Insecticidal activity of a native Australian tobacco, Nicotiana megalosiphon Van Heurck & Muell. Arg. (Solanales: Solanaceae) against key insect pests of brassicas

Concerns over the harmful effects of synthetic insecticides have stimulated interest in alternative pest management tactics including botanical insecticides that provide novel modes of action against pests that have developed resistance against synthetic insecticides. Much work has been conducted using plants native to various developing countries but the Australian flora has been little explored as a source of novel plant protection treatments. Here we report potent insecticidal properties of the Australian plant, native tobacco Nicotiana megalosiphon against three key pests of brassicas: the diamondback moth (Plutella xylostella), cabbage aphid (Brevicoryne brassicae) and the green peach aphid (Myzus persicae). Aqueous extracts (1%, 5% and 10% w/v) of N. megalosiphon gave up to 100% control of P. xylostella; better than the recommended rate of tau-fluvalinate (a synthetic pyrethroid) or equivalent extracts of a second Australian native plant, Mentha satureioides. Treatment with N. megalosiphon also gave 100% control of B. brassicae at the highest two concentrations, and of M. persicae at the highest concentration. In a second study using F1 P. xylostella survivors of tau-fluvalinate treatment, the highest two rates of N. megalosiphon caused 100% mortality though efficacy of tau-fluvalinate was eroded compared with use on the previous generation. Chemical analysis of N. megalosiphon recorded the presence of anabasine at 5.2 μg/ml in water extracts of leaves and 59.4 μg/ml in methanol extracts of leaves. While these concentrations were low particularly for the water extracts they might nevertheless explain the biological activity of N. megalosiphon.