Petuniolides, Natural Insecticides fromPetunia parodii, Are Antagonists of GABAaReceptors

Abstract

Petuniolide C, an ergostane-type steroidal insecticide isolated fromPetunia parodii,caused immediate uncoordinated activity and salivation in fourth instar nymphs of the desert locust,Schistocerca gregaria,when injected into the hemocoel at doses as low as 0.5 μg insect−1. The LD50for petuniolide C via injection in locust nymphs (14.1 μg insect−1) is nearly identical to that for the convulsant, picrotoxinin (14.0 μg insect−1), a known inhibitor of the GABA (γ-aminobutyric acid)-mediated chloride ionophore. Petuniolide C and picrotoxinin in combination had an additive effect on locust mortality. Following topical administration, petuniolide C caused knockdown and mortality in a cyclodiene-susceptible strain of the German cockroach,Blatella germanica,but significantly reduced effects in a cyclodiene-resistant strain. Using anin vitrorat brain synaptic membrane preparation, both petuniolide C and a natural analog, petuniolide D, were shown to be weak ligands of the GABAareceptor.