Archivos Latinoamericanos de Producción Animal. 2024. 32 (3)
Consumption of expanded polystyrene by Tenebrio molitor
and Zophobas atratus, and use of their meal as feed for
Piaractus brachypomus
Recibido: 20240218. Revisado: 20240520. Aceptado: 20240708
1
Fundación Universitaria Agraria de Colombia.
2
Corresponding author: kbbarraganf@unal.edu.co
121
Miguel F. BonillaAmaya
Abstract. Expanded polystyrene (PS) provides a great challenge for environmental management due to its high levels
of production and insufficient waste management. However, recent studies have demonstrated the capacity of
Tenebrio molitor and Zophobas atratus to biodegrade PS, as well as the possibility of using the meal of these species to
feed fish. The objective of this study was to evaluate the effect of including insect meal as a substitute for fishmeal in
diets for Piaractus brachypomus fingerlings. In one experiment, the effect of 5 different levels of PS and wheat bran (WB)
was evaluated (100 % PS:0 % WB, 75% PS:25 % WB, 50 % PS:50 % WB, 25 % PS:75 % WB, and 0 % PS:100 % WB) on
growth and composition of T. molitor and Z. atratus larvae. In a second experiment, 10 different diets for Piaractus
brachypomus fingerlings were evaluated involving five levels (100, 75, 50, 25, and 0 %) of substitution of the fish meal of
a conventional dietary formulation with meal of T. molitor or Z. atratus previously fed with PS. In the first experiment,
the best treatment for both species was 25 % PS:75 % WB, resulting in the highest growth rate and consumption of PS.
In the second experiment, no significant differences were found among treatments for any of the variables evaluated
for productive performance for the fish. We conclude that up to 100 % of the fish meal in the diet of Piaractus
brachypomus fingerlings may be replaced with meal of T. molitor or Z. atratus fed with PS, although there is a need for
further studies regarding the longterm health effects on the fish and the humans that consume them.
Key words: cachama fish, circular economy, kingworm, mealworm, plastics
https://doi.org/10.53588/alpa.320301
Facultad de Medicina Veterinaria y de Zootecnia, Universidad Nacional de Colombia.
Bogotá, Colombia
Consumo de poliestireno expandido por Tenebrio molitor y Zophobas atratus, y
uso de su harina como alimento para Piaractus brachypomus
Resúmen. El poliestireno expandido (PS) representa un gran desafío para la gestión ambiental debido a sus altos
niveles de producción e insuficiente manejo de residuos. Sin embargo, estudios recientes han demostrado la
capacidad de Tenebrio molitor y Zophobas atratus para biodegradar el PS, así como la posibilidad de utilizar la harina
de estas especies para alimentar peces. El objetivo de este estudio fue evaluar el efecto de la inclusión de la harina
de estos insectos como sustituto de la harina de pescado dietas para alevines de Piaractus brachypomus. En un
experimento, se evaluó el efecto de 5 niveles diferentes de PS y salvado de trigo (WB) (100 % PS: 0 % WB, 75 % PS:
25 % WB, 50 % PS: 50 % WB, 25 % PS: 75 % WB y 0 % PS: 100 % WB) en el crecimiento y composición de las larvas
de T. molitor y Z. atratus. En un segundo experimento, se evaluaron 10 dietas diferentes para los alevines de
Piaractus brachypomus, se emplearon cinco niveles (100, 75, 50, 25 y 0 %) de sustitución de la harina de pescado de
una formulación dietética convencional con harina de T. molitor o Z. atratus previamente alimentadas con PS. En el
primer experimento, el mejor tratamiento para ambas especies fue 25 % PS: 75 % WB, lo que resultó en la tasa de
crecimiento más alta y consumo de PS. En el segundo experimento, no se encontraron diferencias significativas (p >
0.05) entre los tratamientos para ninguna de las variables evaluadas en el rendimiento productivo de los peces. Se
concluye que hasta un 100 % de la harina de pescado en la dieta de los alevines de Piaractus brachypomus puede ser
reemplazada con harina de T. molitor o Z. atratus alimentadas con PS, aunque se necesitan más estudios sobre los
efectos a largo plazo en la salud de los peces y de los humanos que los consumen.
Palabras clave: Cachama, economía circular, gusano rey, gusano de la harina, plásticos
Adriana P. MuñozRamírez
Fredy A. AguilarAguilar
1
Karol B. BarragánFonseca
2
122
Introduction
BonillaAmaya et al.
Consumption of plastic has quadrupled over the past
30 years, and global production of plastic has doubled
from 230 million tons in 2000 to 460 million tons in
2019 (European Bioplastics, 2018). Twenty years ago, it
was calculated that plastics accounted for 6080 % of
marine trash (Derraik, 2002), and currently they account
for 3.4 % of global greenhouse gas emissions (OECD,
2022). In 2013, the synthetic biopolymer polystyrene
(PS), commonly known as styrofoam, accounted for
approximately 7.1% (21 t/year) of all plastic consumed
(Plastics Europe, 2015). Currently, no environmentally
safe processes exist for efficiently degrading plastics.
The most widely used option is chemical management,
which may take several months, requiring nitric acid
and other corrosive substances with great
environmental impact (Gutiérrez, 2013).
On a global level, different technologies have been
developed to depolymerize PS more easily and more
naturally and rapidly achieve its final disposal through
biodegradation, by which biological action by fungi,
bacteria, and other microorganisms decompose the
material, progressively reducing its molecular weight
(Wenxiao et al., 2024; Tania & Anand, 2023; Kyrikou
and Briassoulis, 2007). Currently, insect species are
being used to degrade different types of waste (Khan et
al., 2021). This is the case of the coleopteras mealworm
(Tenebrio molitor, Linnaeus 1758) and kingworm
(Zophobas atratus, Fabricius, 1775), whose larvae are
capable of degrading different types of plastics,
including PS. For example, Jordan (2015) and Yang et
al. (2018) observed depolymerization of PS by larvae of
T. molitor, resulting in reduction of its molecular
weight, thereby facilitating its degradation.
