Insecticidal Potential of Essential Oils against Tribolium castaneum (Herbst.)

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INTRODUCTION
Insects are of great economic importance they are both useful and harmful to man.Across the world, a staggering count of over 10,000 insect species have been documented as culprits causing substantial harm to stored grain products.(Rajendran and Sriranjini, 2008).A pest refers to any creature whose population, when it exceeds a certain threshold, can lead to economic harm, creating a clash with human well-being, convenience, and financial gain.Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) holds a crucial status as an insect pest that significantly impacts food grains, earning its reputation as a primary adversary in stored grain ecosystems (Howe, 1965).As per FAO's assessment, pests infesting stored grains have been wreaking havoc on food supplies.Each year, an estimated 10% to 25% of the global harvest is lost due to the destructive impact of insect and rodent pests, with instances even reaching an alarming 80%, as documented by reports (Matthews, 1993;Dwivedi and Shekhawat, 2004).The pest is generally found in grain storages, flour mills, and warehouses.Wheat is global crop, serving as a primary protein source in impoverished and developing nations.Proper storage is crucial during transportation and throughout the year to safeguard grains from pests, especially in hot and humid summer months when crops aren't grown (Khalil, F. M. A et al., 2022) The management of these insects heavily depends on the utilization of synthetic insecticides and fumigants; however, the extensive application of these agents has given rise to significant challenges, notably the emergence of insect strains that have developed resistance to insecticides.(Dubey, et al, 2008) Higher plants offer a wealth of unique natural compounds that hold the potential to foster the creation of ecologically sound approaches for insect management, as highlighted by Jbilou, et al., 2006.Plants naturally synthesize secondary metabolites, a considerable portion of which serve as innate defences against both insects and pathogenic microorganisms (Potenza et al. 2004).Plant-derived compounds exhibit not only a high level of safety for endothermic organisms but also demonstrate enhanced biodegradability, coupled with reduced susceptibility to insect resistance (Oparaeke et al., 2005).
Azadirachta indica A. Juss (Meliaceae), commonly known as Neem, boasts a plethora of valuable compounds, notably azadirachtin and tetranortriterpenoid limonoids, which play pivotal roles as active ingredients in numerous neem-based insecticides, as noted by Mordue and Blackwell in 1993.Every facet of the neem plant, particularly its seed oil, harbours antifeedant, repellent, growth-disrupting, and larvicidal attributes, effectively countering a diverse range of pests.(Chaudhary, S. et al., 2017 Neem oil exhibits a promising efficacy against Tribolium castaneum.Mustard essential oil, along with its prominent constituent allyl isothiocyanate, exhibits remarkable fumigant toxicity against insects infesting stored grains.Notably, mustard oil encompasses glucosinolate, recognized for its anti-carcinogenic qualities, effectively impeding the formation of cancerous tumors, and showing promise for controlling stored grain insects.Furthermore, the application of mustard oil leads to mortality in both larvae and adults of these stored grain pests.(Attia A. et. al., 2014;Worfel et al., 1997;Paes J. et al. 2011).With the aim of finding eco-friendly alternatives to conventional pesticides for controlling storage insects, the present study was designed to experiment with essential oils from Azadirachta indica (neem) and Brassica juncea (mustard), two potential medicinal plants renowned for their pesticidal properties.

MATERIALS AND METHODS
Tribolium castaneum, commonly known as the red flour beetle, was collected from infested wheat grains.The collected cultures were then reared and maintained in laboratory conditions at 25±1ºC and 65±5% relative humidity.For the toxicity assay, both adult beetles and fourth developmental stage larvae were utilized.
Neem (Azadirachta indica) and Mustard (Brassica juncea) essential oils were procured from R. V. Essential Delhi.To attain the desired concentrations, the essential oils were meticulously dissolved in acetone, resulting in the preparation of the necessary solutions.

Larvicidal Bioassay:
An experiment was designed to determine the LC50 value of the effect of A. indica and B. juncea oils on fourth developmental stage larvae.A range of dilution percentages, specifically 10%, 12%, 14%, 16%, 18%, and 20%, were subjected to testing.Control larvae were kept under the same condition mixed with acetone but without any essential oils.All tests were replicated five times.The mortality rate of treated larvae was calculated after 48 hrs.LC50 was calculated by using log probit analysis.

Adulticidal Bioassay:
Adulticidal bioassay experiment was designed to determine the lethal concentration (LC) value of the effect of A. indica and B. juncea oils on adult T. castaneum.Twenty adult beetles were released into a jar containing thirty grams of wheat grains treated with various dilutions (21%, 23%, 25%, 27%, and 30%) of A. indica and B. juncea oils.The data collected from this experiment underwent thorough log probit analysis.

RESULTS AND DISCUSSION
To assess the lethal effects of A. indica and B. juncea oils on fourth developmental stage larvae and adults of T. castaneum, toxicity experiments were performed.The results revealed positive toxic effects of these essential oils on the overall mortality of both larvae and adults of T. castaneum.Toxicity effects on the fourth developmental stage larvae were assessed at different concentrations of A. indica and B. juncea oils, resulting in an LC50 value of 13.47% for A. indica and 17.67% for B. juncea (Table 1).The adulticidal activity of A. indica and B. juncea showed LC50 value at 22.91% and 25.16% (Table 2) concentration respectively against adult T. castaneum.As the concentration of oils increases the mortality also increases simultaneously.Tables 1 and 2 present the 95% confidence intervals and regression coefficients obtained from larvicidal and adulticidal bioassays carried out using the essential oils extracted from A. indica and B. juncea, in relation to their effects on T. castaneum.In Figures 1a and 1b    There is a growing interest among scientists in studying the bioactivity of plant essential oils and extracts against stored-grain insect pests.(Dubey et al., 2008;Benzi et al., 2009;Padin, S. B et al., 2013).In this investigation, Azadirachta indica and Brassica juncea oils demonstrated significant potential as insecticidal agents against T. castaneum.The insecticidal activity showed variations depending on the concentrations of the oil and the duration of exposure.An observed correlation between dose and response was evident, as larval and adult mortality increased while larval survival and adult emergence declined with rising concentrations of the essential oil by Scott et al., (2003); Upadhyay and Jaiswal, (2007); Kraikrathok et al., (2013) same was stated by the experiment conducted with A. indica and B. juncea against T. castaneum.Azadirachta stands out as a crucial plant-derived compound in the realm of insect pest management.Its remarkable trait of low mammalian toxicity and its compatibility with beneficial insects make it a standout choice, as highlighted by Schmutter in 1990.It has mainly antifeedant effects (Zehnder and Warthen, 1988;Schmutterer, 1990) and is an insect growth regulator (IGR) property.
, the 95% confidence intervals and regression coefficients are depicted, specifically highlighting the larvicidal activity of A. indica and B. juncea essential oils against T. castaneum larvae.Figures 2a and 2b also illustrate the 95% confidence intervals and regression coefficients, focusing on the adulticidal bioassays involving A. indica and B. juncea essential oils against T. castaneum adults.Table 1.Effect of A. indica and B. juncea on 4 th instar larvae of T. castaneum.

Figure- 2
Figure-2: a & b: Regression line of probit mortality of T. castaneum against E. oils of a.-A.indica.b-B.juncea.

Table 2 .
Effect of A. indica and B. juncea against Adult of T. castaneum