Detection of Phosphine Resistance in Field Populations of Four Key Stored-Grain Insect Pests in Pakistan.

In Pakistan, the control of stored-product insect pests mainly relies on the use of phosphine gas along with other control tactics. The aim of this study was to determine the level of phosphine resistance among ten differently located populations of the lesser grain borer, (F.) (Coleoptera: Bostrychidae), the granary weevil, (L.) (Coleoptera: Curculionidae), the red flour beetle, (Herbst) (Coleoptera: Tenebrionidae) and the khapra beetle, Everts (Coleoptera: Dermestidae). Laboratory-susceptible populations of all insect species were also considered in the experiments. Concentration-response bioassays were conducted for each species. All of the tested populations (10 out of 10) of each species were found to be resistant to phosphine, but varied in their level of resistance. Probit analysis estimated LC at 2.85, 1.90, 2.54 and 2.01 ppm for laboratory-susceptible populations of , , and , respectively. Against , the highest and lowest resistance levels were observed in the Rahim Yar Khan (LC at 360.90 ppm) and Rawalpindi (LC at 210.98 ppm) populations, respectively. These resistant populations were 126.67- and 74.02-fold more resistant than the laboratory population. The Multan and Lahore populations of exhibited the maximum (LC at 122.81 ppm) and minimum (LC at 45.96 ppm) resistance levels, respectively, i.e., they were 64.63- and 24.18-fold more resistant than the laboratory population. The Layyah population of showed the maximum resistance level (LC at 305.89 ppm) while the lowest was observed in the Lahore population (LC at 186.52 ppm), corresponding to 120.42- and 73.43-fold more resistant than the laboratory population, respectively. Regarding , the Layyah population showed the maximum resistance level (LC at 169.99 ppm) while the Lahore population showed the minimum resistance (LC at 74.50 ppm), i.e., they were 84.57- and 37.06-fold more resistant than the laboratory population, respectively. Overall, presented the highest resistance level, followed by , and . The current study suggests that the application of phosphine may not be an adequate control strategy for the management of the above tested insect pests in Pakistan.