title: Efficacy of insecticide mixtures against pyrethroid- and organophosphate-resistant populations of Spodoptera litura (Lepidoptera: Noctuidae).
abstract: BACKGROUND
  Spodoptera litura (F.) is an important pest worldwide, with over 112 host plants, and is exposed to insecticides throughout the year, resulting in the rapid development of resistance. Insecticide mixtures can delay the development of resistance more effectively than sequences or rotations. Cypermethrin, deltamethrin, profenofos, chlorpyrifos and fipronil were assessed separately and in mixtures against laboratory susceptible S. litura and two field-collected populations.
  
  
  RESULTS
  The field-collected population from Khanewal (KWL) was significantly more resistant to cypermethrin, deltamethrin, chlorpyrifos and profenofos than one collected from Muzaffar Garh (MGH). Mixtures of cypermethrin + chlorpyrifos or profenofos and of deltamethrin + chlorpyrifos or profenofos at 1:1, 1:10 and 1:20 ratios significantly increased (P < 0.01) toxicity to cypermethrin and deltamethrin in field populations. The combination indices of cypermethrin + chlorpyrifos at 1:1 and 1:10 ratios and cypermethrin + fipronil at 1:1, 1:10 and 1:20 ratios for the KWL strain and of cypermethrin + profenofos or fipronil at 1:1, 1:10 and 1:20 ratios for MGH were significantly below 1, suggesting synergistic interactions. The inhibitors DEF and PBO largely overcame resistance to deltamethrin, cypermethrin and profenofos, suggesting that resistance to the insecticides was associated with esterase and monooxygenase detoxification respectively.
  
  
  CONCLUSIONS
  Chlorpyrifos, profenofos and fipronil could be used in mixtures to restore cypermethrin and deltamethrin susceptibility. These findings may have considerable practical implications for S. litura resistance management.
authors.affiliation: Department of Entomology, University College of Agriculture, Bahauddin Zakariya University, Multan 60800, Pakistan.
authors.forename: Munir
authors.initials: M
authors.lastname: Ahmad
authors.forename: Mushtaq Ahmed
authors.initials: MA
authors.lastname: Saleem
authors.forename: Ali H
authors.initials: AH
authors.lastname: Sayyed
mesh_terms: D000818:Animals; D004390:Chlorpyrifos / Q000494:pharmacology; D004338:Drug Combinations; D004357:Drug Synergism; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D010755:Organophosphates / Q000494:pharmacology*; D063086:Organothiophosphates / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011722:Pyrethrins / Q000494:pharmacology*; D018411:Spodoptera / Q000187:drug effects* / Q000502:physiology
chemical_list: D004338:Drug Combinations; D007306:Insecticides; D010755:Organophosphates; D063086:Organothiophosphates; D011720:Pyrazoles; D011722:Pyrethrins; C024273:profenofos; D004390:Chlorpyrifos; C082360:fipronil