what are post harvest losses?

Post harvest losses refers to the loss of food product after it has been harvested form the crop field. It includes loss in the quantity of the food product produced and also a loss in its quality. It may be due to contamination ,attacks by rats, birds, and other pests, insect damage and infestation by food-borne pathogens. 

Genetically modified crops have reduced post harvest losses as they are resistant to insects, pest or pathogen and there is very less loss of nutritional value in these crops.