Use of waste polystyrene as feed for mealworms (Tenebrio molitor)

Abstract

This study aimed to determine what percentage of the feed provided to the mealworm larvae of Tenebrio molitor (MWL) could be substituted by polystyrene (PS) whilst retaining mealworm viability. The survival and growth rates, as well as the general performance of the larvae, were followed for a 6-week duration. Four test groups in three independent replicates of MWL, each with 300 larvae at the 8th instar, were fed on varying PS-bran percentages for six weeks under standard growth environment conditions. The four feeding regimes were 0, 50, 75 and 100% PS. The remainder of the feed for the 0, 50 and 75% groups was wheat bran. A 5g carrot supplement was provided for all groups weekly. The mealworms were monitored for mortality, percentage weight gain (%WG) and percentage length gain (%LG), and changes in their lipid and protein content at the end of the 6-week trial. Feeding solely PS did not provide the best degradation of PS, with only 27.39% degradation in six weeks. The 75% PS treatment had the lowest %PS consumption at 21.74%. The best alternative was to provide a feed consisting of 50-50 PS-wheat bran supplemented with carrots giving the highest %PS consumption at 31.06%. Furthermore, over six weeks, the 50% PS treatment larvae had the best %LG and %WG at 47.1% and 278.6%, respectively. By comparison, the 100% PS treatment achieved a %LG and %WG of 36.6% and 205.4 respectively. Mortalities of the 50% PS treatment were of 54.7%, similar to the 75% PS group, whilst, for the 100% PS, mortalities were 73.89%. The control group achieved the lowest mortalities at 22.78%. An additional test was conducted to investigate if a diet consisting of 50% PS significantly affected the protein and lipid content of the MWL compared to the control group. Analysis showed a statistically significant difference in protein content, with the 50% PS diet resulting in a higher protein content of 56.49% and 25.51 % lipid content, on a dry matter basis, when compared to the control group. In conclusion, the 50% PS treatment larvae gave the best larval growth and survival rates out of the three treatments with PS provided in their diet, whilst the 100% PS gave poor results as PS degradation was not as efficient in this test group. A better approach to making use of waste PS is actually to provide the PS as part of a diet supplemented with natural feeds, such as wheat bran and carrots. For the commercialising of this concept, further studies need to be conducted.