Effects of Toxic and Deterrent Terpenoids on Digestive Protease and Detoxication Enzyme Activities of Colorado Potato Beetle Larvae

Larvae of Colorado potato beetle, Leptinotarsa decemlineata, were fed on potato leaf disks treated with the toxic limonoids azadirone and a mixture of 1,7-di-O-acetylhavanensin and 3,7-di-Oacetylhavanensin (F18) from Trichilia havanensis (Meliaceae) and a deterrent neo-clerodane (scutalpin-B) from Scutellaria alpina (Labiatae). Azadirone, a toxicant with low mortality action, decreased esterase activity and increased glutathione S-transferase activity during the treatment period, but these detoxication enzymes reached normal levels of activity when the larvae were shifted to untreated leaf disks during the post-treatment period. The mixture of limonoids F18, a strong toxicant that produces high levels of larval mortality, significantly reduced digestive protease and esterase activities and increased glutathione S-transferase and polysubstrate monooxygenases during the treatment period. All enzymatic activities but glutathione Stransferase remained altered during the post-treatment period. Scutalpin-B, with a deterrent mode of action, did not have any significant effect on any of the enzymatic processes. We concluded that the effects of these compounds on digestive proteases and detoxication enzymes in the larval midgut of L. decemlineata larvae reflect their postulated mode of action.