Furthermore, the bacteria Exiguobacterium sp. has been
found to play an important role in biodegradation of
PS by these larvae by contributing to its
despolymerization (Yang et al., 2015a,b).
By 2050, the global human population is projected to
reach 9 billion, necessitating a 60 increase in food
production (van Dijk et al., 2021), ideally including
sustainable production of highquality animal protein
(Biasato et al., 2018). Feed costs, which account for 60
70 % of production expenses, are a major limitation to
increasing animal production (Khan et al., 2018;
Prodhan & Khan, 2018; Coffey et al., 2016; Van Huis,
2013). The urgent need to find alternatives to
conventional feed ingredients such as fishmeal and
soybean meal has led to the exploration of insect
protein as a nonconventional ingredient (Shah et al.,
2022; Amza et al., 2021; Azagoh et al., 2016; Van Huis et
al., 2013). Insects, with their rapid growth rate, efficient
food conversion, and minimal resource requirements,
have great potential for improving the sustainability of
intensive animal production systems (Imathiu, 2020).
They have been part of the natural diet of many
species, such as fish, birds, and pigs, and their use in
fish and poultry diets contributes to reducing feed costs,
producing biofertilizer from insect frass, and promoting social
inclusion (BarragánFonseca et al., 2020; BarragánFonseca et
al., 2022; Smith and Barnes, 2015; Szendrő et al., 2020).
Consumo de poliestireno expandido por Tenebrio molitor e Zophobas atratus e
utilização de seu farelo como ração para Piaractus brachypomus
Resumo. O poliestireno expandido (PS) representa um grande desafio para o gerenciamento ambiental devido aos
seus altos níveis de produção e ao gerenciamento insuficiente de resíduos. Entretanto, estudos recentes têm
demonstrado a capacidade do Tenebrio molitor e Zophobas atratus de biodegradar o PS, bem como a possibilidade de
utilizar a farinha dessas espécies para alimentar peixes. O objetivo deste estudo foi avaliar o efeito da inclusão de
farinha de insetos como substituto da farinha de peixe em dietas para alevinos de Piaractus brachypomus. O primeiro
experimento avaliou o efeito de 5 níveis de PS e farelo de trigo (WB) (100 % PS:0 % WB, 75 % PS:25 % WB, 50 %
PS:50 % WB, 25 % PS:75 % WB e 0 % PS:100 % WB) no crescimento e na composição das larvas de T. molitor e Z.
atratus. No segundo experimento foram avaliadas 10 dietas para alevinos de Piaractus brachypomus, sendo cinco
níveis (100, 75, 50, 25 e 0 %) de substituição da farinha de peixe de uma formulação dietética convencional por
farinha de T. molitor ou Z. atratus previamente alimentados com PS. No primeiro experimento, o melhor tratamento
para ambas as espécies foi 25 % PS:75 % WB, resultando na maior taxa de crescimento e consumo de PS. No
segundo experimento, não foram encontradas diferenças significativas entre os tratamentos para nenhuma das
variáveis avaliadas para o desempenho produtivo dos peixes. Concluímos que até 100 % da farinha de peixe na
dieta de alevinos de Piaractus brachypomus pode ser substituída por farinha de T. molitor ou Z. atratus alimentados
com PS. Não entanto, são necessários mais estudos sobre os efeitos ao longo prazo na saúde dos peixes e nos seres
humanos que os consomem.
Palavraschave: Peixe cachama, economia circular, larva de besouro (kingworm), larva de farinha (mealworm), plásticos
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
123
Polystyrene consumption by tenebrionid beetles for fish feed
Materials and Methods
Experiment 1. Consumption of PS by T. molitor and
Z. atratus
Experimental individuals
The larvae of T. molitor and Z. atratus were obtained
from a colony maintained under constant conditions
(LD 12:12 h photoperiod, 27±1 °C, 70 % relative
humidity) in the Center for Terrestrial Arthropod
Research of the National University of Colombia. The
experiment was carried out in the breeding room of the
Entomology Laboratory of the Institute of
Biotechnology of the National University of Colombia,
under environmental conditions controlled for ideal
development of the species (LD 8:16 h photoperiod,
28±2 °C, 75 % relative humidity), like those reported in
previous experiments (Yang et al., 2018).
Diets and experimental design
To evaluate consumption of PS, for each insect
species five diets (treatments) were formulated, which
varied in their ratio of polystyrene (PS) to wheat bran
(WB): 100 % PS:0 % WB, 75 % PS:25 % WB, 50 % PS:50
% WB, 25 % PS:75 % WB, and 0 % PS:100 % WB. WB
was selected as it is a source of B complex vitamins,
protein, amino acids, and trace minerals; it has been
shown to be a good substrate for breeding these
species (Gibson and Hunter, 2010; Vega and Dowd,
2005); and it has been suggested that it could optimize
biodegradation of PS by T. molitor larvae (Nukmal et
al., 2018). For the trial with each insect species each
treatment had six replicates (plastic recipient with 50
insect larvae) randomly assigned according to a
completely randomized design. The plastic recipient of
each experimental unit was 16 cm long by 11 cm wide
by 12 cm high in the case of T. molitor, and 20 cm long
by 15 cm wide by 12 cm high in the case of Z. atratus.
