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Biodegradation of petroleum-derived plastics in mealworms has been identified with different plastic products. To date, however, the responses of mealworm larvae to plastic biodegradation have received comparatively little attention. Herein, we tested the physiological responses of mealworm larvae after biodegradation of polyethylene (PE) microplastics and evaluated the impact of supplementing co-diet bran on the PE biodegradation and mealworm homeostasis. Significant weight loss, biomass reduction, and decreased survival rates were found for the PE-fed larvae after the six-week test. The efficient removal of PE, molecular weight reduction of residual polymers, and thermal decomposition signals demonstrated the depolymerization and biodegradation. Supplementing bran significantly enhanced the biomass levels and the survival of larvae but disturbed the PE removal in the intestinal tracts. The frass (excrement) from the larvae fed with PE and PE + bran feedstocks both contained undigested residual microplastics of different sizes with no accumulation of nanoplastics. Additionally, higher levels of reactive oxygen species, antioxidant enzyme activities, and lipid peroxidation were detected for larvae fed with pure PE, whereas the oxidative stress levels could be mitigated by supplementing co-diet bran. These results provide methodological insights into assessing the physiological responses of invertebrates after plastic ingestion or under micro(nano)plastic exposure. [Display omitted] • The physiological function and growth of mealworms were negatively influenced by PE degradation. • Oxidative stress and damage were induced in mealworms after PE degradation. • Supplementation of co-diet bran can improve the physiological performance of mealworms. • The levels of oxidative stress and damage in mealworms could be mitigated by supplementing bran. • Nanoplastics could not be accumulated in the frass of mealworms after PE degradation. [ABSTRACT FROM AUTHOR]

In this study, biodegradation of polystyrene (PS) and low-density polyethylene (LDPE) by Zophobas atratus larvae was characterized to investigate fragmentation of ingested polymers, larval physiology, gut microbiota, and microbial functional enzymes over a 28-day test. The larvae maintained high survival rates and low cannibal rates, but their body fat content decreased when fed with PS or LDPE with respective consumption rates of 43.3 ± 1.5 and 52.9 ± 3.1 mg plastics/100 larvae per day. The larvae biodegraded PS via broad depolymerization and LDPE via limited-extent depolymerization. The ingested PS and LDPE were fragmented into microplastics with a mean size of 174 and 185 μm on a volume basis, and the particles with a size of 6.3 and 5.9 μm reached a maximum number, respectively, with no nanoplastics generated. Chemical modifications of the polymers were confirmed. Significant shifts and clustering in the gut microbiota were detected with the relative abundance of Citrobacter sp. increasing when PS and LDPE were fed, as reported for other species of Tenebrionidae. Microbial functional enzymes, possibly associated with plastic degradation, including arylesterase and serine-hydrolase, were upregulated in both PS-fed and PE-fed larvae. This work provides new insights into insect-mediated biodegradation of persistent plastics for future investigations. [Display omitted] • Zophobas atratus biodegraded PS and LDPE in different depolymerization patterns. • Digestive fragmentation into microplastics occurred with no nanoplastics generated. • Significant clustering in the gut microbiota was attributed to PS and LDPE digestion. • Expression levels of functional enzymes were upregulated during plastic degradation. [ABSTRACT FROM AUTHOR]