Cross Resistance Studies on Insecticide Resistant Strains of Tribolium castaneum to Some Grain Protectants

Tribolium castaneum population selected for resistance separately to carbendazim, deltamethrin, pirimiphos methyl and two new entries PGP-2 and PGP-3 (code names, awaiting patent) through their application on wheat grain singly before storage for two years and then tested for resistance to deltamethrin, chlorpyriphos and fenvalerate indicated deltamethrin resistance (x 9.17) in deltamethrin selection only. Higher resistance on the other hand was exhibited to chlorpyriphos in selections for pirimiphos methyl (x13.09), deltamethrin (x 18.64) and carbendazim (x 45.81) suggesting cross resistance in these three chemicals groups. None of the selections recorded noticeable resistance to fenvalerate except that for deltamethrin (x 3.69) indicating their resistance mechanism to be not common. Strikingly, PGP-2 and PGP-3 selections did not impart resistance to any of the tested insecticide. Instead PGP-2 rendered the T. castaneum population more susceptible by diluting resistance to the extent of 9.0 fold to deltamethrin, 2.75 fold to chlorpyriphos and 33.33 fold to fenvalerate. The significance of PGP compound in resistance management has been discussed.