Pyrethroid resistance and selection against Trogoderma granarium (Everts) in Punjab, Pakistan

Current study was designed to investigate the current susceptibility levels of field collected strains of T. granarium (Everts) from Punjab, Pakistan. T. granarium populations were collected from different areas of Punjab i.e., Lahore, Sheikhupura, Gujranwala, Bahawalpur, Bhakkar and Faisalabad, were evaluated for their relative resistance or susceptibility in comparison to laboratory reared strain against pyrethroids. Filter paper impregnation method was used to assess the contact toxicity of pyrethroids (technical grade deltamethrin, alpha-cypermethrin, cypermethrin and bifenthrin) against 4(th) instar larval stage of T. granarium. Mortality responses were evaluated under constant temperature and relative humidity (r.h.) at 32 +/- 2 degrees C and 65 +/- 5 r.h. respectively. Data was recorded after 24, 48 and 72 h of treatment and completely randomized design (CRD) were used with four replications. Experiments were conducted in Grain Research Training and Storage management cell, University of Agriculture, Faisalabad, Pakistan during year 2018-19. Bioassays showed that field collected strains were resistant to all test insecticides. Very low to moderate level of resistance was found in field strains. Bahawalpur strain showed highest resistance ratios of up-to 12.7, 18.9, 4.63 and 8.27 for deltamethrin, bifenthrin, alpha-cypermethrin and cypermethrin respectively, after 72 h of exposure to treatment. Bhakkar strain also showed moderate resistance following Bahawalpur strain. Lahore and Faisalabad collected strains were susceptible as compared to other field strains. In-vitro selection for deltamethrin revealed increase in resistance up-to 18.7 folds after selection for 7 generations by maintaining selection pressure at 80% mortality. Reversion in resistance occurred when strain was again reared for next 5 generations without insecticide exposure and resistance values decreased to 7.74 folds at G(12). DR value for change in resistance was -0.07. The effectiveness of commonly used pyrethroids for the management of T. granarium was significantly reduced in the field populations exhibiting low to moderate resistance. Long-term use of insecticides with similar mode of action could be the reason for the development of resistance. Multi-tactical approach with integrated pest management (IPM) framework may prolong the effectiveness of pyrethroids in the T. granarium management.

Automated summary

The study investigated the susceptibility levels of field collected strains of T. granarium to pyrethroids in Punjab, Pakistan. Results showed varying levels of resistance among different strains, suggesting long-term use of insecticides with similar mechanisms might contribute to resistance development.