The behavior and biochemical adaptations of 3 generalist insect species (Tettigonia viridissima L., Ruspolia nitidula Scopoli, and Conocephalus discolor Thunberg) and 3 specialists (Galeruca tanaceti L., Chrysolina geminata Payrtull, and Cloantha perspicillaris Boisduval) to the hypericin-containing leaves of Hypericum perforatum were investigated in southwestern France. The generalists preferentially fed on the part of the leaf lacking the phototoxic, hypericin-laden dark glands. The specialists showed no discriminatory feeding pattern but exhibited a negative phototaxis that is presumed to be an efficient strategy to circumvent the light-induced toxicity of hypericin. The constitutive and hypericin-inducible activities of glutathione reductase and glutathione S-transferase, 2 antioxidant enzymes which are considered to be biochemical adaptations used by phytophagous insects to attenuate the oxidative stress caused by photosensitization, were determined in the fatbody and midgut of T. viridissima, C. discolor, G. tanaceti, and G. geminata. The specialist insects had lower constitutive activities of glutathione S-transferase and glutathione reductase than the generalists, although the application of hypericin induced the activity of glutathione S-transferase in specialist insects only. Insects with different lifestyles therefore are capable of circumventing the phototoxic effects of hypericin by appropriate behavioral and biochemical strategies.
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