The larvae used was selected after 12 days of
development, in the case of T. molitor measuring 2.0
+/ 0.2 cm (instar 14), and for Z. atratus 3.0 +/ 0.2 cm
(instar 12). A prior experiment showed that PS
consumption by the larvae of both species was greater
when it was placed in the form of 5 +/ 1 mm thick
sheets and 0,5 weight, and therefore PS was provided
in this manner. At the start of the experiment, the
WB+PS was supplied for the duration of the
experiment to T. molitor and Z. atratus, consisting of 100
% of the initial weight of the experimental unit of the
50 individuals (Latney et al., 2017). The experiment
Several insect species have been demonstrated to
provide a viable source of protein for use as animal
feed. The meal of T. molitor and Z. atratus has a protein
content of approximately 4550 % DM. The larvae of T.
molitor may be incorporated live or in the form of meal
or oil in the feed of pets or livestock (Gasco et al., 2020;
Henry et al., 2015; Sogari et al., 2019). Additionally,
studies have established digestibility rates of 60–80 %
for crude protein of T. molitor (Kovitvadhi et al., 2019;
Mancini et al., 2021), and 77–92 % for Z. atratus (Bosch
et al., 2016; Kovitvadhi et al., 2019).
Studies have documented the feasibility of subs
tituting up to 25 % of fish meal with meal of T. molitor
in aquaculture production (Gasco et al., 2019). Feed
formulated for aquaculture species that contain T.
molitor as a principal ingredient has been demonstrated
to have beneficial effects on growth rates – and in turn
yield of a variety of commercially raised fish,
including rainbow trout (Oncorhynchus mykiss) (Jeong
et al., 2020; Melenchón et al., 2021), porgy (Sparus
aurata) (Fabrikov et al., 2020; Piccolo et al., 2017), tench
(Tinca tinca) (Fabrikov et al., 2020), European bass
(Dicentrarchus labrax) (Gasco et al., 2016; Mastoraki et
al., 2020), blackspot seabeam (Pagellus bogaraveo)
(Iaconisi et al., 2017), Nile tilapia (Oreochromis niloticus)
(SánchezMuros et al., 2016; Tubin et al., 2020), and
Pacific whiteleg shrimp (Litopenaeus vannamei) (Motte et
al., 2019; Panini et al., 2017). These studies have also
indicated that: 1) T. molitor improves the quality of the
meat; 2) insects in general are a potential source of
protein in the diet of fish; and 3) their inclusion may
contribute to developing circular economies (Moruzzo
et al., 2021) by degrading waste while producing high
quality protein at a low cost.
Using insects as alternative protein sources may also
have a positive impact on production of tropical
omnivorous freshwater species such as white cachama
(Piaractus brachypomus), which has great commercial
potential due to its adaptability to a variety of foods,
resistance to low oxygen levels, high productive
parameters, and high demand due to the colour and
flavour of its meat (Chirinos et al., 2022; Mesa and
BoteroAguirre, 2007; Ribeiro et al., 2016). For these
reasons, it is one of the most widely raised species in
Latin America, with a total yield in 2021 of 31,200 tons,
which continues to increase (Ministerio de Agricultura
y Desarrollo Rural, 2021).
The objective of this study was to evaluate the effect of
including insect meal as a substitute for fishmeal in diets
for Piaractus brachypomus fingerlings. This would allow for
contributing to development of circular economies in
agriculture involving consumption and degradation of PS
by insects to be used to feed fish for human consumption.
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
124
duration was 64 days for T. molitor and 32 days for Z.
atratus, with the disparity due to the extended life cycle
of each species, given that T. molitor has a longer larval
stage but they are larvae of lower weight and size.
while the Z. atratus larva develops more quickly,
generating a greater animal biomass in less time. For
each treatment, productive performance of the larvae
was evaluated based on the following variables: 1) total
final weight (g); 2) survival (# live larvae at end of
experiment ÷ # initial larvae x 100); and 3)
consumption of PS (weight in g of PS at beginning of
experiment – weight at end of experiment).
Proximate analysis of meal of larvae of T. molitor and
Z. atratus
The larvae of T. molitor and Z. atratus of the treatment
with the best productive performance after
consumption of PS +WB were ground into meal. A
protocol of elaboration of meal from each of the two
species was developed, which basically consisted of
fasting the larvae for 24 hours, then screening, washing
and sacrifice by freezing (< 18 °C 24h) were carried out,
followed by thawing for 1 hour at room temperature,
then blanching in water at 60 °C for 5 minutes. The
larvae were dehydrated at 60°C for 24 hours, and
ground until obtaining a fine and homogeneous
mixture, which formed the insect flour of each species.
Protocol adapted from MelgarLalanne et al. (2019) and
Arévalo Arévalo et al. (2022). At the Laboratory of
Animal Nutrition of the National University of
Colombia, a proximate analysis was carried out of the
meal of the larvae of each species, analysing the
following: dry matter, crude protein, crude fiber, ether
extract, gross energy, ash, calcium, and phosphorus
(Scientific Standards & Methods AOAC, 2023).
Experiment 2. Replacement of fish meal in the diet of
white cachama (Piaractus brachypomus) with meal of
T. molitor and Z. atratus previously fed with
polystyrene
Experimental individuals
Fingerlings of white cachama (Piaractus brachypomus)
employed in the experiments were obtained from the
company Aquaprimavera Ltda (Meta, Colombia). The
experimental phase was carried out in the bioterium of
the Corporation of Veterinary Pathology, where the
experimental individuals were submitted to a 15day
period of adaptation prior to the experiment in five 80
L plastic tanks, in accordance with maintenance
parameters for the species (VásquezTorres et al., 2011).
Experimental diets
A total of 10 experimental diets were formulated,
replacing 100, 75, 50, 25, or 0 % of the fish meal in their
dietary formulation with meal of T. molitor or Z. atratus
previously fed with PS, which corresponded to 10, 7.5,
5.0, 2.5, and 0 % of their total diet. The following
requirements for white cachama fingerlings were
fulfilled: crude protein 36 %, lipids 6 %, 4588 kcal/kg,
lysine 2.22 %, methionine 0.78 %, total phosphorous
1.39 %, digestible phosphorous 0.76 %, calcium 1.14 %,
linolenic acid (18:2n6) 0.8 %, and linolenic acid (18:3n
3) 0.2 % (Abdel et al., 2010; Gao et al., 2011; Vásquez
Torres and AriasCastellanos, 2012). The formulation
was developed using the Linear Program Solver by
Microsoft Excel
©
. The resulting diets were both
isoproteinic and isoenergetic (Table 1).
