Loss is defined as a measurable decrease of the food quantity and quality. Loss should not be confused with superficial damage generally due to deterioration. Quantitative loss is physical and can be measured in weight or volume, while qualitative loss can only be assessed.
Quantitative loss, qualitative loss, nutritional loss, seed viability loss and commercial loss may gauge this reduction.
The major biotic factors influencing wheat loss during storage are insects, molds, birds and rats. The major insect species known to infect wheat include Khapra beetle, Trogoderma granarium Everts; Lesser grain borer, Rhizopertha dominica (F); Rice Weevil, Stitophilus oryzae (L.) and Red flour beetle, Tribolium castaneum (Hbst). All these insects may be found extensively in most developing countries to different extremes. Other insect species are recognized storage pests that also infest stored wheat like Angoumois grain moth, Sitotroga cerealella (Oliv.); Rice moth, Corcyra cephalonica Straint; Saw toothed grain beetle Oryzaephilus surinamensis (L.); Long headed flour beetle Latheticus oryzae Wat.; Flat grain beetle Cryptolestes pusillus (Schoen).
Biotic factors including temperature, humidity and type of storage all affect environmental conditions in storage. High temperature causes deterioration, while low temperature is good for storage. High temperature accelerates the respiration of grain, which produces carbon dioxide, heat and water, conditions favorable for spoilage. Humidity equally impacts grain storage. Increasing humidity increases spoilage, while decreasing humidity is good for storage.
The type of storage plays a fundamental role in storage efficiency. If a concrete or mud storage structure can absorb water or allow the water vapors to pass through, in the case of a jute bag, the bio-chemical changes and mould attack are minimal, but the risk of insect infestation increases. Sun drying or turning of food grain has many advantages as it provides an opportunity for inspection and precautionary measures to avoid spoilage. Aeration greatly minimises mould growth, insect activity, and respiration of the seed. Further aeration provides a cooling action and equalises the temperature throughout the mass of the grain stored. Bad odors developed by stored grains can be easily and effectively removed.
Climate conditions, grain conditions at storage (presence of infestation, moisture content, foreign matter content), the period of storage, grain and pest control practices all contribute to the rate of loss caused by insects and mold growth. As these factors interact, it is difficult to isolate them or identify one factor, which has a direct influence on loss.
Direct crop losses caused by diseases and pests may be measured as the proportion of crop not sold. In addition to losses in yield and quality in the field and later during storage and transport, there are many, less tangible ways in which diseases and pests exact an economic toll.
Crop losses caused by competition from weeds can be assessed quite readily, but weeds also contribute to overall crop losses by acting as alternative hosts for pathogens and insects.
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