Alterations in the expression of certain midgut genes of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) larvae and midgut histopathology in response to Bacillus thuringiensis Cry1C toxin

Abstract

Background Bacillus thuringiensis (Bt) utilization as a biological control agent is highly recommended due to its safety, specificity, and efficiency. Importance of the entomocidal Cry proteins secreted by Bt is dramatically increased subsequent Cry genes transformation into a number of economic crops, rendering them protection against insect attack. In the last decade, insect resistance against transgenic Bt crops is gradually raised in several lepidopteran pests. A better understanding of the processing of Bt Cry1C toxin in the larval midgut of the lepidopteran pest species, the cotton leaf worm, Spodoptera littoralis (Boisd.), is very important to characterize the main regulatory elements of Bt tolerance. Results The present study aimed to define factors that are involved in insect tolerance toward Bt Cry1C through evaluating the mRNA level of trypsin (Try), aminopeptidase N (APN), alkaline phosphatase (ALP), cadherin (Cad), and cytochrome P450 (CYP) in both susceptible and cry1C tolerant strains of S. littoralis. Total RNAs were extracted from susceptible and tolerant strains to construct cDNAs. Quantitative real-time polymerase chain reaction (qPCR) showed a significant upregulation of CYP gene in tolerant strain. In contrast, the levels of expression of Try, ALP, and Cad were significantly downregulated in tolerant strain. APN relative mRNA expression did not show significant differences between susceptible and tolerant strains. Histologically, the midgut of late third-instar larvae of tolerant population S. littoralis showed vacuolization of the epithelium and disruption of both the peritrophic membrane and the striated boarder compared to the susceptible strain. Conclusions Obtained data indicated a relationship between exposing to Bt Cry1C toxin and alteration of CYP, Try, ALP, and Cad expression in midgut of S. littoralis. These results may be an evidence for the important roles of CYP, Try, ALP, and Cad in the resistance development and toxicity to Bt Cry1C. The results are useful for further illustrating of Bt Cry1C processing and S. littoralis tolerance.

Baseline susceptibility of cabbage butterfly, Pieris brassicae (Linnaeus) (Lepidoptera: Pieridae) to Bacillus thuringiensis (Berliner) Cry toxins in Meghalaya

“…It was also noticed that there was not much variability shown pertaining to Cry1C toxin. These findings were in accordance with the toxicity tests conducted using the Bt Cry1C toxin against P. xylostella (Zhao et al 2001), C. suppressalis (Tang et al 2018) and S. littoralis (Khalil et al 2021) resulted in a relatively high ppm showing its evolving resistance toward the Cry toxin. P. brassicae was more sensitive to Cry1C toxin at a very low concentration and resulted in various changes in the biological parameters of the pest which are in agreement with the earlier work done by Ningthoujam et al (2017a) on H. armigera which resulted in some changes in both adult and pupal emergence.…”

Spatial and temporal distribution and bioinsecticides control of olive leaf moth in an olive orchard in Southwest of Paraná, Brazil

“…Thus, considering the great nutritional demand in the early stages, it may have caused the insect death (BEZZAR-BENDJAZIA et al, 2017). In turn, the causes of larvae mortality attributed to the Bt act are the effect on the columnar cells of the insect's mid gut, as occurs for other Lepidoptera and can be extended to P. forficifera, under the action of endotoxins contained in the protein crystal of the bacterium Bt (KHALIL et al, 2021;NASCIMENTO et al, 2022).…”