Experimental design
For the second experiment, 180 white cachama
fingerlings were used, with an average weight of 1.48 ±
0.14 g, distributed in 30 tanks (20L each; 6 fish/ tank; 3
tanks/ treatment). Each tank had a central aerator and
heating with an individual thermostat. The parameters
of water quality, temperature, pH, and dissolved
oxygen were recorded daily, and the parameters NO
2
,
NO
3
, and NH
4
were recorded weekly. Each tank was
cleaned daily by siphoning, replacing water lost
through cleaning or evaporation. Diets were randomly
assigned to the tanks and feed was supplied three times
daily (09:00 am, 11:30 am, and 3:00 pm) for 35 days,
providing 10 % of their weight in feed, according to the
formulation in Table 1. Total weight of the fish of each
tank was recorded weekly and amount of feed adjusted
correspondingly. Initial weight (IW, g), final weight
(FW, g), and feed consumption (FC, g/fish) were
determined weekly and used to calculate the following
variables: weight gain (WG, g) = FW–IW; feed
consumption per fish (FC, g/fish) = total consumption
per tank / final # fish in tank; specific growth rate (SGR
(% growth/day = (100*l [(lm FW) (ln FW] / (days of
experiment). The feed conversion rate was calculated
using the following formula: FCR = FC /WG. Rate of
survival (S) was calculated using the following formula:
S (%) = (final # fish / initial # fish) x 100.
Statistical analysis
Analysis of variance was carried out for data of both
experiments; for experiment 1, analysis was carried out
for each species using a completely random design,
and for experiment 2, a completely random design
with a 2 x 5 factorial arrangement was used, evaluating
meal of larvae of each insect species for each of the five
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
BonillaAmaya et al.
Ingredients (%) Tenebrio molitor Treatments Zophobas atratus Treatments
100%TM 75%TM 50%TM 25%TM 0%TM 100%ZA 75%ZA 50%ZA 25%ZA 0%ZA
Tenebrio molitor
meal 10 7.5 5 2.5 0 0 0 0 0 0
Zophobas atratus
meal 0 0 0 0 0 10 7.5 5 2.5 0
Soybean meal, 45%
CP, extracted with
solvent 25 25 25 25 25 25 25 25 25 25
Soy, whole,
extruded 10 10 10 10 10 10 10 10 10 10
Maize gluten
meal, 60 % CP 14.4 14.4 14.4 14.4 14.4 14.4 14.4 14.4 14.4 144
Yellow maize 27.2 27.2 27.2 27.2 27.2 27.2 27.2 27.2 27.2 27.2
Tuna fish meal,
manually extracted 0 2.5 5 7.5 10 0 2.5 5 7.5 10
Meat and bone
meal 50% 10 10 10 10 10 10 10 10 10 10
Canola oil 2 2 2 2 2 2 2 2 2 2
Salt .3 .3 .3 .3 .3 .3 .3 .3 .3 .3
Vitamin and
mineral premix .25 .25 .25 .25 .25 .25 .25 .25 .25 .25
Antioxidant 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013
Rovimixstay
C 35, ascorbic
monophosphate 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045 0.045
LLysine HCL 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61
Threonine 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
Choline Chloride (60 %) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Parameters analyzed (%)
Humidity 8.9 9.2 9.4 9.2 9.4 8.9 9.1 9.4 9.9 9.6
Dry matter 91.1 90.8 90.6 90.8 90.6 91.1 90.9 90.6 90.1 90.4
Crude protein
(Nx6.25) 36.0 35.8 36.8 36.8 36.7 35.7 35.4 36.6 36.1 36.6
Crude fiber 1.5 1.3 1.4 1.4 1.3 1.3 1.2 1.2 1 1.4
Ether extract 7.7 8.6 7.8 9.3 7.8 10 9.6 8 8.3 7.4
Ash 5.4 5.6 5.9 6.3 6.6 5.4 5.6 6.0 6.3 6.9
Nonnitrogenated
extract
2
43.5 39.5 38.7 37.0 38.2 38.7 39.1 38.8 38.4 38.1
Calcium 1.6 1.7 1.7 1.8 1.9 1.5 1.4 1.7 1.7 2
125
for each species using a completely random design,
and for experiment 2, a completely random design
with a 2 x 5 factorial arrangement was used, evaluating
meal of larvae of each insect species for each of the five
levels of inclusion of PS. In each analysis, assumptions
of homogeneity of variances were verified through the
Levene test, and normality of errors was verified
through the ShapiroWilks test. For separation of
means, the Tukey test was employed. For all statistical
tests, the level of significance was 5 %. For experiment 1,
regression models were used to describe degradation of
PS in function of the level of inclusion of PS. All analyses
were carried out using the R program (The R Project for
Statistical Computing, 2021) .
Table 1. Experimental diets for white cachama (Piaractus brachypomus), fully or partially replacing fish meal with meal of T.
molitor (TM) and Z. atratus (ZA) fed with polystyrene
1
1
AOAC 1996. Official Methods of Analysis of the Association of Analytical Chemists
2
Nonnitrogenated extract (%) = Dry matter – Crude protein – Crude fibre – Ether extract – Ash
Results
Experiment 1
PS consumption by T. molitor and Z. atratus
In the case of T. molitor, given varying initial larval
weights, initial weight served as a covariate for weight
related analyses. Significance (P < 0.05) was observed
only for final weight and total consumption, both
showing positive covariate estimates, indicating higher
values with increased initial weight at 60 days. The
covariate persisted for all variables, and adjusted
means were based on the mean initial weight (3.02 g/
50 larvae). PS inclusion significantly (P < 0.05) affected
total consumption and biodegradation percentage,
generally resulting in lower values with increased PS
levels (Table 2).
