtain homogeneity before distribution into the feeding
basins.
All larval feeding experiments were done under the existing
conditions of temperature (28±2.0°C), relative humidity
(65±5.0%) of the environment and the moisture content of
the feedstock. Each larval cohort was spread evenly on its
allocated substrate for feeding in triplicates. The feeding
containers were then randomly placed on a floor surface
and covered with a mosquito netting to keep off other fly
species from laying on the substrates.
Generally, BSF larvae are dull whitish in colour, until they
approach the prepupal stage (5th larval stage), where they
undergo a marked colour change to dark brown, cease
feeding and migrate out of the substrate prior to pupation
(Caruso et al., 2014; Diener et al., 2011b; Schremmer,
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E.M. Nyakeri et al.
4 Journal of Insects as Food and Feed ##(##)
1984). In all the treatments, feeding was done for 16 days
but harvesting was done when prepupae (recognised by a
change of colour of the integument from white/cream to
dark/brown) was observed.
Sampling and harvesting
For all treatments, sampling was done on every 4th day by
randomly counting 300 larvae from each container. The
sampled larvae were collectively weighed on an electronic
scale and thereafter, returned to their respective feeding
containers. The total weight obtained was divided by the
number of larvae to obtain an average weight of each
larva. The weight gain after every 4 days was calculated
by comparing the obtained average larval weight with the
previous mean larval weight. The final prepupa weight
was taken to be the average weight recorded on the day of
harvest. On the last day of sampling, all the prepupa and any
remaining larvae in a treatment were separately harvested
by sieving through a 5 mm dimeter mesh screen. This was
supplemented with manual picking of small sized larvae
that may have passed through the sieve together with the
residue to minimise losses. The biomass and residue weight
obtained were weighed and recorded. Thereafter, the weight
of total feed provided and that of total residues obtained
were used to calculate the reduction effect of a treatment.
The performance of the different treatments was evaluated
using the recorded parameters of periodical larval weights,
total prepupal/larval harvests in grams, and calculation of
feed conversion and reduction efficiency.
Substrate consumption and reduction efficiency
The efficiency of the BSFL to consume and therefore
reduce organic matter content in the fed substrates at a
uniform feeding rate of 200 mg/larva/d was determined
by calculating waste reduction efficiency, feed conversion
into body mass efficiency (feed conversion rate; FCR) and
bioconversion rate, as described previously (Banks et al.,
2014; Diener et al., 2009).
Nutritional analysis
A sample of harvested prepupa from a treatment were
blanched in hot water for 5 minutes and then sun dried in
a greenhouse for 4 days at an average temperature of 35°C.
The dry biomass was then ground into powder using a
kitchen blender. For protein content (CP) analysis, micro-
Kjeldahl method was used as described previously (Nyakeri
et al., 2016). For the analysis of ether extracts (EE), 2 g of
Table 1. Mean (±SE) prepupal yield, days to maturity, substrate reduction, bioconversion rate and feed conversion ratio of black
soldier fly larvae grown on faecal sludge.1
Parameter Feeding rate
(mg/larva/day)
Prepupal yield
(mg/prepupa)
Development
time (days)2
Substrate
reduction (%)
Bioconversion
rate (%)
Feed
conversion rate
Faecal sludge
100 124±3.0b20a81±8.9a21±2.5b3.9±0.1a
150 140±1.3b18b84±0.3a29±0.3a2.9±0.0b
200 176±3.3a16.7bc 57±1.1b21±0.8b2.8±0.1b
250 190±1.2a15c54±1.2b23±0.6ab 2.4±0.0c
Swine manure Newton et al. (2005) N/A N/A N/A ~39 3.97 9.6
Chicken manure Sheppard et al. (1994) N/A 220 N/A ~50 3.74 13.4
Municipal organic
waste
Diener et al. (2011a) N/A 220±0.0 N/A 68 11.78 145
Fresh human faeces Banks et al. (2014) N/A 108 N/A 46 22.3 2.0
Food waste3100 210±10 12.5±0.7 65.4±4.1 17.98±0.57 3.9±0.5
Faecal sludge3100 ND4
Food waste – human
faeces mix (95:5)5
40 221±2.5 – 84.5 19.0±2.3 NA
60 224±2.9 – 85.5 18.9±3.4 NA
1 Means within a column having different letters were statistically different at P<0.05 (ANOVA, Tukey post hoc tests).
2 The numbers of days taken for prepupae to emerge from the larvae.
3
Experiments done at larval density of 2 larvae/cm
2
and incremental feeding regime of every three days, until 50% of the larvae had turned into prepupae (Joly, 2018).
