Hyposidra talaca Walker is a major defoliating pest of the tea plantations in the Terai region of Darjeeling foothills, West Bengal, India. A huge array of chemical pesticides, including cypermethrin (synthetic pyrethroid), are regularly used to control this geometrid pest in the tea plantations of this region. Indiscriminate use of chemical pesticides induces increasing level of tolerance to pesticides in the pests leading to control failure. Some entomopathogens of this looper pest including nucleopolyhedrovirus (NPV) have been studied to determine the potency of these agents as biopesticides. For effective pest management strategy, the information regarding the toxic effects of sub-lethal concentrations of cypermethrin and HytaNPV on H. talaca at their cellular, biochemical and enzymatic levels is the needs of the hour. Therefore, in the present investigation, mid-lethal concentrations of cypermethrin and HytaNPV were determined in Hyposidra talaca larvae reared on artificial diet by dietincorporation and diet-coating methods, respectively, for three successive days of exposure at 24 h interval. LC50 of cypermethrin for 48 h exposure showed steep decrease from that of 24 h exposure, but showed little difference with 72 h exposure. It indicated immediate action of cypermethrin, a neurotoxin, on the larvae. For NPV, the estimated LC50 values for 24 and 48 h exposure revealed very little difference, whereas, at 72 h exposure the LC50 value declined steeply from the earlier values. It supports the delayed action of NPV on the larvae.