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
Polystyrene consumption by tenebrionid beetles for fish feed
126
Table 2. Least squares method for the effect of different levels of PS inclusion on the performance of Tenebrio molitor larvae during
a 32day experiment (n=6). The initial weight was included as a covariate
Treatment Initial weight Final weight Weight gain Total consumption BD of PS
(g/50 larvae) (g/50 larvae) (g/50 larvae) (g/50larvae) (%)
100% PS:0%WB 3.13
a
4.37 1.35 0.45
e
17.67
b
75% PS:25% WB 3.05
ab
4.39 1.37 1.14
d
17.81
b
50% PS:50% WB 3.05
ab
4.46 1.50 1.90
c
26.34
b
25% PS:75% WB 3.05
ab
4.52 1.61 2.67
b
53.77
a
0% PS:100% WB 2.89
b
4.63 1.44 3.00
a
NA
EE 0.05 0.10 0.10 0.03 2.28
Pvalue 0.016 0.405 0.265 0.000 0.000
Pvalor PI* 0.041 0.738 0.000 0.896
WB: wheat bran; PS: expanded polystyrene (styrofoam); SE: standard error of the means; BD: biodegradation; NA: not applicable.
Different letters in the same column indicate significant differences as a result of the Tukey test (P<0.05). *Pvalue for the effect of the
covariate initial weight.
The percentage of degradation of PS (Y) in function
of level of inclusion of PS (X) was described using the
Weibull function, resulting in the following equation: Y
= 100 – (83.1183.10*exp(0.0076X
1.448
)) (P > 0.05; R
2
=
0.98; SE = 4). Quantity of PS degraded (QPSD),
expressed as g / 100 g of substrate (PS + WB) was
calculated by simulating QPSD = degradation PS (%)*
Inclusion PS (%)/100, in function of the level of
inclusion of PS. This indicates a growing tendency
toward an initial maximum value of 14.1 g for a level of
inclusion of 32 % with a level of degradation of PS of
44.05 % (14.1g); this level of degradation was achieved
with inclusion of PS of 76 % and degradation of 18.6 %
(14.1g) (Figure 1).
Figure 1. Regression model of the quantity of polystyrene (PS) biodegraded (g) by
larvae of T. molitor in function of the level of inclusion of PS in their diet.
In the case of Z. atratus, increase in level of inclusion of
PS reduced weight gain, total consumption of substrate
(PS + WB), and degradation of PS (P < 0.05; Table 3).
Decrease in the percentage of degradation of PS (Y)
in function of the level of inclusion of PS (X) was
described through a Weibull thirddegree polynomial,
obtaining the following equation: Y = 32.68
1.433*X+0.0246*X
2
0.000132*X
3
(P < 0.05, R
2
= 0.75; SE =
1.49). The quantity of PS degraded expressed in g/100
g of substrate (PS + WB) was calculated as QPSD =
Degradation PS (%) * Inclusion PS (%) /100 was
simulated as function of the level of inclusion of PS.
This indicates a growing tendency toward a maximum
value of 6.4 g, with a level of inclusion of 48, and a
level of degradation of 7.61 %. However, a peak value
of 2.56 g was observed at an inclusion level of 21 %,
accompanied by a 12.2 % degradation of PS (Figure 2).
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
BonillaAmaya et al.
127
Table 3. Effect of different levels of inclusion of polystyrene in the diet on productive performance of larvae of Zophobas atratus
during a 30day experiment
Treatment Initial weight Final weight Weight gain Total consumption BD of PS
(g/50 larvae) (g/50 larvae) (g/50 larvae) (g/50 larvae) (%)
100% PS: 0% WB 2.08 2.75
b
0.67
bc
0.08
e
3.76
c
75% PS:25% WB 2.08 2.70
b
0.63
c
0.65
d
8.05
ab
50% PS:50% WB 2.09 2.71
b
0.62
c
1.11
c
6.08
bc
25% PS:75% WB 2.12 2.92
a
0.80
ab
1.68
b
10.17
a
0% PS:100% WB 2.13 2.95
a
0.82
a
2.13
a
NA
SE 0.01 0.03 0.04 0.01 0.62
P value 0.062 0.000 0.001 0.000 0.000
WB: wheat bran; PS: expanded polystyrene (styrofoam); SE: standard error of the means; BD biodegradation; NA: not applicable.
Different letters in the same column indicate significant differences as a result of the Tukey test (P < 0.05).
Figure 2. Regression model of the quantity of polystyrene (PS) biodegraded (g) by
larvae of Z. atratus in function of the level of inclusion of PS in their diet.
Results allow for concluding that the best treatment
for each of the two insect species was 25 % PS:75 % WB,
which optimized growth and consumption of PS.
Proximate analysis of T. molitor and Z. atratus meal
Table 4 shows the results of the proximate analysis
carried out of the meal of T. molitor and Z. atratus
larvae fed with that treatment of experiment 1 which
resulted in optimal insect growth and consumption of
PS: 25 % PS:75 % WB.
Table 3. Effect of different levels of inclusion of polystyrene
in the diet on productive performance of larvae of Zophobas
atratus during a 30day experiment
Parameter T. molitor Z. atratus
Moisture (%) 11.1 9.9
Dry matter (%) 88.9 90.1
Crude protein (Nx6.25)
1
51.0 42.6
Crude fiber
1
(%) 6.1 4.6
Ether extract
1
(%) 25.6 36.2
Ash
1
(%) 3.5 2.2
Nonnitrogenated extract (%) 2.8 4.5
Calcium
1
(%) 0.06 0.05
1
Scientific Standards & Methods AOAC, 1996
Experiment 2
Replacement of fish meal with meal of T. molitor
and Z. atratus fed with PS in diets of white
cachama (Piaractus brachypomus)
In terms of productive parameters, no significant
differences were observed (p > 0.05) among
treatments for all the studied variables; rather, P.
brachypomus fed with ten diets with different levels
of inclusion of T. molitor and Z. atratus in turn fed
with PS showed equal productive performance.
