Effect of Probiotics on Tenebrio molitor Larval Development and Resistance against the Fungal Pathogen Metarhizium brunneum

Abstract

In recent years, the yellow mealworm (Tenebrio molitor L.) has demonstrated its potential as a mass-produced edible insect for food and feed. However, challenges brought on by pathogens in intensive production systems are unavoidable and require the development of new solutions. One potential solution is the supplementation of probiotics in the insect's diet to obtain the double benefits of improved growth and enhanced immune response. The aim of this study was to evaluate the effects of diet-based probiotic supplementation on T. molitor larval survival, growth, and resistance against a fungal pathogen. Three probiotic strains, namely Pediococcus pentosacceus KVL-B19-01 isolated from T. molitor and two commercialized strains for traditional livestock, Enterococcus faecium 669 and Bacillus subtilis 597, were tested. Additionally, when larvae were 9 weeks old, a pathogen challenge experiment was conducted with the fungus Metarhizium brunneum. Results showed that both P. pentosaceus and E. faecium improved larval growth and larval survival following fungal exposure compared to the non-supplemented control diet. Since B. subtilis did not improve larval performance in terms of either development or protection against M. brunneum, this study suggests the need for further research and evaluation of probiotic strains and their modes of action when considered as a supplement in T. molitor's diet.

Keywords: disease; immune response; mealworm; probiotics; production.

Figure 1

Average body weight (g) of individual Tenebrio molitor larvae in the four probiotic treatment groups during the experimental period of 15 weeks. Horizontal reference line at Y = 0.12 g indicates the threshold weight of the larvae to harvest. Blue: control (C); red: Bacillus subtilis (B); green: Enterococcus faecium (E); and violet: Pediococcus pentosacceus (P). Each treatment group consisted of 10 subgroups, each with 100 larvae. Larvae were harvested at three time points: P larvae at week 9, E larvae at week 13, and C larvae at week 15, as indicated by final data points. The bars in each curve represent the standard error (±SE) from the mean weight. Significant differences (p < 0.0001) in larval weight at weeks 9, 13, and 15 are indicated by ***.

Figure 2

Kaplan–Meier curve showing the proportion of alive Tenebrio molitor larvae recorded over two weeks in four probiotic treatment groups. Blue: control (C); red: Bacillus subtilis (B); green: Enterococcus faecium (E); and violet: Pediococcus pentosacceus (P). Larvae were exposed to the fungus Metarhizium brunneum strain KVL 12–37 and observed for 14 days as a part of the fungal pathogen challenge experiment. Highest mortality was observed for fungus-treated larvae fed with B. subtilis bacterium, which was significantly different from the two probiotic treatment groups but not from the control group. The least mortality was observed for larvae supplemented with P. pentosacceus strains, which was significantly different from B. subtilis treatment groups but not from E. faecium and control groups. Different letters at the right end of the curves indicate significant differences (p < 0.05, Bonferroni adjustment for multiple comparisons) between the corresponding treatment groups.