Efficacy of aqueous extracts of black alder (Alnus glutinosa GAERTN.) and black elderberry (Sambucus nigra L.) in reducing the occurrence of Phyllotreta spp., some lepidopteran pests and diamondback moth parasitoids on white cabbage

The insecticidal and antifeedant effects of aqueous extracts from two common plants (black alder Alnus glutinosa and black elderberry Sambucus nigra) on the occurrence of flea beetles (Phyllotreta spp.), as well as lepidopteran pests like the diamondback moth Plutella xylostella, small white butterfly Pieris rapae, large white butterfly Pieris brassicae, cabbage moth Mamestra brassicae and the Plutella xylostella parasitoid complex were investigated on white cabbage in 2008-2009. Aqueous extracts of black elderberry Sambucus nigra significantly reduced numbers of flea beetles Phyllotreta spp., eggs of Pieris rapae and P. brassicae, and larvae and pupae of Plutella xylostella on the cabbage. The aqueous extract of Alnus glutinosa was less effective. Parasitoids had the greatest impact on reducing numbers of diamondback moth: the dominant species was Diadegma fenestralis. The smallest number of parasitoids was reared from pupae collected from plots where the cabbages had been sprayed with the Sambucus nigra extract.