Evaluation of insecticidal and repellent effects of Mentha x piperita and Cymbopogon citratus on economically important stored grain against Tribolium castaneum (Red flour beetle)

Abstract

The excessive use of synthetic insecticides poses serious damage to the environment, crops, and human health. These chemical control strategies lead to resistance to pests, environmental contamination, human intoxication, and toxic residues in the food. Due to these alarming issues, the natural insecticides of botanical origin have attracted arch interest in these recent years as eco-friendly alternatives to their synthetic pesticidal ancestors. These are biodegradable, reduce crop losses, are environmentally friendly, and are much cheaper than conventional pesticides. Plant extracts have several bioactive compounds that are tremendously fruitful for plant defense against insect pests. The prime objective of this study was to evaluate the insecticidal and repellent effects of leaf extracts of two plants i.e., Mentha x Piperita and Cymbopogon citratus against the worldwide pest of the stored products Tribolium castaneum, and to conduct the qualitative analysis for the screening of active chemical compounds present in both the extracts. Mortality and repellent assays were conducted using different concentrations of the extract and results were evaluated at different periods of exposure. LT50 for both extracts was also calculated to estimate the time required by both extracts to kill and repel 50% of the target pest. As per the data obtained, the relationship between exposure time and extract concentration on mortality and repellency of target pest indicated that mortality was increased by increasing the extract concentration and exposure time, and it also differed from one plant to the other. Mentha x Piperita proved to be a better repellent than Cymbopogon citratus exerting a percentage mean repellency of 80 ± 0%, 87 ±11.5%, and 100 ± 0% at 1.5%, 2.5%, and 3.5% concentration treatment at 75 mins of exposure period. On the contrary, Cymbopogon citratus methanolic extract proved to be a better insecticide than that of Mentha x Piperita because of its earlier response against T.castaneum at every concentration applied. 5%, 10% and 15% of concentration treatment of lemongrass exerted 86.7 ± 5.77%, 96.7 ± 5.77%, and 100 ± 0% percentage mean mortalities respectively after 30 hours of exposure. Additionally, the preliminary phytochemical screening as a qualitative identification of chemical groups also confirmed the presence of terpenoids present in both the sample plants, which happen to be major constituents acting against Tribolium castaneum. The results of the study provided sufficient scientific support for preliminary screening bioassays using natural xv plant products in the form of extracts as control agents rather than synthetic ones to minimize the resistance mechanism, pesticide intoxication, and environmental toxicity. These plants in the form of botanical insecticides can fit well in the Integrated Pest Management programs designed for the control of various pests causing losses in food commodities.