PHAGODETERRENCY INDUCED BY TWO CRUCIFEROUS PLANTS IN ADULTS OF THE FLEA BEETLE PHYLLOTRETA STRIOLATA (COLEOPTERA: CHRYSOMELIDAE)

Abstract The two cruciferous plants Thlaspi arvense and Lunaria annua are largely unacceptable to the striped flea beetle, Phyllotreta striolata , which normally feeds on cruciferous plants. Results suggest that these plants contain chemical compounds that act as feeding deterrents to the beetles. Methanol fractions of the leaves of both plants deterred feeding when added to the surface of acceptable radish leaves. An alkaloid fraction of Lunaria annua was, surprisingly, not deterrent. Evidence suggests that saponins in both Lunaria annua and Thlaspi arvense may be a major reason for the low acceptability of these plants as food for Phyllotreta striolata . Commercial saponins are highly deterrent at concentrations of 0.05% and above.