Mechanisms of insecticide resistance in the aphid Nasonovia ribisnigri (Mosley) (Homoptera : Aphididae) from France

Nasonovia ribisnigri, a main pest of salad crops, has developed resistance to Various insecticides in southern France, including the carbamate pirimic arb and the cyclodiene endosulfan, two insecticides widely used to control this aphid. Here we have investigated the mechanisms of resistance to these two insecticides by studying cross-resistance, synergism, activity of deto xifying enzymes, and possible modifications of the target proteins. Resista nce to pirimicarb was shown to be mainly due to a decreased sensitivity of the target acetylcholinesterase; this modification confered also, resistanc e to propoxur but not to methomyl and the two tested organophosphates (acep hate and paraoxon). Endosulfan resistance was associated with a moderate le vel of resistance to dieldrin, and resistance to both insecticides was due, in part, to increased detoxification by glutathione S-transferases (GST). The endosulfan resistant strain displayed the same amino acid at position 3 02 of the Rdl gene (GABA receptor) as susceptible aphids (e.g. Ala), indica ting that the Ala to Ser (or to Gly) mutation observed among dieldrin resis tant strains of other insect species was not present. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.