4 ND = no growth observed when food was supplemented with faecal sludge.
5 A continuous BSF composting system (larveros), where 2,750 and 4,150 larvae were added in 60 (FR-60) and 40 (FR-40) mg dry food/larva/day feeding regimes,
respectively (Dortmans, 2015).
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Optimal feeding strategy of BSFL fed on faecal sludge and organic waste
Journal of Insects as Food and Feed ##(##) 5
ground sample was transferred into labelled crucibles.
70% pure diethyl ether was added to each sample and the
mixture transferred to an ether extractor machine. After
extraction, the EE was dried in an oven at 110°C for 30
min before weighing to determine the net weight of the
extract. All analyses were done in triplicates.
Statistical analysis
The recorded parameters for the substrate trials included
total larvae/prepupal yield (g, dry mass weight), individual
wet larvae weight (g), substrate reduction, bioconversion
and FCR for the different feeding treatments. All the
experiments were done in triplicates. The data was
subjected to two-way ANOVA to determine significant
differences between means. Tukey HSD method was used
for mean separation between treatments at 95% confidence
level. All statistical analysis were performed using the R
computing environment in R studio (https://www.rstudio.
com/products/RStudio).
3. Results and discussion
Influence of feeding rate on larval performance
In this study, feeding rate of FS had a significant effect on
larvae growth rate and development time (Table 1). This
effect was more pronounced from day 4 onwards, with
higher feeding rates resulting in faster growth (Figure 1A).
Consistent with results from other reported studies (Diener
et al., 2009b; Mutafela, 2015), this observation implies that
food requirements varies with time over larval growth cycle,
with older larvae consuming more food than younger larvae.
In terms of larval development time, BSFL reared on 200
and 250 mg/larva/day FS developed significantly faster
(P<0.05), the first prepupae were observed after 14 days
and significant proportion (>50%) moulting by 16 days.
In contrast, larvae fed on 100 and 150 mg/larva/day FS
diet developed the slowest with prepupae emerging not
before 16 and 15 days, respectively. In addition, on the latter
feeding rates it took approximately 30 days for all larvae to
moult into prepupae, about 8 days longer than at feeding
rate of 200 and 250 mg/larva/day.
Overall, the prepupal yield improved with increasing
feeding rate of FS. Larvae fed on 100 and 150 mg/larva/
day FS gave a yield of 124±3.0 and 140±1.3 g, respectively
(wet weight basis). In contrast, substantially higher prepupal
yield (P<0.05) of 176±3.3 and 190±1.2 g was obtained at
feeding rates of 200 and 250 mg/larva/day, respectively. The
observation that biomass gain and substrate conversion
was not significantly different between larva reared at
feeding rates of 200 and 250 mg/larva/day, indicates that
a feeding rate of 200 mg/larva/day for FS was ideal under
our experimental conditions. These results are comparable
to the different optimum feeding rates reported for different
substrates in literature (Table 1).
The appropriate amount of a feed resource to provide
the larvae generally may vary depending on the type
and nutrient quality of the resource. An individual BSF
larvae can consume between 25-500 mg/day of substrate
depending on the nature of the feedstock particle size,
nutritional quality moisture and fibre content (Spranghers et
al., 2017; Veldkamp et al., 2012). Although not analysed in
this study, documented biochemical analysis of the FS shows
that it constitutes of 2-25% nitrogen content depending
0 4 8 12 16
0
50
100
150
200
250
300
0
50
100
150
200
250 ***
***
*
B
Mean larval weight (mg/pp)
Maen larval weight (mg)
Day
0 4 8 12 16
Day
200 mg/l
250 mg/l
150 mg/l
100 mg/l
DF
LF
WF
AFD
**
*
A
Figure 1. Black soldier fly larvae wet weight in mg per prepupa or larvae (arithmetic mean ± SD), over 16 days as affected by
feeding rates and feeding regimes of faecal sludge. In (A) the results represent a mean weight of 200 larvae (in three replicate
treatments) fed at a rate of 100, 150, 200 and 250 mg/larva/day. (B) contains data from replicates (n=3) of 200 larvae fed at different
feeding regimes: daily feeding (DF); after four days feeding (AFD); weekly feeding (WF); and lump sum feeding (LF). The equivalent
feeding rate was maintained constant at 200 mg/larva/day. Days denoted by *, ** and *** indicate significant difference (ANOVA
followed by Tukey post hoc tests) at P≤0.05, P≤0.01 and P≤0.001, respectively. PP = prepupa.
