The botanical eurycomanone is a potent growth regulator of the diamondback moth

Eurycomanone is a quassinoid compound that is derived from Eurycoma longifolia, and it is often used as an indicator to evaluate the active ingredients of Eurycoma longifolia. However, Eurycomanone has rarely been reported to have biological activity toward pests. In this study, we evaluated the antifeedant activity of eurycomanone against the diamondback moth(Plutella xylostella), with a non-selective AFC₅₀(the concentration that corresponds to 50% antifeedant action) value and selective AFC₅₀ of 17.5 mg/L and 14.2 mg/L, respectively, which were 2.1-fold (36.9 mg/L) and 2-fold (28.5 mg/L) lower than that of azadirachtin, respectively. In addition, eurycomanone was used to treat the roots of Brassica chinensis L. at a concentration of 100 µg/g for 72 h. The antifeedant index was found to reach 93% by tracking the leaves. After feeding with 20 µg/g eurycomanone, no pupae or eclosion were observed. To explore this mechanism, we used scanning electron microscopy to discover that eurycomanone could prevent the development of taste receptors on the maxillary palp of diamondback moth larvae. Additional electrophysiological measurements showed that eurycomanone exhibited excitatory action to the central taste neurons of diamondback moth and significantly inhibited the GABA_A receptor current. Eurycomanone exhibited significant activity as an antifeedant, inhibited growth and excelled at systemic absorption.