World population growth requires the development of a sustainable agriculture that allows feeding all the inhabitants of the planet, while reducing the use of agrochemicals. Currently, the insect farming industry for food and feed production is developing exponentially throughout the world; also producing insect frass with a potential utilization within agriculture and greenhouse industry. In the case of the yellow mealworm (Tenebrio molitor), few studies have been developed so far on the use of frass as a fertilizer, and there are none on its ability to activate plant defenses. By applying 2% sterilized mealworm frass to tomato we found a significant increase in its growth, demonstrating that the microbiota might not play a key role in its fertilizing capacity. In addition, the application of frass to sunflowers under different situations of nutritional deficit allowed us to determine what specific nutrients this fertilizer may be providing to the plant, finding a possible deficiency in the supply of N, but with sufficient amounts of P, K, Ca, and S. With respect to the induction of defenses, mealworm insect frass did not induce local root defenses in a root callose deposition assay in Arabidopsis thaliana under our experimental conditions. However, it activated systemic defenses in Arabidopsis thaliana by inducing defense genes in the absence of pathogen, further enhanced by infection with the necrotrophic fungus Botrytis cinerea. Therefore, mealworm frass could be a good fertilizer resource and plant defense inducer to support development of sustainable agriculture.
