Effects of destruxin a on hemocytes of the domestic silkworm, bombyx mori

Authors: YING, FEI - Guangdong Academy Of Agricultural Sciences; HU, LINA - Guangdong Academy Of Agricultural Sciences; LI, ZHENYU - Guangdong Academy Of Agricultural Sciences; Yang, Xiangbing; Kendra, Paul; HU, QIONGBO - Guangdong Academy Of Agricultural Sciences

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2023
Publication Date: 6/2/2023
Citation: Ying, F., Hu, L., Li, Z., Yang, X., Kendra, P.E., Hu, Q. 2023. Effects of destruxin a on hemocytes of the domestic silkworm, bombyx mori. Frontiers in Microbiology. 14 : Article 1210647. https://doi.org/10.3389/fmicb.2023.1210647.
DOI: https://doi.org/10.3389/fmicb.2023.1210647

Interpretive Summary: Biological control using the entomopathogenic fungus Metarhizium anisopliae has shown potential for management of various insect pests, including tephritid fruit flies. Destruxin A (DA) is a mycotoxin isolated from M. anisopliae, but the mechanism of toxicity against insects remains unknown. To better understand the mode of action of DA, scientists from Guangdong Academy of Agricultural Science (China) and USDA-ARS in Miami, Florida used histopathological methods to investigate the effect of DA on target cells and tissues of the silkworm Bombyx mori. At low doses (i.e., 0.01µg/g), the hemocytes (phagocytic blood cells that comprise the primary immune system in insects) were the most sensitive to DA with morphological changes apparent 6 h after treatment; but the muscle cells, fat body (responsible for metabolism), and Malpighian tubules (the excretory organs) remained unaltered. At higher doses (i.e., > 0.1µg/g), the muscle cells, fat body, and Malpighian tubules showed morphological changes 24 h after treatment. This study elucidated the target sites in B. mori that responded to DA treatment, indicating that the defensive hemocytes were the first cells damaged, but higher doses could further impact other physiological processes, including muscle function, metabolism, and excretion. The results of this study will help develop mycopesticides and novel immunosuppressants for improved management of insect pests.

Technical Abstract: Destruxin A (DA) is a mycotoxin isolated from the entomopathogenic fungus Metarhizium anisopliae which has demonstrated inhibitory activity against various insect species. However, the mechanism of inhibition on target sites in insects remains unknown. In this research, the dose-response relationship between DA and morphological changes in body tissues and organs of domestic silkworm, Bombyx mori, were investigated by histopathological methods to identify the target sites that responded to DA. The results showed that responses of individual tissues and organs varied with DA dosage and treatment time. At low doses (i.e., 0.01µg/g), the hemocytes were the most sensitive to DA with morphological changes apparent at 6 h after treatment. However, the muscle cells, fat body, and Malpighian tubules were unaltered. At higher doses (i.e., > 0.1µg/g), morphological changes were observed in muscle cells, fat body, and Malpighian tubules at 24 h after treatment. The results indicated that DA can be an immunosuppressant by damaging host cells like hemocytes, and at higher doses may potentially impact other physiological processes, including muscle function, metabolism, and excretion. The information presented in the current study will facilitate development of mycopesticides and novel immunosuppressants.