Effect of selected synergists on insecticidal toxicity of deltamethrin and biochemical mechanisms on the field populations of tobacco caterpillar from Punjab, India

Abstract

Spodoptera litura (Fabricius) is an important polyphagous and destructive pest worldwide causing heavy foliage damage to more than 115 species of host plants, and is exposed to insecticides throughout the year, resulting in the rapid development of resistance. Different population’s viz., susceptible Hoshiarpur (HSP), resistant Malerkotla (MAL) and deltamethrin selected strain (MAL-Sel) of S. litura collected from different locations were treated in the laboratory by leaf dip method with deltamethrin alone and in combination with different ratios of synergists like Piperonyl butoxide (PBO), Tri phenyl phosphate (TPP) and Diethyl maleate (DEM). When PBO, TPP and DEM at ratio of 1:4 were used as synergist in the HSP, MAL and MAL-Sel strain, the synergistic ratio was 3.91, 3.66 and 3.31 for susceptible population (HSP), 8.24, 7.67 and 6.85 for resistant population (MAL), 21.30, 23.67 and 18.26 for MAL-Sel strain selected after 10 generations, respectively. The results obtained in the present study revealed that PBO at 1:4 had highest synergistic effect on the resistant population MAL (8.24 fold) whereas, PBO at 1:6 showed highest synergistic effect i.e. 4.78 folds on the susceptible (HSP) population followed by TPP and DEM (1:4). However, the stronger synergism of TPP (1:4) was 23.67 fold followed by PBO (21.30 fold) and DEM (18.26) at 1:4 in case of MAL-Sel strain which suggests the involvement of esterases and monooxygenases. The resistance to the AChE targeted insecticide in this pest depended on the target insensitivity and the enhanced activity of MFO and esterase. Thus, the cross resistance between pyrethroids and the AChE targeted insecticides could be resulted from the enhanced activity of MFO and esterase.