Mealworm frass as a potential biofertilizer and abiotic stress tolerance-inductor in plants

Abstract Frass from the insect Tenebrio molitor can be applied as an organic fertilizer due to its nutritional content. In this study insects were fed on different types of food producing excrement with different compositions. This allowed us to compare the potential effect of the excrement on plant growth promotion and to test its ability to increase tolerance to abiotic stresses such as drought, excess water and salinity. The best results were obtained when the insects were fed a diet low in fat and starch content. Moreover, a microbiological study using the excrement produced showed that the presence of microorganisms improved plant growth parameters, in the absence or presence of stress conditions. The analysis of the microbiome through massive parallel sequencing, as well as the analysis of the capacity of several microbial isolates to promote plant growth, showed that several microorganisms present in the excrement are plant growth promoters (PGPs). Our findings indicate that the frass produced by these insects, due to its nutritional content and associated microbiota, can be potentially used as a biofertilizer in organic farming. However, this potential dramatically varies according to the insect's diet. Further analyses should be performed to set the optimal time and amount of application for the different aimed plants.