Investigation of the lethal effects of tobacco (Nicotiana tabacum ), tombak (Nicotiana rustica ) and thyme on tobacco aphid (Myzus nicotianae ) in the laboratory conditions

Tobacco aphid (Myzus nicotianae) is an important pest affecting the quantity and quality of tobacco products which may cause pesticides application inevitable. Today, due to the emergence of pests resistant to chemical pesticides and their adverse effects on the human health and environment, it is a mandate to reduce the use of chemical compounds in pest control. In this regard, the use of botanicals such as plant extracts and essential oils are recommended as safe alternatives to the chemical pest control measures. In the present study, the effect of tobacco (Nicotiana tabacum), tombak (Nicotiana rustica) and thyme extracts were investigated on tobacco aphid. The bioassay tests were accomplished under a complete randomized design with four replications at 25 ± 1 °C, 65 ± 5% RH and a photoperiod of 16:8 hours L:D. The percentage mortality was calculated for five concentrations (6000, 8000, 10000, 15000, and 20000 ppm) of each plant extract at 24, 48 and 72 hours post application. According to the results, the pest mortality increased with the increasing concentration of plant extracts and elapsed time after treatment. The highest mortality rate (100%) belonged to tombak extract with a concentration of 20000 ppm and the lowest rate (56.75%) was observed in thyme extract at 6000 ppm concentration, respectively. The LC50 values of tobacco, tombak and thyme extracts were 12463, 10210 and 17385 ppm on the tobacco aphid tested population, respectively, showing the greater effect of the tobacco extract compared with that of other extracts.