Bioactivity and volatile profiling of Azadirachta indica leaves for the suppression of Maize Weevil, Sitphilus zeamais (Motsch.) infestations (FP1017)

Abstract

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Neem (Azadirachta indica A. juss), is known to possess a wide range of pharmacological properties and is thus commercially exploitable. Apart from its medicinal potential, a considerable progress has been achieved regarding biological potential and composition of volatile fraction of the leaves which is an ever-increasing interest to th e scientific community. During this study, biological phenom ena and for the first tim e, volatile composition of A. indica leaves w ere examined in the m anagem ent of Sitophilus zeamais on stored maize. Efficacy of neem leaves was tested by admixing leaf powders with maize grains at 5 doses (3.33%, 10%, 16.67% , 23.33% , and 33.33% w /w ). Using m odified cup-bioassays, repellent effect was assessed after an hour of weevil introduction, w hile contact and fum igation toxic potential of leaf powders w ere evaluated at 24 hour intervals up to 10 days of weevil exposure. Volatile profile of A. indica leaves was characterized by employing headspace-solid-phase micro extraction coupled with gas chromatography-mass spectrom etry (HS-SPME/GC-MS). Over 60% weevil repellency was recorded at doses above 23.33% , whereas 100% and 67% contact and fum igation mortalities w ere observed respectively, 9 days after treatm en t at the dose of 33.33% . Four volatile compounds w ere identified accounting for 99.98% of the total detected constituents in three distinct chemical classes (Sesquiterpenoid, aldehyde and halogenated aliphatic hydrocarbon). G am m a.-elem ene (54.96% ) and 2-hexenal (33.33% ) w ere the m ajor constituents of neem leaf volatiles, followed by m ethylene chloride (6.05%) and caryophyllene (5.65% ) which are responsible for varied biological activities observed. Odor impact of th e bioassay-guided study clearly implies th a t A. indica leaves can be harnessed against S. zeamais infestations.