There are three major reasons why rats and mice are considered pests:
They consume and damage human foods in the field and in stores. In addition they spoil it in stores by urine and droppings reducing the sales value.
Through their gnawing and burrowing habit they destroy many articles (packaging, clothes and furniture) and structures (floors, buildings, bridges, etc.). By gnawing through electrical cables they can cause fires.
They are responsible for transmitting diseases dangerous to man.
It is impossible to put an exact estimate on these losses, but it is obvious that the damage caused by rodents is enormous.
Diseases transmitted by rats to man pose a serious public health problem in tropical countries. Apart from causing human suffering, they are responsible for financial losses incurred through work-days lost and additional medical bills.
While this topic is not directly related to post-harvest problems, it bears relevance to post harvest rodent control. As rodent pests in stores and households are controlled the rate of disease transmission will be reduced.
Just as it is difficult to put exact figures on losses caused by rodent pests, it is not easy to estimate the exact benefits of rodent control. However, it is apparent that rodent control is mostly if not always cost effective.
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Rodent Species of Post-Harvest Importance
There are more than 4000 species of mammals, of which about 1700 are rodents. The rodents’ family MURIDAE contains the most species, of the genus Rattus. However, not all the 1700 rodent species are pests.
About 150 species have been defined as pests at some localities to some crops at some time or another, but only 20 could be termed important. Very few species indeed are regularly described as pests in the literature.
In connection with post-harvest losses, the number of species occurring in and around human habitation drops to below ten.
Of these, three species are found throughout the world: the house mouse (Mus musculus), the house or roof rat (Rattus rattus) and the brown rat (R. norvegicus).
The multimmate rat (Praomys natalensis) and the spiny mouse (Acomys cahirinus) are found in Africa; while the Pacific rat (R. exulans), and the bandicoot rat (Bandicota bengalensis).
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