Bemisia tabaci is an important insect pest of many crop plants and also transmits several viruses including Tomato Yellow Leaf Curl Virus (TYLCV). Intensive use of insecticides has led to the development of insecticide resistance in B. tabaci. This study was conducted to develop baseline susceptibility of B. tabaci eggs, nymphs and adults to three commonly used insecticides (deltamethrin, thiamethoxam and pyriproxyfen) on tomato, eggplant and cucurbits in Oman. Leaf-dip bioassay method was used to expose eggs, nymphs and adults of B. tabaci against insecticide treated leaves in laboratory studies. Lethal concentrations (LC10, LC50 and LC90) were calculated for the three life stages of SQU-1 (resistant-conventional) and Pairidaeza (susceptible-organic) strains. A very low level of resistance to deltamethrin was detected in adults (RF = 4.3) and nymphs (RF = 2.7). The field application rate of deltamethrin resulted in reduced mortality of 47.0-59.6% in the SQU-1 strain and 62.7-67.4% in the Pairidaeza strain. A very low level of resistance was also observed for thiamethoxam in adults (RF = 2.2) and nymphs (RF = 2.7). The determined baseline susceptibility levels of B. tabaci eggs, nymphs and adults against deltamethrin, thiamethoxam and pyriproxyfen can be used in resistance monitoring in Oman by comparing any shift from these LC50 values in future. These findings can be helpful to initiate resistance management programs to slow the resistance evolution in B. tabaci in Oman.
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