Pyrethrum-extract induced autophagy in insect cells: A new target?

Pyrethrum extract (PY) is a natural insecticide that is extensively used across the world, and its insecticidal activity is attributed to the presence of six active esters known as pyrethrins. PY targets the nervous systems of insects by delaying the closure of voltage-gated sodium ion channels in the nerve cells. However, limited information is available regarding the toxicity and detailed mechanisms of PY activity. This study is aimed at understanding the toxicity effect and the underlying mechanisms of PY in cellular level, which have not yet been investigated on the non-nervous system of insects. Results of the MTT assay showed that the viability of Sf9 cells was inhibited by PY in a time- and concentration-dependent manner, and observation under a microscope revealed accumulation of intracellular vacuoles. Monodansylcadaverine staining analysis and transmission electron microscope images revealed typical autophagic morphological changes in PY-treated Sf9 cells. Autophagy-related proteins such as LC3, p62, and beclin-1 were detected using by Western blotting. Protein expression levels of LC3-II and beclin-1 were upregulated while that of p62 was markedly downregulated in a dose-dependent manner upon the PY treatment in Sf9 cells. In conclusion, these results indicate that PY could induce autophagy in the non-nervous system of insects which may contribute to its insecticidal mechanism.