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E.M. Nyakeri et al.
6 Journal of Insects as Food and Feed ##(##)
on factors such as diet, a high microbial load of 25-54%
mostly bacteria, 25% carbohydrate and 2-15% fat (Banks
et al., 2014). FS used in the experiments were collected
from an informal settlement, whose inhabitants live on
an income below US$ 1/day and diet consisting of cereals
and green vegetables indicating low protein quality of the
resultant wastes. In addition, the faecal matter is mixed
with sawdust to moderate moisture content, eliminate smell
and facilitate easier handling; these are collected every day,
transported to central processing unit and accumulated in
heaps before use in larval feeding. Performance of BSFL
has been reported to be higher in fresh faeces compared
to pit latrine faeces (Banks et al., 2014). Banks et al. (2014)
attributed the associated stock piling of faecal substrates in
pit latrine with the development of anoxic conditions which
do not favour the feeding or survival of BSF larvae, but also
leads to reduced protein content. The practice of mixing FS
with sawdust at the point of collection and accumulation
in heaps before use in larval feeding further deteriorates
the quality of faecal waste streams. Consequently, the
nutritional imbalance due to aforementioned practices,
may account for the observed higher feeding rates of larvae
reared on FS to compensate for deficient nutrients and
longer development time (Table 2).
Effect of feeding regime on larval growth, development
time and prepupal yield
With exception of differences observed at day 8 and 12,
different feeding regimes had no significant effect on larval
development rate (Figure 1B) at constant feeding rate of
200 mg/larva/day. Substrate reduction, bioconversion and
feed conversion rates between 77.1-84.6, 2.56-3.15 and
26.1-30.4%, respectively, were comparable for all feeding
regimen treatments (Table 2). Interestingly, there was no
significant difference in prepupal yield (P=0.56) of larvae
reared on FS at different feeding regimes when feeding
rate was kept constant at 200 mg/larva/day. However, we
observed that larvae fed periodically (DF, ADF and WF
feeding regimen) took significantly shorter time (3-4 days,
P<0.001) for prepupa to emerge than when subjected to
batch feeding (LF regimen) (Table 2). The results of the
study showed that periodical feeding regimen resulted
in shorter development time, indicating that exposure
to fresher feed stimulated faster larval growth and
development into prepupa. Comparable with our results,
Banks et al. (2014) reported that BSFL fed on fresh faeces
every 2 days developed faster than the larvae fed once
at the beginning of the experiment (similar to lumpsum
feeding in our study). In the study, the authors attributed
the observation to nutritional imbalance (lower protein)
associated with stockpiling of feed in lump sum diet leading
to an increase in development time and larval size. This
supports the hypothesis that reduced protein content in
the lump sum diet causes a nutritional imbalance that
leads to compensatory feeding in BSFL (Banks et al., 2014).
Consequently, different studies have utilised incremental
feeding regimen when using faecal sludge as substrate
(Dortmans, 2015; Joly, 2018)
Performance of larva when fed on FS or FR at different
feeding rates either on daily (periodical) feeding or
lumpsum (batch) feeding regime was also compared
(Figure 2). Overall, prepupal yield of lumpsum fed larva
was significantly higher (P<0.05) than those fed daily
feeding across all feeding rate of FR (Figure 2A), whereas
no substantial difference (P=0.965) was observed between
two feeding regime treatments for FS (Figure 2B). However,
prepupal yield on FS was more dependent on feeding rate
than feeding regime. In line with findings on FR, Mutafela
(2015) and Barragan-Fonseca et al. (2018) reported that
batch feeding (equivalent to LF) gave higher larval growth
compared to the continuous feeding regime (equivalent to
DF). Higher prepupal yield of BSF larva at higher feeding
indicated that larval response was directly proportional to
the amount of supplied food, with larvae being stimulated
Table 2. The effect of different feeding regimes on mean (±SE) prepupal yield and days to maturity of black soldier fly grown on
faecal sludge, and the corresponding substrate reduction, bioconversion rate and feed conversion rate.1
Parameter Feeding regime2P-value
ADF DF WF LF
Prepupal yield (mg/prepupa) 201±7.4 194±3.1 202±6.1 204±2.1 0.56
Larval development time316b16b17b20a<0.001
Substrate reduction (%) 83.5±0.3b84.6±0.2a79.2±0.1c77.1±0.1d<0.001
Feed conversion ratio 3.2±0.1a3.1±0.1a3.0±0.1a2.6±0.1b0.003
Bioconversion rate (%) 26.6±1.1b27.9±0.4ab 26.1±0.5b30.2±0.9c0.019
1 Means within a row having different letters were statistically different at the indicated P<0.05 (ANOVA, Tukey post hoc tests).
