Effects of allelochemicals from first (Brassicaceae) and second (Myzus persicae and Brevicoryne brassicae) trophic levels on Adalia bipunctata

Three Brassicaceae species, Brassica napus (low glucosinolate content), Bra ssica nigra (including sinigrin), and Sinapis alba (including sinalbin) wer e used as host plants for two aphid species: the generalist Myzus persicae and the specialist Brevicoryne brassicae. Each combination of aphid species and prey host plant was used to Feed the polyphagous ladybird beetle, Adal ia bipunctata. Experiments with Brassicaceae species including different am ounts and kinds of glucosinolates (GLS) showed increased ladybird larval mo rtality at higher GLS concentrations. When reared on plants with higher GLS concentrations, the specialist aphid, B. brassicae, was found to be more t oxic than M. persicae. Identification of GLS and related degradation produc ts, mainly isothiocyanates (ITC), was investigated in the first two trophic levels, plant and aphid species, by high-performance liquid chromatography and gas chromatography-mass spectrometry, respectively. While only GLS wer e detected in M. persicae on each Brassicaceae species, high amounts of ITC were identified in B. brassicae samples (allyl-ITC and benzyl-ITC from B. nigra and S. alba, respectively) from all host plants. Biological effects o f allelochemicals from plants on predators through aphid prey are discussed in relation to aphid species to emphasize the role of the crop plant in in tegrated pest management in terms of biological control efficacy.