Resistance to pyrethroid insecticides in the spotted tentiform leafminer, Phyllonorycter blancardella (Lepidoptera: Gracillariidae), in southern Ontario

Population of the spotted tentiform leafminer, P. blancardella (F.), developed 4- to 6-fold resistance to permethrin and fenvalerate after ca. 4-5 years of use. These populations showed cross resistance to all other pyrethroids (4- to 17-fold) and to DDT (ca. 39-fold). Resistance was not affected by addition of synergists such as piperonyl butoxide, MGK 264, DEF, or triphenyl phosphate and, therefore, is probably due to a nonmetabolic knockdown resistance-type mechanism. Surveys indicated that resistance has become widespread across southern Ontario from the Simcoe are east to Smithfield but not in the Essex-Kent or Meaford areas. Recently, higher levels (ca. 10-fold) of resistance to permethrin (and deltamethrin) were found in samples from near Bowmanville.