2 AFD = after four days feeding; DF = daily feeding; LF = lump sum feeding; WF = weekly feeding.
3 The numbers of days taken for prepupae to emerge from the larvae.
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Optimal feeding strategy of BSFL fed on faecal sludge and organic waste
Journal of Insects as Food and Feed ##(##) 7
to eat more on a regimen that provided large amounts of
food at once (Figure 2B). Mutafela (2015) also reported
that larvae fed periodically took an average of 2-3 days
longer to mature compared to those on batch mode. The
study attributed findings to possible adjustment by BSF
larva to less food by lowering their metabolism during the
periodical feeding regimes.
Influence of feed supplementation on growth, prepupa
yield and development time
Previously, we reported poor overall performance of FS
as a substrate for rearing wild BSFL when compared to
other organic wastes (Nyakeri et al., 2017). In this study, we
assessed how the performance of FS, principal feed substrate
at Sanergy Ltd for BSFL production, can be improved by
supplementation at different levels with locally available
organic waste feedstocks. Table 3 illustrates the results on
the effect of FS supplementation with other organic waste
feedstocks on biomass production, substrate reduction,
and time taken to larval maturity. All tested parameters
improved when the FS was supplemented with a co-
substrate. A significantly higher prepupal yield and shorter
development time (P<0.05) was observed on blending FS
with other organic waste as a co-substrate, irrespective
of supplementation level (Table 3). Optimal performance
was achieved at both 30 and 50% supplementation level
of all co-substrates. Supplementing FS with FR 30, 50 and
70% gave relatively higher prepupal yield (295, 270 and
253 g, respectively), compared to brewer’s waste (270, 261
100 150 200 250
0
20
40
60
80
100
b
b
ba
a
a
b
a
B
Feeding rate (mg/larva/day)
A
100 150 200 250
0
20
40
60
80
100
aa
a
a
a
a
a
a
Daily feeding
Lumpsum feeding
DF LF
0
20
40
60
80
b
b
a
a
a
a
a
a
C
Feeding regime
Feeding rate (mg/larva/day)
Feeding regime
DF LF
0
20
40
60
80
b
b
ab
b
b
ab a
a
D
100 mg/larva/day
150 mg/larva/day
200 mg/larva/day
250 mg/larva/day
Larval yield (g)
Larval yield (g)
Larval yield (g)
Larval yield (g)
Figure 2. Mean (± SD) black soldier fly larval yield (g dry matter) at various feeding rates and feeding regime. The effect of batch
(lumpsum) and periodical (daily) feeding on larval yield at different feeding rates when reared on food remains (A) and faecal
sludge (B) were compared. Results using feeding regime as grouping variable to illustrate the subtle differences observed for
food remains (C) in comparison to faecal sludge (D) when varying feeding rates is also presented. Means within a group having
different letters were statistically different at the indicated P<0.05 (ANOVA, Tukey post hoc tests).
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E.M. Nyakeri et al.
8 Journal of Insects as Food and Feed ##(##)
and 196 g) and BP (253, 238 and 197 g). Similar to our
results, Joly (2018) reported that BSF larvae developed
faster and gave better yield on a mixture of food waste
and FS compared to FS alone. The observed improved
performance in this study may be attributable to improved
nutrient quality due to supplementation.
The heterogenicity of waste feedstock due to mixing of
different organic wastes have previously been reported
to improve substrate quality related to diet composition,
increased nutrient content and feedstock structure (Bullock
et al., 2013; Joly, 2018; Spranghers et al., 2017). In this study,
FR – sourced from restaurants and eateries around study
site – consisting of a mixture of ugali (corn paste), rice,
vegetables and meat/fish bones, is comparatively highly
heterogeneous and nutritionally superior to the other co-
substrates used. These improvements could account for the
observed higher larval consumption rates, biomass increase
and shortening of development time on supplementing
FS with organic waste co-substrates compared FS alone.
Studies on BSF and other insect species have also shown
that the protein content of the feed resource is important.
