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The interest of the problem lies in the fact that Sitophilus zea-mais Motschulsky and Sitophilus oryzae (Linnaeus) are so closely related that they have only recently been separated as two distinct species. A third species Sitophilus Eranarius (Linnaeus) commonly found with them in the same habitats was also used in these experiments. A comparative study of the behaviour of the three species was carried out. The different behavioural aspects examined in the present work were the preference of the weevils for oviposition sites , some factors inducing flight, their climbing ability on glass, their reactions in different humidity gradients and in a temperature gradient, and finally their behaviour to a source of light. The behaviour of the fourth instar larvae in a horizontal beam of light and in a steep humidity gradient was also determined. The sensory organs involved in some of these mechanisms were located and described. The differences in the behaviour pattern of the three species substantiate their taxonomic separation.