Volume 24, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Larvae of a field strain of Coq. manifesting a broad spectrum of resistance to organophosphorus (OP) insecticides were selected further by methyl parathion pressure in the laboratory. There was a 6.9× further increase in resistance to methyl parathion in larvae, i.e., from a 13.4× level of resistance in the parental strain to 93.5× level in the F generation. With the exception of fenthion and malathion, cross resistance in larvae toward other OP insecticides increased from 1.1- to 8.7-fold over the levels of resistance in the parental strain. The F larval population exhibited high levels of cross-resistance to chlorpyrifos (29.6×), fenitrothion (49.4×), parathion (55.6×), fenthion (76.8×), and chlorpyrifos-methyl (253.8×). The high levels and broad spectrum of resistance to diverse OP compounds suggest the involvement of more than one mechanism in resistance. Larval selection also affected the spectrum of OP resistance in adults. The F adult population exhibited high levels of resistance to dichlorvos (48×) and chlorpyrifos-methyl (40.1×). Both larvae and adults of the F population manifested no resistance to the carbamate insecticides propoxur, Mobam®, Landrin® or carbaryl, or to the chrysanthemate insecticide cismethrin. Resistance to the OP insecticides methyl parathion, parathion, fenitrothion, fenthion and chlorpyrifos-methyl was found to be fairly stable over nine generations in the absence of methyl parathion selection pressure.


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