Perception about spoilage of food grains due to infestation differs widely amongst the scientific community and figures as high as 50% are some times quoted as the extent of loss to the predators due to inefficient management of agriculture and storage of grains. The estimates of grain production reported by various countries and compiled by FAO refer to what is harvested and it is any body's guess as to how much of this reaches the consumer's table. World food grains production was 2.136 billion tons in 2007 and only 60% was available for consumption as food while 36% was used for seed purpose and 3% for bio-fuel production. Considering that the population is growing at about 2% annually, food production will have to keep pace to avoid scarcity and famine. By using scientific technologies, wastage due to infestation has been cut down significantly but the problem of pesticide residues posing high health hazards may see progressive elimination of many of them for use in food protection systems. The most recent warnings came from a respected international group of endocrinologists that some of the pesticide residues act as endocrine disruptors which have effect on the reproduction systems of both females and males besides causing such dreaded diseases as breast cancer, prostate cancer, neuroendocrinology, thyroid metabolism and obesity.
There are systemic insecticides, contact insecticides, inorganic pesticides, natural insecticides, organic insecticides and biological pesticides, many of them permitted in many countries. Organochlorine compounds like aldrin, chlordane, endosulfan etc are highly poisonous and their continued use is increasingly being frowned upon. Organophosphates like chlorpyriform, dimethoate, malathion etc are very effective against many insects but their indiscriminate use is contaminating water sources posing potential threat to human beings. Carbamates like carbaryl, carbofuran etc are comparatively less toxic but still face opposition from environmentalists because of pollution problems when used on a large scale. Pyrethroids like cypermethrin are relatively less harmful and are commonly used in crop protection. Neonicotinoids based on nicotine, plant derived protectants like asimina from papaya seeds, azadirachdin from neem, cinnamyl acetate, pyrethrum are all available options though they are not as effective as synthetic insecticides. Biological insecticides based on the bacteria B. thuringiensis, fungi Metarhizium anisopliae, nematode Steinemema felliae, virus Cydia pomenella granulovirus are receiving attention as possible alternative protectants to chemicals.
For storage of food grains beyond 3-4 weeks, three synthetic chemicals are widely used which are Phosphine, Methyl Bromide (MB) and Sulfuryl Chloride (SC). While Phosphine may take a few days to a week to get satisfactory results, MB accomplishes satisfactory disinfestation in a day or two. Being an ozone depleting material, MB use is being discouraged in many countries and as per the Montreal Protocol it is going to be phased out. SC is the new star being promoted as a clean fumigant as its life time was thought to be just 5 years. It can also kill most of the grain infesting insects and their larvae within a day or two. But recent reassessment of its life time indicates it could be 8 times more than what was previously thought and it has 4800 times more potential as a heat trappping gas compared to CO2 casting a shadow on its wide scale use. CO2 at concentrations above 40% and Nitrogen containing less than 1% oxygen are also possible future choices provided their application logistics become practical and economical. Use of exhaust gases from internal or external combustion which contain about 12% CO2 is another option being looked into. Rice weevil, grain borers, flour beetle, grain moths, meal worms etc pose big challenges in terms of their control and elimination and if food grain stocks are to be maintained at prime condition for distribution and long term food security, use of insecticides is inevitable with their attendant consequences.
Pyrethrum from chrysanthamum flowers, Limonin from citrus peel, Spinosad, a secondary metabolite from Saccharopolyspoia spinosa, Deltamethrin, a synthetic pyrethroid and piperyl butoxide are some of the so called 'green label' pesticides, being considered especially for organic food preservation. Salt water Diatomaceous Earth (DE) is another promising natural silica based grain protectant with considerable promise. Neem oil based pesticidal preparations have become prominent now though dosage considerations are not favorable for their large scale application. Indiscriminate application of highly toxic synthetic pesticides at the farm level and fumigants at the storage level is a serious concern facing humanity and a global consensus needs to be evolved to tackle this life threatening practices without compromising on the objective of increasing food availability to the growing population.