For example, larvae of noctuid caterpillars (Lepidoptera:
Noctuidae) and acridid grasshopper nymphs (Melanoplus
bivittatus; Orthoptera: Acrididae) fed on carbohydrate-
based diets have been reported to take longer to mature
than those feeding on other diets (Le Gall and Behmer,
2014). Nash and Chapman (2014) also reported significantly
slow development of larvae of the Mediterranean fruit fly
(Ceratitis capitata, Wiedemann; Diptera: Tephritidae) when
reared on a low-protein diet despite the high carbohydrate
content. Oonincx et al. (2015a) recorded significantly faster
development and greater survival rate when BSF larvae were
reared on a food waste diet high in protein (22%) and high
in fat (9.5%). In terms of nutrition, BSF larvae have been
reported to perform better on feedstock with protein levels
lower than ca. 30%, and are better bioconverters of plant
proteins than animal proteins (Nguyen et al., 2015). Due
to their omnivorous nature, the feed fat and carbohydrate
content should be similar to or lower than protein levels
Table 3. Influence of faecal sludge supplementation with other organic waste feedstocks on black soldier fly larvae (BSFL)
biomass production, substrate reduction, time taken to larval maturity and harvested BSFL nutrient composition. All results are
presented as means ± SEM.1
Substrate supplementation ratios2Prepupal yield (g) Days to maturity (days) Substrate reduction (%) Feed conversion rate
Faecal sludge 170±7.4 22.3±0.3 61.5±2.3 2.89±0.32
Food remains
30% 295±6.5a14.0±0.0a92.5±0.2a4.62±0.10a
50% 299±4.4a14.0±0.0a88.0±0.0b4.67±0.07a
70% 263±5.1b16.0±0.0b88.2±0.6b4.12±0.08b
Brewer’s waste
30% 270±4.5a15.3±0.3 63.6±0.0b4.22±0.07a
50% 261±3.4a15.0±0.0 69.7±0.0a4.08±0.05a
70% 196±7.3b15.0±0.0 63.1±0.0b3.07±0.11b
Banana peelings
30% 253±2.7a24.3±0.3a56.1±0.6c3.95±0.04a
50% 238±5.0a20.0±0.0b63.1±0.1b3.72±0.08a
70% 197±2.9b17.7±0.3c67.1±0.6a3.07±0.05b
Food waste – human faeces mix (95:5)3
FR-40 221±2.5 10 84.5 19.0
FR-60 224±2.9 10 85.5 18.9
Food waste-dewatered faecal sludge mix4
FW100 210±10 12.5±0.71 65.4±4.1 3.89±0.51
FW50 ND5ND 35.8±0.6
FW0 ND ND 29.4±0.2
1 Means of groups within a column having different superscript letter are statistically different at P<0.05 (ANOVA, Tukey post hoc tests).
2 BP = banana peelings; BW = brewer’s waste; FR = food remains; FS = faecal sludge. The level of percentage supplementation (wet weight basis) of the FS is shown.
3 Results from a continuous BSF composting system (larveros), larvae were fed food waste-human faeces mixture at a rate of 60 (FR-60) and 40 (FR-40) mg dry
food/larva/day (Dortmans, 2015).
4 BSF reared on food waste supplemented with increasing ratio of slightly dewatered faecal sludge: 100:0 (FW100), 50:50 (FW50), and 0:100 (FW0), at density
of 2 larvae/cm2 and an incremental feeding regime of every three days (Joly, 2018).
5 ND = no growth observed when food was supplemented with faecal sludge.
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Optimal feeding strategy of BSFL fed on faecal sludge and organic waste
Journal of Insects as Food and Feed ##(##) 9
(Nguyen et al., 2015; St Hilaire et al., 2007; Tschirner and
Simon, 2015). Therefore, the results that supplementation
of FS with other nutrient-superior organic wastes gave
comparatively significant higher performance (P<0.05)
in terms of prepupal yield (FR>BW>BP>FS), illustrate
the advantages and potential utility of supplementation
to improve BSFL performance on inferior organic waste
substrates.
However, a common challenge observed across all
mixed feed treatments was variability in the larval sizes,
comparable to pure FS. This phenomenon could be
attributed to the heterogeneous nature of the diet and
different particle sizes that made mixing to get homogenous
substrate mix inefficient. Inefficient mixing of substrates
can lead to zoning of substrate components. This can
result in different parts of the substrates having varied
nutrient concentration and moisture content. This may
lead to variability in larval sizes (Brits, 2017), and therefore,
thorough mixing of the substrates mixture is critical to
ensure uniform and homogeneous mix.
