ORGANOPHOSPHATE RESISTANCE IN SPIDER-MITES (ACARI, TETRANYCHIDAE) FROM COTTON IN AUSTRALIA

Tetranychus urticae Koch was resistant to all organophosphates (OPs) t ested. The demeton-S-methyl resistance was extremely high (maximum res istance factor (RF) 650X), as was the dimethoate resistance (maximum R F 750X). The parathion resistance was high (maximum RF 78X), while the profenofos resistance in T. urticae remained stable from 1976 until 1 988 (approximately 15X) and that of monocrotophos from 1976 until 1989 (approximately 40X) after which the resistance rose. The resistance i n T. urticae peaked in the 1995 season at levels of >100X for profenof os and >400X for monocrotophos, rendering both chemicals ineffective. Tetranychus ludeni Zacher was also resistant to all the OP chemicals t ested, but at lower levels than for T. urticae. The LC50 values indica ted that the demeton-S-methyl and monocrotophos resistance in T. luden i was an order of magnitude less than for T. urticae. The maximum prof enofos resistance levels against T. ludeni (6.5X) were approximately o ne-quarter those of the values and maximum profenofos resistance level s against T. urticae (30X). The parathion LC50 dimethoate RFs indicate T. ludeni to be ultimately only half as resistant as T. urticae. We c onsider that the relative lack of tolerance to OPs exhibited by T. lud eni may have contributed to its apparent disappearance from Australian cotton. Tetranychus urticae was the dominant mite pest in Australian cotton during 1976-1995. Tetranychus ludeni reached damaging levels in the late 1970s but virtually disappeared from cotton during the 1980s . (C) 1998 Chapman & Hall Ltd.