Short communication First detection of chlorfenapyr (Secure ® ) resistance in two-spotted spider mite (Acari: Tetranychidae) from nectarines in an Australian orchard G.A. HERRON* and J. ROPHAIL NSW Agriculture, EMAI, PMB 8, 2570 Camden, Australia; *Author for correspondence Accepted 24 March 2003 Key words: Chlorfenapyr, Control failure, Cross-resistance, Resistance management, Tetranychus urti- cae Abstract. Chlorfenapyr resistance (2.9- and 19.9-fold respectively at LC 50 and LC 99 level) was detected in Tetranychus urticae Koch causing control failure following a single application of product to nectar- ines. Introduction Chlorfenapyr (AC-303-630) was first synthesised and characterised by the Ameri- can Cyanamid Company in 1988 (Treacy et al. 1994). It is a pyrrole class pro-in- secticide/acaricide activated by the oxidative in vivo removal of its N-ethoxymethyl group (Treacy et al. 1994). Chlorfenapyr resistance causing control failure against two-spotted spider mite T. urticae is currently unknown although low 2.2-fold chlorfenapyr resistance at LC 50 was associated with tebufenpyrad resistance in 1997 (Herron and Rophail 1998). Chlorfenapyr was first registered for use in Australia in September 1998 in cot- ton against Helicoverpa spp. and T. urticae with registration following in horticul- ture from January 2000 against T. urticae on peaches and pears. Here we report the first chlorfenapyr control failure against T. urticae linked to resistance. We addi- tionally tested mites to previously used chemicals to detect cross-resistance. Materials and methods Mites were tested against commercially available formulations of chlorfenapyr 360 g/L Suspension Concentrate (SC) (Secure 360 SC Insecticide-miticide, BASF Aus- tralia Ltd); tebufenpyrad 200 g/kg Wettable Powder (Pyranica ® Miticide, Novartis Crop Protection Australia Pty Ltd) and; pyridaben 250 g/L SC (Sanmite ® Miticide, Crop Care Australasia Pty Ltd). © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Experimental and Applied Acarology 31: 131–134, 2003.