Toxicity of Deltamethrin, Chlorpyriphos and Fenvalerate in Rhizopertha dominica Population Selected for Resistance to Certain Compounds

Population of Rhizopertha dominica Fab. selected for resistance eb single ere-storage application of deltamethrin (1 μg g−1), pirimiphos methyl (15 μg g−1) and a newer PGP-2 (code name, awaiting patent) along with the laboratory susceptible culture tested for resistance to deltamethrin, chlorpyriphos methyl and fenvalerate after two years of wheat storage indicated no appreciable resistance in various selections except for 2.6 fold resistance in deltamethrin selection and 1.8 fold resistance in pirimiphos methyl selections against deltamethrin. Similarly, pirimiphos methyl selections exhibited only 1.9 fold resistance to chlorpyriphos methyl. No cross-resistance could be observed between chlorpyriphos methyl and deltamethrin. Deltamethrin selection proved more vulnerable to fenvalerate than the susceptible culture indicating the resistance mechanism to be different in these two pyrethroids. PGP-2 observed to be very effective and safer grain protectant in our preliminary laboratory trials, strikingly, rendered the selected population more prone to deltamethrin, chlorpyriphos methyl and fenvalerate toxicity suggesting its promised role for insecticide resistance management in this insect species.