Degeneration of the midgut epithelium in Epilachna cf. nylanderi (Insecta, Coccinellidae): apoptosis, autophagy, and necrosis

Abstract

This study investigates mechanisms of adaptation to metal toxicity peculiar to the midgut epithelium of Epilachna cf. nylanderi (Mulsant, 1850) (Coccinellidae). This species of beetle has currently been identified in only one locality in South Africa and is known to feed on the nickel hyperaccumulator Berkheya coddii Roessl. (Asteraceae), an endemic plant species of the South African ultramafic ecosystem. Our focus involves an analysis of the morphological features of cells forming the midgut epithelium, which is the first organ exposed to toxic levels of metals ingested by the insect. Through the three key processes of apoptosis, necrosis, and autophagy, excess metals are eliminated from the organism and homeostatic conditions are maintained. Apoptosis and necrosis are both known to be involved in the degradation of midgut epithelial cells, while the role of autophagy is mainly implicated in the disintegration of the organelles of cells. This study reports on the participation of these three key degenerative processes in the removal of excess metals based on targeted observations of the insect midgut epithelium by light and electron microscopies. Additionally, the TUNEL reaction was specifically used to detect apoptosis.