Efficacy of Essential Oils Against Black Bean Aphid (Aphis fabae Scopoli) under Laboratory Conditions

The black bean aphid (Aphis fabae), poses a significant threat to cultivated crops, leading to food insecurity and hunger concerns. Essential oils from plants offer promising low-risk alternatives to synthetic chemicals for aphid control whose widespread use has raised serious environmental and health issues. To assess the efficacy of plant essential oils, an experiment was carried out at the Entomology Laboratory of Lamjung Campus, Tribhuvan University following a completely randomized design with three replications using eight treatments including a control (distilled water and ethanol). The essential oils used were Neem (Azadirachta indica), Eucalyptus (Eucalyptus globulus), Palma rosa (Cymbopogon martini), Citronella (Cymbopogon winterianus), lemongrass (Cymbopogon citratus), Juniper berry (Juniperus recurva), Mint (Mentha arvensis) and control (distilled water and ethanol) at the concentration of 1% and 2% with the exposure time of 12, 24 and 48 hours for contact mortality and 2 µL and 4 µL with the exposure time of 12 and 24 hours for fumigation mortality. The result revealed that individual mortality rate increased with increasing oil concentration and exposure time. Lemongrass with 2% concentration resulted in the high mortality percentage (66.66%) whereas, Neem with 1% concentration demonstrated the lowest (23.3%) in contact assay. Similarly, in fumigation assay, the highest mortality percentage was exhibited by 4 µL Lemongrass (100%) when compared to 2 µL Neem and Juniper berry have lowest mortality percentage (73.33%) after the control. Therefore, Lemongrass with 2% concentration for contact assay and 4 µL Lemongrass for fumigation assay was considerably more effective than other used essential oils. However, more research is necessary with locally available essential oils to assure the long-term effectiveness in field and lab conditions with different concentrations and exposure time. The result could benefit the farmer and gardener by developing essential oils as commercial products to apply natural, eco-friendly and non-toxic management method which is alternative to synthetic pesticides.