title: Acaricide toxicity and resistance in larvae of different strains of Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae).
abstract: The toxicities of eight structurally different acaricidal compounds to six-legged larvae (first motile stage) of three laboratory strains of the two-spotted spider mite, Tetranychus uritcae, and the European red mite, Panonychus ulmi, were evaluated following spray application. The larvae of five field-derived strains of T urticae originating from France, Italy, Brazil, California and Florida were also tested for their susceptibilities to discriminating concentrations of several acaricides resulting in 95% mortality when applied to the organophosphate-resistant laboratory reference strain WI. The spray bioassay used was robust and gave repeatable results with a wide range of acaricidal compounds, irrespective of their mode of action (ovo-larvicides or primarily acting on motile life stages). Compounds tested were abamectin, azocyclotin, chlorpyrifos, clofentezine, deltamethrin, fenpyroximate, hexythiazox and pyridaben. Larvae of one of the laboratory strains of T urticae, AK, originally collected in Japan in 1996 and maintained without further selection pressure, exhibited 2000- and > 4000-fold resistance to the mitochondrial electron transport inhibitors pyridaben and fenpyroximate, respectively. Another strain of T urticae, AU, obtained from Australia and maintained in the laboratory under selection with hexythiazox and clofentezine since 1987 showed > 770- and > 1000-fold resistance to clofentezine and hexythiazox, respectively. The same resistance pattern was observed against larvae of a laboratory strain of P ulmi, CE, also selected with hexythiazox. Larvae of one of the field-derived strains of T urticae, BR, showed a lower susceptibility to a number of compounds, whilst the others were susceptible to all compounds except the organophosphates.
authors.affiliation: Bayer AG, Agrochemicals Division, Research Insecticides, D-51368 Leverkusen, Germany. RALF.NAUEN.RN@bayer-ag.de
authors.forename: R
authors.initials: R
authors.lastname: Nauen
authors.forename: N
authors.initials: N
authors.lastname: Stumpf
authors.forename: A
authors.initials: A
authors.lastname: Elbert
authors.forename: C P
authors.initials: CP
authors.lastname: Zebitz
authors.forename: W
authors.initials: W
authors.lastname: Kraus
mesh_terms: D000818:Animals; D001681:Biological Assay; D004351:Drug Resistance; D004579:Electron Transport / Q000187:drug effects; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000145:classification / Q000187:drug effects*; D007928:Lethal Dose 50; D008925:Mites / Q000145:classification / Q000187:drug effects*; D008928:Mitochondria / Q000187:drug effects
chemical_list: D007306:Insecticides