Knockdown and Toxicity of Essential Oils from the Rhizome of Zingiber officinale (L) and the Bud of Syzygium aromaticum (L) to Periplaneta americana (L)

Abstract

The American cockroach (Periplanata americana) is an important peridomestic pest that is responsible for the mechanical transmission of several disease pathogens. This study aimed to evaluate the knockdown and toxicity effects of ginger (Zingiber officinale) and cloves (Syzygium aromaticum) essential oils against Periplanata americana. Oils were extracted from the rhizomes and buds of ginger and cloves plants respectively. The oils were extracted using the hydrodistillation method and were serially diluted in 20% tween 80 solution to obtain seven concentrations (5, 10, 25, 50, 100, 200 and 400μl/ml). Whatman No.1 filter paper was smeared with 1ml of each concentration of the oil and allowed to dry. Adult P. americana were exposed to the treated filter paper in a glass jar. Each experimental set up and the control had 20 adult cockroaches each. The control experiment had the cockroaches exposed to 1ml of 20% tween 80 solution. Each experiment was replicated 4 times. The knockdown effect was observed at 10 minutes intervals for 60 minutes while the mortality count was recorded after 24 and 48 hours. After 20 minutes of exposure to cloves oil, 100% knockdown was observed in the highest concentration (400μl/ml). For ginger oil, complete knockdown was observed in the highest concentration (400μl/ml) after 30 minutes of exposure. Both ginger and clove oil showed increased mortality as the concentration increased. After 48 hours of exposure, 100% mortality of adult P. americana were recorded in both oils at the highest concentration of 400μl/ml. While 25% and 40% mortality recorded at the lowest concentration of 5μl/ml for ginger and clove oil respectively at 48 hours. There was no mortality recorded in the control. Clove oil was more potent than ginger oil, this was judged by the 48 hours LC50 value of 7.344μl/ml while the 48 hour LC50 value for ginger oil was 56.564μl/ml. It was concluded from the study that both ginger and clove oils exhibited significant knockdown and toxicity activity against P. americana. Thus, it is recommended that the essential oils from these plants should be incorporated in the production of botanical pesticides for the management of P. americana, which is a well-known mechanical vector and common household’s pest.