Efficacy of plant metabolites of imidacloprid against Myzus persicae and Aphis gossypii (Homoptera: Aphididae)

The metabolism of the chloronicotinyl insecticide imidacloprid is strongly influenced by the method of application. Whilst in foliar application most of the residues on the leaf surface display unchanged parent compound, most of the imidacloprid administered to plants by soil application or seed treatment is metabolized more or less completely, depending on plant species and time. The present study revealed that certain metabolites of imidacloprid which have been described in crop plants are highly active against aphid pests in different types of bioassays. Some of these metabolites showed a high oral activity against the green peach aphid (Myzus persicae), and the cotton aphid (Aphis gossypii). The aphicidal potency of the metabolites investigated was weaker in aphid dip tests than in oral ingestion bioassays using artificial double membranes. The most active plant metabolite was the imidazoline derivative of imidacloprid. The LC50 values of this metabolite for M. persicae and A. gossypii in oral ingestion bioassays were in the lower ppb-range, i.e. 0.0044 and 0.0068 mg litre(-1), respectively. Most of the other reported metabolites showed much weaker activity. Compared to imidacloprid, the imidazoline derivative showed superior affinity to housefly (Musca domestica) head nicotinic acetylcholine receptors, while all other metabolites were less specific than imidacloprid. It seems possible that, after seed treatment or soil application, a few of the biologically active metabolites arising are acting in concert with remaining levels of the parent compound imidacloprid, thus providing good control and long-lasting residual activity against plant-sucking pests in certain crops. (C) 1998 SCI.