The present study reports the biodegradation of polystyrene (PS) by mealworm (Tenebrio molitor) following different feeding regimes. Changes in lipids and protein were studied to evaluate possible differences in the growth and metabolic pathways of the insects depending on the diets. Thermo-gravimetric analysis of the excretions (frass) revealed a decrease in the molecular mass of the PS polymers. The insects' biomass contained less protein when PS was part of the diet, suggesting that the insects undergo a certain level of stress compared to control diets. The frass also contained lower amount of nitrogen content compared to that from insects fed a control diet. NH4+ and other cations involved in biochemical processes were also measured in insects' frass, including potassium, sodium, magnesium, and calcium, combined with a small pH change. The decrease in the mineral content of the frass was attributed to increased cellular activity in PS-fed insects. A higher amount of ceramides and cardiolipins, biomarkers of apoptosis, were also found in association with PS consumption. It was concluded that the insects could metabolize PS, but this caused an increase in its stress levels.

Optimising the production of insects for food and feed and ensuring their health are growing concerns for producers. Insects suffer from a range of insect pathogenic microorganisms, and the management of such diseases is essential. One solution is the introduction of beneficial probiotic bacteria into the diet of the insects. Here, we show that a lactic acid bacterial strain, Pediococcus pentosaceus, isolated from the gut of the mealworm, Tenebrio molitor, was able to inhibit the growth of selected insect pathogens in vitro. Using in vivo assessments of the host's fitness benefits conferred by the lactic bacterium we show a significant effect of P. pentosaceus on larval growth rate and survival into adulthood. Gut microbiota analysis focusing on bacterial composition based on 16S rRNA gene amplicon sequencing suggests that P. pentosaceus could have successfully colonised the guts, or altered their bacteria, of the larvae that received it. Finally, we discuss our results in the context of mass insect production systems and outline the remaining work needed to explore and secure the role of beneficial bacterial additives in the field.

The present study investigated the biodegradation of polystyrene (PS) plastic by mealworm (Tenebrio molitor) on different diets followed by untargeted screening of larvae gut intestine tissue and frass (manure and feed residuals) to investigate the existence of polymer-generated organic residues. Three different diets, consisting of PS, rolled barley and water were tested. PS degradation rates ranged from 16% to 23% within 15 days, with no statistical differences in survival rates. The larvae fed with ad libitum barley:PS (20:1 w/w) and water had the highest growth rate, while higher PS consumption was observed for barley:PS of 4:1 w/w. A GC-TOF-MS analysis revealed no contaminating substances in the gut intestine tissue, nor styrene or PS oligomers, whilst several bioactive compounds and traces of alkanes, mostly with small carbon chains, were present. Metabolomics analysis on the collected frass, either on the lipophilic (CHCl3) or the polar fraction (MeOH-H2O) was performed. Styrene and PS oligomers (dimers, trimers) were identified, though in a relatively low total amount, up to a total of 346.0 ng/mg 2,4 di-tert butylphenol was identified in both frass and tissue, coming from the PS polymer (Non-intentionally added substances; NIAS). Finally, in the polar fraction of frass, bioactive molecules (fatty acids, amides) were identified, together with several hydrocarbons, mostly with longer carbon chains. The formation of these substances indicated enzymatic and biochemical activity in the larvae-gut intestine. It was shown that degrading and contaminating organic compounds occur at low levels, in both gut intestine and frass, during biodegradation of PS.

The impact of adult density, reproduction period (days in the same container) and age on reproduction ofTenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) were studied. Data were analysed as total number of larvae in each container (38 cm2) and as daily reproduction per capita. The study was divided in two experiments. Experiment 1 examined the influence of four densities (0.11, 0.21, 0.42 and 0.84 beetles/cm2) and five reproduction periods (1, 2, 3, 4 and 6 days) on reproduction. Experiment 2 examined the effect of age (30-92 days) and three densities (0.11, 0.21 and 0.32 beetles/cm2) on reproduction. The total number of larvae per container was significantly affected by reproduction period and adult density, attaining the highest output at the longest reproduction period of 6 days (214±101 larvae) and highest density of 0.84 beetles/cm2 (215±112 larvae). Daily per capita reproduction, however, was highest at the second lowest density of 0.21 beetles/cm2 (8.58±3.82 larvae/female/day) and shortest reproduction period of 1 day (8.34±4.68 larvae/female/day). In experiment 2, age had a significant effect on reproduction both as total number of larvae per container and number of larvae per female per day. The highest reproduction was found when beetles were 30 days old, but reproduction was in general highest for 13-29 days old females (experiment 1). For production context the highest density of beetles provides highest output of larvae, and beetles are not expected to be stressed under these conditions.