Biochemical and Molecular Analysis of Gut Microbial Changes in Spodoptera littoralis (Lepidoptera: Noctuidae) to Counteract Cry1c Toxicity

Bacillus thuringiensis (Bt) represents one of the most economical biopesticides to date. It produces toxins with insecticidal activity against many agricultural pests, including members of the genus Spodoptera. However, Bt tolerance leads to inefficiency in biological control. To overcome this problem, discovering the hidden cause(s) for the evolution of insect tolerance against Bt is of great importance. We hypothesized that changes in the gut microbiota due to the frequent application of Bt is one of those hidden causes. To investigate this hypothesis, we studied the effect of Bt Cry1c application on the Spodoptera littoralis larval gut microbiota in both Bt-susceptible and Bt-tolerant populations. The results revealed changes in the diversity and abundance of gut bacterial composition between the susceptible and tolerant populations. A high abundance of Enterococcaceae was detected in the tolerant population. Interestingly, Cry1c tolerance eliminates the bacterial genera Klebsiella and Serratia from the larval midgut. These changes may confirm the mechanism developed by Spodoptera larvae to counteract Bt Cry1c toxicity. Understanding the B. thuringiensis–gut microbiota interaction may help in improving biocontrol strategies against agricultural pests to overcome the evolution of tolerance.