Neem oil derived volatiles: A natural strategy to protect black gram (Vigna mungo (L.) hepper) seeds from pulse beetle infestation during storage

Abstract

The seeds of the black gram tend to be very vulnerable to infestation by pulse beetles during storage, and this causes massive losses mainly on the quality and economic value. Existing approach methods like the use of neem oil or castor oil treatment have practical restrictions, whereas neem oil treated pulses seeds can become rancid when kept long term storage, chemically engineered fumigants have environmental and human health concerns. This current study proposes a new approach wherein the neem oil transforms into fatty acid methyl esters (FAMEneem oil) to enhance the emission of the volatile organic compounds into fumigation applications. The VOC profile of FAME-neem oil and raw neem oil were examined through Gas Chromatography Mass spectroscopy analysis. Further the bioassays confirmed fumigant and contact toxicity potential of the FAME-neem oil against pulse beetle. In the fumigation and followed by seed storage experiment, seeds fumigated with FAME-neem oil at 15 mL/kg seeds was the most effective method of retaining the quality of the seeds during storage. Black gram seed storage up to four months indicated that 0 % damage was observed on the seeds fumigated with FAME-neem oil as contradict to 7 % and 25 % damage on raw neem oil and untreated controls respectively. FAME-neem oil was able to mobilize a wider array and increase concentrations of VOCs, which allowed entry into insect tissues and the speed of insect mortality. Although this study did not assess the chemical stability of FAME-neem oil, the enhanced VOC release contributed to improved pest management performance. The results suggest that FAME-neem oil forms an efficient, ecofriendly substitution to conventional chemical fumigants and is a viable solution towards the long run preservation of black gram both for sowing and consumption purpose.