The impact of some inorganic substances on change in body mass of Tenebrio molitor (Coleoptera, Tenebrionidae) larvae in a laboratory experiment

Addition of low concentrations of metal ions to the diet of saprophagous insects can impact on their metabolism over a short period of time, causing an increase or decrease in their body mass. This article presents a 14-day laboratory experiment evaluating the changes in the body mass of larval stage 3 of Tenebrio molitor (Linnaeus, 1758) induced by adding different inorganic substances (350 mg kg⁻¹ of dry fodder) to the diet of the larvae. Following the addition of inorganic substances to the fodder, the most marked differences compared to the control were observed in the groups which consumed substrate with lead nitrate (the mass of the larvae increased on average by 102.6% compared to increase in mass in the control variant of the experiments), cobalt nitrate (by 96.9%), calcium chloride (by 89.1%) sodium triphosphate (by 86.0%), zinc chloride (by 83.5%). A nonsignificant effect (a tendency of increase in the body mass) on T. molitor larvae was caused by manganese sulfate (by 57.8%), aluminium nitrate (by 57.3%), iron oxide (by 51.5%), barium nitrate (by 47.9%), orthophosphoric acid (by 47.4%), manganese chloride (by 46.5%), calcium carbonate (by 27.7%), iron sulfate (by 24.2%) and ammonium heptamolybdate (by –7.5%). Therefore, 5 out of the 15 studied inorganic substances significantly stimulated the increase in the body weight of T. molitor larvae, and 7 manifested these capacities at the level of tendency (stimulated an increase in body weight averaging 43–58% over the 14-day experiment). The obtained data indicate a necessity for further study on the impact of inorganic pollutants on different stages of insects.