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Biodegradation of Expanded Polystyrene by Larval and Adult Stages of Tenebrio molitor with Varying Substrates and Beddings
Summary
Mealworm larvae consumed and biodegraded expanded polystyrene roughly 50 times faster than adult beetles, with pre-treating EPS with lemon-lime soda increasing biodegradation rates by 482% and supplemental spinach increasing rates by 125%. These findings advance the prospect of using insect gut bacteria as a scalable biological tool for breaking down polystyrene, one of the most persistent and environmentally prevalent microplastic precursors.
Tenebrio molitor, a species of darkling beetle, is capable of metabolizing expanded polystyrene (EPS), a durable single-use plastic, when in its larval stage, mealworms. EPS consumption studies were conducted on mealworm, beetle, and co-culture habitats with a one-week acclimation period and a three-week experimentation period to compare the EPS consumption rate at each stage. Subsequent experiments tested various beddings (oats, beads), supplemental nutrients (spinach, protein powder paste, cucumbers, lemon slices), and EPS pre-treatments (lemon-lime soda, lemon juice, tomato paste) to determine the effect of those variations on mealworm EPS consumption. It was concluded that one mealworm consumes EPS at least fifty times faster than one beetle. EPS biodegradation rates were estimated under the assumption that 48.2% of consumed EPS was biodegraded by mealworm gut bacteria into carbon dioxide and biomass. It was found that EPS biodegradation rates increased 34.8% in habitats with inedible bead beddings compared to those with an edible oat bedding. EPS biodegradation rates by mealworms were also seen to increase 482% in habitats where the EPS was pre-treated with lemon-lime soda and 125% in habitats with a spinach supplemental nutrient compared to EPS biodegradation rates in a habitat with no supplemental nutrient or pre-treatment. Each supplemental nutrient and EPS pre-treatment variation in an individual inedible bead bedding improved the mealworm consumption rate of EPS. It was determined that approximately four mealworms could degrade EPS at least as quickly as natural biodegradation. These findings suggest that habitat conditions strongly affect EPS consumption rates by mealworms. • Mealworm consumption rates of EPS are fifty times greater than those of beetles. • Mealworm EPS consumption rates are lower in edible beddings than inedible beddings. • EPS consumption rates by T. molitor improved with cups pre-treated in acidic media.