Table 5 shows average values and standard
deviation calculated for performance of P.
brachypomus fingerlings. Survival of 100% of the fish
was recorded for all treatments.
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Polystyrene consumption by tenebrionid beetles for fish feed
128
Table 5. Average values (±SD) of productive variables* for white cachama (Piaractus brachypomus) fed with diets including meal
of T. molitor (TM) or Z. atratus (ZA), in turn fed with polystyrene
Experimental Diet IW (g/fish) FW (g/fish) WG (g/fish) SGR (%/day) FC (g/fish) FCR
100% TM 1.54 (0.08) 9.77 (1.68) 8.23 (1.76) 525 (064) 12.83 (0.93) 1.59 (0.22)
75% TM 1.46 (0.07) 9.53 (0.52) 8.06 (0.58) 5.35 (0.28) 13.09 (0.52) 1.63 (0.12)
50% TM 1.49 (0.16) 10.24 (2.15) 8.75 (2.23) 5.48 (0.77) 12.87 (0.84) 1.52 (0.27)
25% TM 1.54 (0.20) 11.19 (0.91) 9.64 (0.93) 5.67 (0.45) 13.84 (0.90) 1.44 (0.09)
0% TM 1.55 (0.08) 10.33 (0.74) 8.79 (0.79) 5.43 (0.33) 13.63 (0.66) 1.56 (0.18)
100% ZA 1.36 (0.03) 9.10 (0.71) 7.74 (0.71) 5.42 (0.23) 12.32 (0.65) 1.59 (0.07)
75% ZA 1.49 (0.04) 11.20 (1.03) 9.71 (1.00) 5.75 (0.22) 13.98 (0.57) 1.45 (0.15)
50% ZA 1.48 (0.04) 10.42 (0.92) 8.94 (0.94) 5.57 (0.30) 13.82 (0.30) 1.56 (0.14)
25% ZA 1.56 (0.09) 10.91 (0.80) 9.34 (0.90) 5.55 (0.38) 13.87 (0.09) 1.49 (0.15)
0% ZA 1.47 (0.14) 10.22 (2.18) 8.75 (2.05) 5.52 (0.35) 13.83 (2.08) 1.60 (0.13)
PValue
Inclusion of insect meal 0.5969
ns
0.3561
ns
0.4285
ns
0.8338
ns
0.1566
ns
0.6940
ns
Species 0.2973
ns
0.7437
ns
0.6762
ns
0.4285
ns
0.3582
ns
0.8944
ns
Inclusion of Insect meal
x species 0.4293
ns
0.5874
ns
0.6491
ns
0.8844
ns
0.6074
ns
0.6941
ns
ns
nonsignificant differences (P > 0.05)
*Productive variables measured: Initial weight (IW), Final weight (FW); Weight gain (WG) = FW – IW; Specific growth rate (SGR) = 100* [(ln FW) (ln FW)] / (days
of experiment); Feed consumption per fish (FC) = total consumption per tank / final number of fish in tank; Feed conversion rate (FCR) = FC / WG
Consumption of PS by T. molitor and Z. atratus
The larvae of both T. molitor and Z. atratus were
observed to be capable of consuming PS; for both
species, in each treatment in which sheets of PS were
placed, the larvae consumed the PS, as evidenced by
orifices and loss of volume of PS. This was
corroborated by data obtained for weight of PS
remaining at the end of the experiment, as well as
weight gain of individuals upon consumption of
different proportions of PS and WB. These results
indicate that larvae of T. molitor may reduce the
volume of PS supplied by 10 to 65 % in 64 days, and
larvae of Z. atratus may reduce PS by 3 to 12 % in 32
days (in accordance with the different life cycles of the
two species). Larvae fed with a combination of PS and
WB consumed more PS than those fed only with PS.
For both insect species, the diet of 25 % PS:75 % WB
resulted in the greatest level of PS consumption and
thus the greatest percentage of biodegradation of PS,
which may indicate that provision of WB contributed
to increased consumption – and optimized
biodegradation – of PS by the larvae, as has been
suggested for T. molitor (Yang et al., 2018).
Additionally, as a nutritional adjuvant, WB contributed
to weight gain of individuals, principally for Z. atratus.
Previous studies have found greater increase in
weight of the larvae and proportionally the process of
biodegradation in treatments containing both plastic
and natural feed such as wheat bran (Brandon et al.,
2018; Nukmal et al., 2018; Yang et al., 2018).This
concords with the findings of the present study, which
indicated that the best treatments were those
containing 25 % PS and 75 % WB, the latter of which
provides nutrients and has been proven to be a good
substrate for breeding the species included in the
present study and to foment biodegradation of PS by
Z. atratus larvae (Nukmal et al., 2018). Similarly, use of
wheat bran was found to contribute to biodegradation
of PS by the larvae in the present study. Due to their
greater size, the larvae of Z. atratus showed greater
consumption of PS than those of T. molitor. The
differences between these species could also be
associated with differences in their genetic traits and
their intestinal microbial communities. Additional
studies are necessary to address the mechanisms of
degradation of PS in relation to the insects` digestive
enzymes, the insect and microbial genes, and the
natural dietary behaviors of T. molitor and Z. atratus.
It is noteworthy that although the rates of
consumption of PS and weight gain of T. molitor and Z.
atratus in those treatments with 100 % PS were lower
than those fed with treatments including WB, the
individuals increased in size as well as weight. This
indicates that the larvae did assimilate some energy
upon biodegrading PS. Thus, for all five treatments
evaluated, the larvae of both species increased in
weight while reducing the weight of PS, and survival
was high in all treatments, which concords with Wang
et al. (2022), who reported that these species may
survive with solely plastic diets, although a decrease
occurred in weight of the individuals after 20 days fed
Discussion
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BonillaAmaya et al.