Effect of supplementation on bioconversion and waste
reduction efficiency
Bioconversion and FCR are effective and simple methods
for calculating feeding efficiencies of the BSF larvae (Banks
et al., 2014; Cammack and Tomberlin, 2017; Zhou et al.,
2013). In addition, substrate dry matter reduction is also
meant to give an indication of how sufficiently the substrate
is degraded and converted to larval biomass. In this study,
relatively high substrate reduction levels ranging between
54 to 92.5% was obtained (Table 1). These results were
comparable and even in some cases better than those
reported for other substrates (Barry, 2004; Diener et al.,
2011a; Liu et al., 2008). This indicated that BSFL were
able to consume and significantly reduce the organic waste
across all treatments without significant negative effects
on feeding efficiencies. However, variations were observed
within and between the different treatments due to the
nature and quality of the substrates used.
With exception of FR-FS mix, increase in supplementation
of other co-substrates to 70% resulted in reduced yield
of prepupa biomass, bioconversion and waste reduction
compared to 100% FS (Table 3). In literature, a few authors
have highlighted the importance of feedstock structure in
the bioconversion process by BSF. Several studies have also
pointed out that the feedstock should have enough structure
to allow the larvae to move through the material, consume
it, and get an adequate supply of oxygen (Barry, 2004; Brits,
2017; Joly, 2018). In contrast to FR that is characterised by
coarse structure, the fine structure of brewer’s waste may
have hindered larval movement and aeration within the feed
mix when supplemented at higher ration. Consequently,
supplementing FS with FR at higher ration led to improved
aeration, moisture moderation and facilitated larval
movement within the feed, coupled with better nutrient
quality, resulted in higher BSFL biomass yield and waste
reduction efficiency observed. Interestingly, waste reduction
efficiency in FS-BP mix increased with increase in the co-
substrate ration level, despite no corresponding increase
in biomass yield. Proximate analysis showed high moisture
content of BP (Nyakeri et al., 2016), and hence, high waste
biomass loss over time could also be attributed to drying
up process. However, the high of bioconversion rates and
substrate reduction efficiency obtained in the current study
indicated that the substrates used are highly digestible and
were assimilated into larval biomass.
Proximate composition of BSF prepupae
In this study, the influence of supplementing FS with 30%
of other local available organic waste on BSF prepupae
proximate composition was investigated (Table 4). The CP
of prepupal biomass was comparable among the treatments,
ranging between 432 and 478 g/kg DM. These crude protein
content values were in the range reported for similar waste
substrates in literature (Table 4). Whereas prepupae fed on
FS-BP (BP30) mix gave substantially lower (P<0.05) CP
(432 g/kg DM), differences in CP values for those fed on
other substrate mixes was small, indicating that low protein
content substrates also resulted in high crude larval protein.
These results are in line by findings of Barragan-Fonseca et
al. (2018) and Spranghers et al. (2017) who reported that the
protein content and amino acid profile of BSF prepupae is
not dependent on protein content and quality of the waste
stream they are reared on. However, feeding of BSF larvae
on nutritionally superior high-protein substrates such as
liver or meat have also been reported to result to higher
protein content (~60%) than on vegetable table wastes (38%
DM) (Nguyen et al., 2015).
It has been reported that, as the prepupa ages, the protein
content decreases due to sclerotisation, a process which
causes enzymatic degradation of proteins to build up the
chitin layer of the exoskeleton (Aniebo and Owen, 2010).
When moulting into pupae, cuticle become rigidified due
to accumulation of calcium salts forming a dark envelope;
these changes also may lead to low nutritional quality
and digestibility of harvested BSFL (Caruso et al., 2014).
Chitin-corrected protein content is therefore considered
a good measure of available protein, due to its negative
influence on protein digestibility (Janssen et al., 2017).
Different studies have reported chitin levels between 38-
87 g/kg in BSF prepupae (Diener et al., 2009; Finke, 2013;
Spranghers et al., 2017). Previously, we had shown that
the crude protein content decreases with increase in age
of the larvae, irrespective of the rearing substrate used
(Nyakeri et al., 2017); and consequently, BSF prepupa
should preferably be harvested before the exoskeleton is
fully hardened. In this study, harvesting prepupa at day 14,
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10 Journal of Insects as Food and Feed ##(##)
where BSF prepupae started to emerge from the larvae,
was a better trade-off between average yield with minimal
chitin level for maximal protein content and digestibility.
