Deltamethrin resistance in some diamondback moth, Plutella xylostella populations in Iran

The diamondback moth, Plutella xylostella has been developed resistance to many groups of pesticides including of pyrethroids. The present study was conducted to evaluate the toxicity of deltamethrin on the third instar larvae of six populations of the pest using leaf dipping method. The results showed that different populations had different susceptibilities to deltamethrin. At the LC50 level, the resistance ratios of the Urmia, Flaverjan, Karaj, Tehran and Naqadeh populations to deltamethrin were 20.75, 21.84, 2.00, 3.08 and 26.26-fold.  Resistant populations were selected for 15 generations and their susceptibility to deltamethrin was evaluated. Resistance levels were noticeably increased in these strains and equaled with 91.87, 82.84 and 70.42-fold in Naqadeh, Urmia and Flaverjan populations, respectively. Although, DEM and TPP had no synergistic effect on deltamethrin, treatment with PBO significantly decreased the toxicity of deltamethrin in the tested resistant strains. DEF also exhibited a moderate synergism with deltamethrin. Enzyme analysis proved that the activity of monooxygenase and esterase enzymes in the resistant strains were much stronger than that of glutathione S-transferase. The results showed that the high resistant strain (Naqadeh) of P. xylostella selected by deltamethrin exhibited high cross resistance to hexaflumuron and indoxacarb. This strain also had moderate positive cross resistance to flubendiamide and thiodicarb.