129
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (2): 6975
with this diet. Effectively, while larvae of T. molitor and
Z. atratus may degrade these materials, they do not
provide them with an efficient energy source to
complete their life cycle, but rather merely allow them
to survive (Kooijman, 2009; Wu et al., 2019).
Results of the nutritional analysis of the meals
obtained from the T. molitor and Z. atratus larvae fed
with the diet that resulted in the highest yield (25 %
PS:75 % WB) were similar to those reported by other
authors for these species (Basto et al., 2020; Benzertiha
et al., 2019; Fontes et al., 2019; Gasco et al., 2016; Kulma
et al., 2020; Soares et al., 2019; Zielińska et al., 2021).
Protein is a principal nutritional component of insects
used as animal feed, although protein content varies
among species. Adults and larvae of the order
Coleoptera have a protein content of 2071 % (Sánchez
Muros et al., 2014). In the present study, the crude
protein content obtained for T. molitor and Z. atratus
fed with PS was 51 and 42.6 %, respectively, which is
similar to those reported by other authors for meals of
these species. This demonstrates their high protein
content and their potential value as nonconventional
sources of protein for feeding fish and livestock (De
Marco et al., 2015). The present study obtained a crude
fat content of 25.6 % for T. molitor and 36.2 % for Z.
atratus, similar to those reported by other authors,
indicating that the larvae of these insect species possess
a high level of fat compared to other potential
ingredients in animal feed. Tenebrio larvae have a high
level of unsaturated fatty acids, corresponding to close
to 80 % of their total fat, principally consisting of
monounsaturated oleic acid and polyunsaturated
linoleic acid (Valdez and Untiveros, 2010). This high fat
content directly affects production of meal; compared
to ingredients typically used in feed, Tenebrio meal has
a greater level of clumping, is courser, and has a
shorter shelf life, suggesting that oxidation of the lipid
fraction of insects may be responsible for it easily
becoming rancid (Ribeiro et al., 2019). This high fat
content may provide energy when used in feed, but
may also be a limiting factor as it may become rancid
when using the live or complete larvae. The Ca content
in larvae and in insects in general is relatively low due
to the fact that the majority of insects do not possess an
internal skeleton (Nowak et al., 2016). In the meals of the
larvae of T. molitor and Z. atratus, Ca as well as P are low
and should be taken into account upon balancing the
rations for species that require high levels of Ca.
The experiment corroborated that the larvae of T.
molitor and Z. atratus may provide an option for
biodegrading PS, as they may consume PS and gain
weight, independently of the nutritional adjuvant.
However, it is clear that an adjuvant such as wheat
bran may improve the efficiency of the biodegradation
process, which may facilitate standardization of PS
degradation on a medium or large scale. There is a
need for additional studies of different adjuvants,
including organic waste, that may contribute to
efficiency of biodegradation in industrial insect
production. With respect to the nutritional content of
meals obtained from T. molitor and Z. atratus, this study
showed values of dry matter, crude protein, and crude
fibre similar to those reported by other authors,
demonstrating that the larvae of these insect species,
aside from being capable of biodegrading PS, may be a
viable food source for animals and humans.
Nevertheless, it is necessary to evaluate their safety for
animal and human consumption, especially regarding
presence of microplastics and toxic residues resulting
from biodegradation of plastics, which may
accumulate in the insects` biomass.
Replacement of fish meal with T. molitor and Z.
atratus meal in the diet of white cachama (Piaractus
brachypomus)
The results of the present study for productive
performance of P. brachypomus fingerlings fed with the
10 experimental diets indicate that up to 100 % of the
fish meal in dietary formulations for commercial fish
production – or 10 % of the total diet may be replaced
with full fat meal of larvae of T. molitor or Z. atratus
without negatively affecting their productive
performance or survival. This allows for formulating
isonitrogenated diets without having to modify
ingredients of conventional dietary formulations other
than fish meal. Thus, variations observed in content of
ether extract and raw energy among the different
treatments as a result of the proportion of these
nutrients in the total insect meal provided did not
affect the parameters studied.
P. brachypomus is omnivorous, and in its natural
environment its feeding habits vary according to the
food resources available in the rivers it inhabits.
Although the majority of studies have been carried out
on carnivorous species, principally with protein of T.
molitor, a recent study (Couto et al., 2021) evaluated
substitution of 10, 20, and 30 % of commercial feed
concentrate with T. molitor meal in the diet of P.
brachypomus fingerlings, finding the parameters of
weight increase, total average growth, survival rate (57
%), feed conversion index, and the total productivity
index similar to those of the control only in the case of
10 % replacement, while for 20 and 30 % replacement,
yield of the fish decreased. A tendency toward weight
loss in fish fed with diets with a high lipid content has
been observed for P. brachypomus as well as other
Polystyrene consumption by tenebrionid beetles for fish feed
130
species. For example, for the red drum (Sciaenops
ocellatus), upon comparing diets with 4, 7, 14, and 21 % of
lipids, less growth was observed in those fed diets with
the higher lipid contents (14 and 21 %) (Craig et al., 1999).
In their natural environment, P. brachypomus
consumes seeds and fruits with high levels of
carbohydrates, and uses carbohydrates as an energy
source with greater efficiency than it does lipids
(VásquezTorres et al. 2011). For example, a study of
juvenile P. brachypomus evaluating nine commercial
type isoproteinic diets (all with a protein content of 32
%) with different levels of carbohydrates (20, 28, and 36
%) and lipids (4, 8, and 12 %) indicated a clear
tendency of reduction in weight gain of fish as the
levels of lipids increased (VásquezTorrres and Arias
Castellanos, 2012). It appears that reduction in lipids in
diets with a high carbohydrate content increases
weight gain of fish. Similar results have been reported
for fingerlings of Nile tilapia (Oreochromis niloticus), in
which replacement of up to 50 % of fish meal with T.
molitor meal did not affect the quantity of feed
consumed, but negatively affected growth of the fish
(SánchezMuros et al., 2016).