Chitin-corrected CP content for BSF prepupae reared on
different substrate mixes under study, taking into account
the reported chitin values in the literature (Diener et al.,
2009; Spranghers et al., 2017) and suggested conversion
factor of 4.67 (Janssen et al., 2017), ranged between 345-
440 g/kg DM. These values are still within the range of
CP content reported for BSF prepupae reared on other
substrates in literature (Table 4).
In contrast to CP values reported above, the variability of
BSF larval crude fat (EE) content was dependent on the
substrate type, with values ranging between 182-227% DM
(Table 4). Rearing of BSF prepupae on BP30 recorded a
significant higher (P<0.05) EE content (227±1.5 g/kg DM)
when compared to other substrate mixes (<20% DM EE
content). Despite the crude fat being within the range of
values in literature (7-39% DM), the EE content reported
were substantially lower than those reported for BSF
prepupae fed on nutritionally superior substrates such as
chicken feed (33.6%), vegetable waste (37%) and restaurant
waste (38.6%) (Spranghers et al., 2017), and oil rich food
waste (42-49%) (Barry, 2004). The current values recorded
are in line with our previous findings for wild BSF reared
on FS (~18% DM) (Nyakeri et al., 2017). However, the
crude fat values recorded for substrate mixes in this study
were still significantly lower compared to those for wild
BSF prepupae fed on FR (35.9% DM), BP (38% DM) and
BW (27.2% DM) without supplementation. Several authors
have observed that BSF prepupae fed on high-fat and
carbohydrate diet had a higher crude fat content than those
fed on high-fibre or low-fat diets (Barragan-Fonseca et al.,
2018; Nguyen et al., 2015; Zhou et al., 2013). Our findings
indicate that the low crude fat content of BSF prepupae
could be attributed to poor quality of FS, probably due to
sawdust addition to FS that increases the fibre content of
the substrates. Furthermore, 30% supplementation of FS
with other organic substrate did not markedly improve the
crude fat content of the BSF larvae; therefore, follow up
studies targeting altering BSF crude fat content by varying
FS fat, carbohydrate and protein content by supplementing
with other organic wastes is required. Despite variability
in CP and EE values, all values consistently point to BSF
prepupae reared on FS supplemented with various organic
waste substrates as a good source of proteins and lipids.
These results further points to the resilience of BSF larva to
grow and produce valuable product on nutritionally-inferior
sanitation residues under variable conditions.
From application perspective, BSF larva meal with higher
CP:EE ratio such as those fed on FS, FR and BW (>2.4
CP:EE ratio) are desirable, as high fat content could
limit its application as animal feed ingredient. However,
high fat content BSF prepupae can also be utilised for
dual application in the production of biodiesel (where
fat component is extracted for oil) (Li et al., 2011)) and
the resultant meal (high in protein) can be used as feed
ingredient. Currently, most conventional animal feeds
Table 4. Proximate composition (means ± SE, dry matter) of black soldier fly reared on faecal sludge supplemented with 30%
co-substrate organic wastes.1,2
Substrate Crude protein (g/kg) Ether extract (g/kg) CP:EE ratio Data adapted from3
Faecal sludge (FS100) 462±0.7a184±0.5a2.51
Food remains (FR30) 461±0.4a182±0.4a2.53
Brewer’s waste (BW30) 478±0.5a196±0.5a2.44
Banana peelings (BP30) 432±1.1b227±1.5b1.90
Food waste 361±0.1 359±0.1 1.00 Nyakeri et al., 2017
Brewer’s waste 430±1.0 272±1.0 1.58 Nyakeri et al., 2017
Banana peels 349±0.6 380±0.3 0.91 Nyakeri et al., 2017
Poultry manure 476 253 1.88 Aniebo and Owen, 2010
Municipal organic waste 398 301 1.32 Mutafela, 2015
Cow manure – 424.2 – St Hilaire et al., 2007
Chicken feed 412 336 Spranghers et al., 2017
Biogas digestate 422 218 Spranghers et al., 2017
Vegetable waste 399 371 Spranghers et al., 2017
Restaurant waste 431 386 Spranghers et al., 2017
1 Means of groups within a column having different superscript letter are statistically different at P<0.05 (ANOVA, Tukey post hoc tests).
