Evaluation of the insecticidal activity of Acorus calamus rhizome and Chrysopogon zizanioides roots essential oils against mealybug, Phenacoccus solenopsis

The mealybug, Phenacoccus solenopsis, a polyphagous insect pest, is considered a destructive pathogen and has invaded almost all parts of the world. The main aim of the study is to extract essential oil from Acorus calamus rhizome and Chrysopogon zizanioides roots against P. solenopsis. The essential oils were subjected to an in vitro toxicity analysis on the second and third instar stages of papaya mealybugs. At 10 μL/mL, A. calamus showed 33 ± 1.2% mortality after 24 h, and it was high (61 ± 1.7% mortality) at 50 μL/mL essential oil (p < 0.01). The combination of A. calamus and C. zizanioides essential oils exhibited a lower LC₅₀ value than individual essential oils and revealed a synergistic effect. The essential oils inhibited the expression of acetylcholinesterase and glutathione-S-transferase in mealybugs and were dose-dependent (p < 0.05). The mealybugs were exposed to different concentrations of A. calamus rhizome, roots of C. zizanioides, a mixture of these two essential oils, imidacloprid (the positive control), and water (the negative control). The amount of total protein content was 0.47 ± 0.01 µg/g in the control animals, and it was reduced in the essential oil (A. calamus)-treated mealybug (p < 0.01). Similarly, the essential oil of C. zizanioides treated mealybugs showed reduced carbohydrate (p < 0.01) and lipid content (p < 0.05). The 2nd and 3rd instar stages of mealybugs were used to inoculate papaya trees. The spray treatment was used to analyze the effect of essential oils on the mealybug population. After 24 h treatment, 1.25% A. calamus induced 47 ± 1.2 mortality and was increased to 49.5 ± 0.4% after 72 h. The mortality increased with an increasing concentration of essential oil spray than treatment time (p < 0.01). The combination of these two essential oils improved mortality more than individual essential oils revealed synergy (p < 0.01). The present finding provides for the use of essential oils to control mealybugs in papaya plantations, and the application of eco-friendly pesticides could reduce the usage of synthetic pesticides.