Such results of replacement of T. molitor meal may
adversely affect productive parameters, whether due to
the high fat content or the content of chitin, a polymer
found in the exoskeleton of insects. For example, a study
of tilapia (Oreochromis niloticus) suggests that
consumption of chitin may reduce the efficiency of
enzymes that break down nutrients in food, impeding full
absorption of proteins and lipids by the gastrointestinal
tract (Fontes, 2018). However, Henry et al. (2015) suggest
that low productive indices in fish consuming insects may
be attributed to a lack of certain amino acids in the
protein of some insect species consumed, which could be
avoided by combining different protein sources or
supplementing with amino acids.
It has also been reported that different levels of
inclusion of T. molitor meal may have positive effects
on several species de fish. For example, for juvenile
rainbow trout (Oncorhynchus mykiss), upon partially
replacing (0, 33 and 66 %) of fish meal in dietary
formulations with T. molitor meal (0, 25, and 50 % of the
total diet), there were no differences in weight gain of
the fish, or in the physical characteristics of the raw or
cooked fillets (Iaconisi et al., 2018). Furthermore,
replacement of 0, 25, 50, and 75 % of fishmeal with T.
molitor meal in dietary formulations of yellow catfish
(Pelteobagrus fulvidraco; 0, 9, 18, and 27 % of the total
diet) did not result in significant differences in feeding
rate, specific growth rate, or feed conversion efficiency
(Su et al., 2017). Similarly, upon replacing 0, 35, and 71
% of fish meal with T. molitor meal in diets for gilthead
seabeam (Sparus aurata; 0, 25, and 50 % of the total
diet), it was found that up to 35 % of fish meal may be
replaced by T. molitor meal without negative effects on
weight gain (Piccolo et al., 2017). For fingerlings of the
hybrid giant tiger grouper (Epinephelus lanceolatus x
Epinephelus fuscoguttatus), Song et al. (2018) studied six
diets, all of which were isonitrogenated and isolipidic,
replacing 0, 6.25, 12.5, 18.75, 25, and 31.25 % of fish meal
with T. molitor meal, finding the greatest growth rate with
12.5 % (4.92 % of the total diet) replacement of fish meal.
Several authors have evaluated inclusion of full fat,
degreased, and hydrolyzed Z. atratus meal in diets for
diverse species de fish. Nevertheless, no records exist
of its use to feed P. brachypomus. For lubina
(Dicentrarchus labrax) in aquaentoponic systems using
insects as feed, Stathopoulou et al., (2022) recently
evaluated substitution of 10 % and 20 % of fish meal
with defatted Zophobas meal, and Prachom et al. (2021)
11.1 to 44.4 % of fish meal with degreased meal of
larvae of Z. atratus in a study feeding barramundi fish
(Lates carcarifer). Both studies established that no
significant differences exist among different rates of
replacement of fish meal with insect meal in volume
consumed, weight gain, final weight, feed conversion
index, specific growth weight, or survival of
individuals. Thus, we conclude that 10 %
(Stathopoulou et al., 2022) to 12 % (Prachom et al., 2021)
of the total diet may consist of degreased Z. atratus
meal without negative effects on the productive
performance of the fish.
Similar studies with hydrolyzed Z. atratus or T.
molitor meal as a substitute for 40 % of fish meal in
diets of juvenile brown trout (Salmo trutta) found no
differences in parameters of growth, volume of feed
consumed, or intestinal histomorphology (Mikołajczak
et al., 2020). In a study by Doğankaya (2016) of rainbow
trout (Oncorhynchus mykiss) in which 0, 25, 50, and 100
% of fish meal was replaced with Z. atratus meal, the
best performance was found replacing 25 %, which was
similar to the control treatment using commercial feed.
Another study established replacing up to 25 % of fish
meal in the diet of juvenile Nile tilapia (Oreochromis
niloticus) with Z. atratus meal did not present any
adverse effect on the productive parameters or body
composition of the fish (Jabir et al., 2012). Similar
results were found in the diets of cobia (Rachycentron
canadum) upon replacing up to 30 % of fish meal with
Z. atratus meal, without significant effects on growth
among treatments, final average weight of the fish, or
the feed conversion index (Chainark et al., 2022).
ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 32 (3): 121 136
BonillaAmaya et al.
131
As observed in this study, in accordance with the
results of other studies using these insect species as
feed for different freshwater fish, it is possible to
partially replace fish meal with T. molitor or Z. atratus
meal without affecting the productive performance of
the fish (Abdel et al., 2010; Henry et al., 2018). There is
a need to evaluate replacement of greater levels of fish
meal with other foods with a nutritional content
similar to these insect meals, such as whole soybeans,
soybean meal, and other protein sources used in the
animal feed industry; to evaluate differences in
productive performance upon using whole, degreased,
vs. hydrolyzed insect meal; and to evaluate diets free of
fish meal. Although this study found no differences
among the various treatments of insect meal and fish
meal on productive performance of the fish, it is
important to evaluate use of different percentages of
inclusion of the meal of insects that have consumed PS
or other types of plastic, including over a greater time
in the productive cycle of the fish, in order to observe
any possible changes over time in productive
performance or health problems. Evaluation of the
hepatosomatic index (HSI) and viscerosomatic index
(VSI) is necessary to determine the effect of insect meal
on the fish`s metabolism, for example with respect to
synthesis and secretion of digestive enzymes, digestion
and absorption of food, and metabolism of
carbohydrates (Gümüş and İkiz, 2009).
Conclusions
Authors' Ethical Animal Welfare Declaration: The authors declare that the experimental procedures were executed
in accordance with the accepted principles of animal welfare in experimental science. These procedures were
conducted only after the experimental protocols received approval from the Bioethics Committee of the Faculty of
Veterinary Medicine and Animal Sciences at Universidad Nacional de Colombia.
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