2 CP = protein content; EE = ether extract.
3 Have been included for comparison.
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Journal of Insects as Food and Feed ##(##) 11
in Kenya and East Africa are made from Omena, small
silver cyprinid fish (Rastrineobola argentea) harvested from
Lake Victoria as the main source of animal protein. The
imbalance of supply and demand mainly due to overfishing
and competition for Omena for food has, however, led
to price increases of the fishmeal in the last 5 years. In
addition, inconsistent quality of Omena delivered to feed
millers usually mixed in with a lot of other materials,
including sand, shells, and other fish, is a major concern
to farmers as low quality Omena fishmeal results in poor
animal growth (Kariuki, 2011). Several trials in Kenya and
elsewhere have demonstrated that BSF larvae protein can
successfully be used to partially or completely substitute
the more expensive protein sources such fish meal or soy
bean meal for poultry, rabbits and aquaculture feeds (Dalle
Zotte et al., 2018; Mwaniki et al., 2018; Onsongo et al.,
2018; Secci et al., 2018). For BSF larva meal to be a viable
and sustainable substitute for fish meal and soybean meal
in animal feeds, considerably high quantities of insect are
required. Therefore, promotion of BSF mass production
by small- and large-scale enterprises for animal feed
protein from different organic waste substrates, and the
potential for income generation and job creation is currently
underway worldwide.
For mass production of BSF larva, a constant supply
of cheap organic waste stream is important to lower
production cost and make it attractive as an investment.
It is estimated that about 60% of Nairobi’s four million
inhabitants live in its informal settlements and generates
2,400 tonnes of solid wastes daily; three-quarters of the
waste are mainly household organic waste (Kasozi and Von
Blottnitz, 2010; Von Blottnitz and Ngau, 2010). In addition,
approximately 72,000 kg (~300 g/person/day per adult) of
FS is produced daily from the informal settlements that can
potentially be harnessed for mass BSF larva production.
A high waste-to-biomass conversion rate of up to 20-29%
on wet weight basis reported in this study demonstrated
that satisfactory yield of BSF larva can be achieved on FS
supplemented with other organic wastes with concomitant
appreciable organic waste reduction. These results support
the utility of FS and common organic wastes substrates in
mass BSF larva production can provide the much-needed
incentive for organised collection and processing of these
wastes from informal settlements where human faecal
and organic waste management system is non-existent. It
is imperative, if well implemented, BSF technology can be
an example of sustainable solution in providing valuable
ecosystem services aimed at ameliorating the common
sanitation and environmental problems associated with
untreated faecal and organic waste in these environments.
This study has provided a guideline on optimisation of BSF
larva production on nutritionally inferior substrates through
co-substrate supplementation. However, large experiments,
taking into account the intricate logistics involved in FS
and household organic waste collections and processing,
are required to determine the extent to which these results
can be replicated in mass production systems.
4. Conclusions
In conclusion, our findings demonstrated that
supplementation of FS with other organic waste can be used
to improve its suitability as a substrate for BSF production
and bioremediation from the environment. Higher biomass
production was obtained at supplementation rate of 30%
followed by 50%. Furthermore, BSF maturation period,
obtained bioconversion rate, substrate reduction and
nutrient content were either comparable or higher than
those for pure FS as a feed feedstock, and therefore,
supporting supplementation of the inferior feedstocks
to achieve better performance. Though growth rate of
larvae is directly proportional to the feed rate, but inversely
proportional to substrate reduction efficiency, there is
a threshold amount of feed supply needed for optimal
performance. Considering the need to balance between
waste reduction of primary substrate (FS) and prepupa
biomass production, the study recommends the use of FS
and the co-substrates at the 70:30 ratio at feeding rate of
200 mg/l/g. The recommendation is supported by the high
BCR and FCR values obtained at this ratio and feeding rate
across all the treatments. On the basis of above findings
and the ease of local availability of feedstocks, FR, BW
and BP can potentially be utilised as co-substrates with
FS for sustainable production of BSFL and improving
bioremediation of FS both at small-scale and large-scale
level. The study recommends use of the identified substrates
for use in the farming of BSFL as a means of not only
supplying the much-needed protein alternative but also
for organic waste management.
Acknowledgements
We acknowledge Sanergy Ltd for allowing the use of their
facility for the experiments and the assistance of employees
during the study. This paper is a product of research
activities supported by ‘GREEiNSECT: insects for green
economy’ research consortium (http://www.greeinsect.
ku.dk), funded by the Danish International Development
Agency’s (DANIDA) Consultative Research Committee for
Development Research Fund and the World Bank funded
Africa Centre for Excellence for Insect Research for Food
and Feeds (ACE-INSEFOODS) (http://insefoods.jooust.
ac.ke) hosted at Jaramogi Oginga Odinga University of
Science and Technology. HJOO is very grateful to University
of South Africa (UNISA) Research Directorate for the award
of Visiting Researcher Fellowship.
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