Effects of light on fecal case-bearing larvae of the leaf beetle
image: Leaf beetles construct faecal cases to protect against light exposure and damage.
Credit: Osaka Metropolitan University
In plants, light energy absorbed by chlorophyll (Chl) in photosystems is converted into chemical energy required for carbon assimilation. However, Chl released from the photosynthetic and photoprotective machinery can transfer excitation energy to oxygen, producing reactive oxygen species (ROS) and causing oxidative damage. While the phototoxic effects of Chl and its catabolites are well studied in plants, they remain largely unexplored in herbivores.
To examine the relationship between herbivory and protection against Chl phototoxicity, Osaka Metropolitan University researchers investigated larvae of the leaf beetle Chlamisus laticollis, which feed on Rhododendron leaves and construct a faecal case. When the faecal case was removed from C. laticollis larvae, strong light exposure reduced larval survival and growth. Although the effect was independent of light wavelength (red 655 nm, green 530 nm, blue 470 nm), some case-removed larvae lost weight under blue light, suggesting a partial negative effect of blue light on their growth. Leaf Chls ingested by larvae appeared to be rapidly dissociated from photosystems but possibly associated with some components that limit photoexcitation. Although ingested Chls were gradually degraded to phototoxic catabolites in larvae, lipid peroxide levels, indicating ROS production, were unaffected by the presence of the case, the amount of Chl catabolites, or blue light exposure.
These results suggest that although C. laticollis larvae are shielded from sunlight by their faecal case, they retain intrinsic mechanisms that attenuate Chl phototoxicity. Chl catabolites were also detected in the faecal case, suggesting a possible role for these pigments in ecological interactions.
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