"Insecticidal Activity of Essential Oil Extracts from Oregano (Oreganum vulgare), Eucalyptus (Eucalyptus globulus), and Basil (Ocimum basilicum) Against Rice Black Bug (Scotinophara coarctata) Hemipte

Abstract

INTRODUCTION

Rice infestation has always been an area of concern for rice farmers since various pests are consistently attacking their field, costing them a lot of money. Chemical pesticides have been their first resort at the expense of affectingthe quality of their harvest and harming the natural predators of their target pest. Thus, current researches are gearing toward the production of natural pesticides that are environment-friendly and will not affect the natural balance of a rice field ecosystem. As such, this study aims to determine the insecticidal activity of Oregano, Eucalyptus, and Basil Essential oils against a common rice pest, Scotinophara coarctata (Rice Black Bug).

METHODS

Oregano, Eucalyptus, and Basil leaves were gathered, washed and prepared for essential oil extraction. Wet steam distillation was done to obtain the essential oils from the leaves of plant samples. Insecticidal Assay was performed in a laboratory set-up by exposing ten (10) insects to filter papers soaked with a constant amount of essential oils (5ml) placed inside a container's lid. The time of death upon exposure to EO of all the insects (min) was recorded in each of the set-ups.

RESULTS

Based on the data gathered, Eucalyptus had the highest percent yield (%v/m) of 5%. From the results of the insecticidal assay, Eucalyptus EO is the most effective for it showed the fastest and most toxic effect on S. coarctata as reflected by the shortest recorded average time of death upon exposure to EO of the Rice Black Bug (9.37 min). Moreover, based on the ANOVA, a p-value of 0.018465 is obtained thus the alternative hypothesis is accepted and that there is a significant difference in the insecticidal activity of the different essential oils.

DISCUSSIONS

Also, the researcher obtained significant values for the different time of death upon exposure to EO of rice black bug for each set-up. This implied that the Oregano, Eucalyptus and Basil essential oils can really be a potential source of effective natural insecticide since exposure to them leads to the death of rice black bugs. Eucalyptus EO is the most effective for it showed the fastest and most toxic effect on S. coarctata as reflected by the shortest recorded average time of death of the Rice Black Bug. All the tests were conducted in vitro. Further studies on the synergetic effects of the three essential oils can also be a future topic of interest. Lastly, the researchers suggested trying the product in an open field or in an actual rice field.