Systematic effects of phytoecdysteroids on the cabbage aphid Brevicoryne brassicae (Sternorrhyncha: Aphididae)

Abstract

The systemic effects of phytoecdysteroids were investigated by applying tested compounds to the roots of the rape plants. Evaluation of the effects was based on mortality, longevity, rate of development and fecundity of the cabbage aphid (Brevicoryne brassicae L., Sternorrhyncha: Aphididae) feeding on the shoot of the treated plants. The major ecdysteroid compounds tested were natural products isolated from a medicinal plant Leuzea carthamoides DC (Willd.) Iljin (Asteraceae): 20-hydroxyecdysone (20E), ajugasterone C (ajuC) and polypodine B (polyB). The compounds were tested in two concentrations (0.07 and 0.007 mg/ml) in water. In addition, we have also investigated the systemic effects of a special Lc-Ecdy 8 fraction isolated from L. carthamoides, which contained 20E, ajuC and polyB and at least six other minor compounds in addition to the above indicated ecdysteroids. HPLC analysis of the Lc-Ecdy 8 fraction indicated the presence of makisterone A and inokosterone in minor quantities. It appeared that all ecdysteroid compounds tested, with the exception of the most common, 20E, decreased the fecundity of cabbage aphids which fed on the contaminated rape plants. The mortality of larvae and adults significantly increased on plants treated with the Lc-Ecdy 8 fraction, and with ajuC or polyB compounds containing structural substituents in rather unusual positions. The most common phytoec-dysteroid, 20E, with the typical and characteristic ecdysteroid structure, was the best tolerated of all phytoecdysteroi ds tested.