Influences of a polystyrene diet on the growth and development of Tenebrio molitor
Department of Biological Sciences, U 6 Wallys Walk 110 Science Lab, Macquarie University
NSW 2109
Introduction
Plastic, a non-biodegradable waste which infects all ecosystems, presents among one of the
core influences of pollution throughout Earth. Since 2018, 380 million tonnes of plastic are
produced globally each year. Polystyrene (PS) is amongst one of the leading plastics towards
landfill, (Ritchie Roser 2018) occupying 240,000m3 of landfill space in NSW alone each
year (NSW EPA 2019). PS is utilized due to inexpensive manufacturing prices and practical
uses in everyday life (food packaging, building insulation). PS is a synthetic, hydrophobic
polymer with a high molecular mass, created by the polymerization of styrene, taking over
one million years to biodegrade (Chemical Safety Facts 2021). However, through the close
examination of the yellow mealworm larvae, Tenebrio molitor (species of darkling beetle),
this species developed the capability to increase plastic decomposition rates whilst
simultaneously gaining a higher proportion of adaptions to endure threatening environments
(Nylin & Gotthard 1998). In 2015, it was discovered this mealworm species gut bacteria
(Exiguobacterium sp. Strain YT2) displayed the ability to digest Styrofoam (a common PS)
within a period of <24 hours (Bozek et al. 2017), equivalent to the digestion period of their
natural diet (Yang et al. 2015). This species develops four life stages within their cycle: egg,
larva, pupa and adult (Yang et al. 2018), maturing and reproducing rapidly, providing a
suitable experiment for evolution and the effects of artificial selection. If mealworms can
maintain optimum nutrition on a PS diet and continue onto the reproductive phase, it may
provide a long-term solution regarding plastic waste. The experiment aimed to simulate an
experimental evolution approach by observing the effect of a complete PS diet in-contrast to a
nutritious wheat-germ (WG) diet, determining the natural response (growth and development)
of the mealworm Tenebrio molitor to change in an environment. Will the experiment reveal
plastic digestion capabilities in mealworms? Will a diet consisting solely of PS have a slight
negative effect on mealworms? Hypothesising that the mealworms survival decreases with the
consumption of a 100% PS diet, due to not meeting the required nutrition levels, entering an
energy preservation state. Consequently, hindering optimal growth, resulting in a smaller
average mass while enhancing mortality rate. Further, mealworms on the 50:50 diet (PS and
WG) will mature slower in contrast to the 100% WG fed mealworms, developing faster with
the lowest mortality rate.
, Method
With each individual wearing PPE attire (vinyl gloves, face mask), split into separate groups
of 2 individuals, 492 Tenebrio molitor mealworm larvae were acquired, 3 larvae in every
group (supplied by Department of Biological Sciences). Mass of each larvae identified on a
digital sartorius scale and recorded. Each larvae placed into 3 separate plastic cylinder tubes,
individually labelled to allow for accurate observation of each group. To obtain reliable
analytical results, food amounts were measured for each tube using a plastic measuring
cylinder; 1. 100% WG (10ml), 2. 50:50 WG:shredded PS (5ml each), and 3. 100% shredded
PS (10ml), each hydrated with 3 drops of distilled water from a pipette. Each tube positioned
in a room temperature environment (approximately 22.5C), with 50-60% humidity and
regular day/night light cycle for optimal activity. Once a week, water was added, remaining
food and organic waste separated by the Biological Department creating a controlled, stable
environment. Further, the cohort weighed and recorded surviving mealworms, placing them
back into their respective tubes, with an identical volume of food and water. Deceased worms
(rigid body, black coloration) recorded and disposed of. After 5 weeks, each group exchanged
mealworms (blind measuring to avoid unconscious bias) noting their lifecycle stage, mass and
survival. All data transferred into Excel on Biological Departments computer for analysing.
Results:
Larvae consuming a diet of 100% PS averaged the lowest final mass of 0.2280g, with 100%
WG diet average mass 0.2284g, indicating only slight variation (0.00036g difference) (Fig
#1). However, the 50:50 WG:PS diet mealworms obtained the greatest average mass
(0.2505g), (Fig #1) (One-way ANOVA: F = 7.19, df = 2, P = 0.009586). This correlates to the
developmental stages from larvae to pupae within the 50/50 diet as a positive developmental
rate was observed (63 pupae) (Fig #3). Again, with the 100% PS diet presenting the lowest
developmental rates (56 pupae), even with highest number of larvae (84). Evident within the
three groups, 100% WG diet obtained the highest count maturing to pupae stage (82) (Fig #3).
Further, adult/pupae’s highest average mass observed in 50/50 diet (0.2210g) (Fig #2).
Variation in average mass, represented through the 100% PS diet (0.2109g) and 100% WG
diet (0.2168g) (0.0059g difference) was much greater than larvae variation. Consequently,
though the 50/50 diet represented a positive effect correlating to pupae/adult average mass, it
does not display equal effect for rate of development (Fig #3) (One-way ANOVA: F =1.35, df
= 2, P = 0.262099). Represented as mealworms consuming a 100% WG diet obtained the
highest number of adults (35) lowest deaths (4), with the lowest count of larvae (43), doubling
the number of adults in 50/50 diet (14), and 4 times more adults in 100% PS diet (8) (Fig #3).
Department of Biological Sciences, U 6 Wallys Walk 110 Science Lab, Macquarie University
NSW 2109
Introduction
Plastic, a non-biodegradable waste which infects all ecosystems, presents among one of the
core influences of pollution throughout Earth. Since 2018, 380 million tonnes of plastic are
produced globally each year. Polystyrene (PS) is amongst one of the leading plastics towards
landfill, (Ritchie Roser 2018) occupying 240,000m3 of landfill space in NSW alone each
year (NSW EPA 2019). PS is utilized due to inexpensive manufacturing prices and practical
uses in everyday life (food packaging, building insulation). PS is a synthetic, hydrophobic
polymer with a high molecular mass, created by the polymerization of styrene, taking over
one million years to biodegrade (Chemical Safety Facts 2021). However, through the close
examination of the yellow mealworm larvae, Tenebrio molitor (species of darkling beetle),
this species developed the capability to increase plastic decomposition rates whilst
simultaneously gaining a higher proportion of adaptions to endure threatening environments
(Nylin & Gotthard 1998). In 2015, it was discovered this mealworm species gut bacteria
(Exiguobacterium sp. Strain YT2) displayed the ability to digest Styrofoam (a common PS)
within a period of <24 hours (Bozek et al. 2017), equivalent to the digestion period of their
natural diet (Yang et al. 2015). This species develops four life stages within their cycle: egg,
larva, pupa and adult (Yang et al. 2018), maturing and reproducing rapidly, providing a
suitable experiment for evolution and the effects of artificial selection. If mealworms can
maintain optimum nutrition on a PS diet and continue onto the reproductive phase, it may
provide a long-term solution regarding plastic waste. The experiment aimed to simulate an
experimental evolution approach by observing the effect of a complete PS diet in-contrast to a
nutritious wheat-germ (WG) diet, determining the natural response (growth and development)
of the mealworm Tenebrio molitor to change in an environment. Will the experiment reveal
plastic digestion capabilities in mealworms? Will a diet consisting solely of PS have a slight
negative effect on mealworms? Hypothesising that the mealworms survival decreases with the
consumption of a 100% PS diet, due to not meeting the required nutrition levels, entering an
energy preservation state. Consequently, hindering optimal growth, resulting in a smaller
average mass while enhancing mortality rate. Further, mealworms on the 50:50 diet (PS and
WG) will mature slower in contrast to the 100% WG fed mealworms, developing faster with
the lowest mortality rate.
, Method
With each individual wearing PPE attire (vinyl gloves, face mask), split into separate groups
of 2 individuals, 492 Tenebrio molitor mealworm larvae were acquired, 3 larvae in every
group (supplied by Department of Biological Sciences). Mass of each larvae identified on a
digital sartorius scale and recorded. Each larvae placed into 3 separate plastic cylinder tubes,
individually labelled to allow for accurate observation of each group. To obtain reliable
analytical results, food amounts were measured for each tube using a plastic measuring
cylinder; 1. 100% WG (10ml), 2. 50:50 WG:shredded PS (5ml each), and 3. 100% shredded
PS (10ml), each hydrated with 3 drops of distilled water from a pipette. Each tube positioned
in a room temperature environment (approximately 22.5C), with 50-60% humidity and
regular day/night light cycle for optimal activity. Once a week, water was added, remaining
food and organic waste separated by the Biological Department creating a controlled, stable
environment. Further, the cohort weighed and recorded surviving mealworms, placing them
back into their respective tubes, with an identical volume of food and water. Deceased worms
(rigid body, black coloration) recorded and disposed of. After 5 weeks, each group exchanged
mealworms (blind measuring to avoid unconscious bias) noting their lifecycle stage, mass and
survival. All data transferred into Excel on Biological Departments computer for analysing.
Results:
Larvae consuming a diet of 100% PS averaged the lowest final mass of 0.2280g, with 100%
WG diet average mass 0.2284g, indicating only slight variation (0.00036g difference) (Fig
#1). However, the 50:50 WG:PS diet mealworms obtained the greatest average mass
(0.2505g), (Fig #1) (One-way ANOVA: F = 7.19, df = 2, P = 0.009586). This correlates to the
developmental stages from larvae to pupae within the 50/50 diet as a positive developmental
rate was observed (63 pupae) (Fig #3). Again, with the 100% PS diet presenting the lowest
developmental rates (56 pupae), even with highest number of larvae (84). Evident within the
three groups, 100% WG diet obtained the highest count maturing to pupae stage (82) (Fig #3).
Further, adult/pupae’s highest average mass observed in 50/50 diet (0.2210g) (Fig #2).
Variation in average mass, represented through the 100% PS diet (0.2109g) and 100% WG
diet (0.2168g) (0.0059g difference) was much greater than larvae variation. Consequently,
though the 50/50 diet represented a positive effect correlating to pupae/adult average mass, it
does not display equal effect for rate of development (Fig #3) (One-way ANOVA: F =1.35, df
= 2, P = 0.262099). Represented as mealworms consuming a 100% WG diet obtained the
highest number of adults (35) lowest deaths (4), with the lowest count of larvae (43), doubling
the number of adults in 50/50 diet (14), and 4 times more adults in 100% PS diet (8) (Fig #3).
