Effects of Dimethoate on Small Mammal Populations

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Abstract
The effects of an insecticide, dimethoate, on small mammal populations comprising three species, the prairie vole (Microtus ochrogaster), the house mouse (Mus musculus), and the prairie deer mouse (Feromycus maniculatus), were investigated by means of live trapping grids in an Indiana clover field. House mice decreased in numbers after spraying while prairie voles increased and deer mice remained at the same density level. Density of insects declined greatly after spraying, but no evidence was found to indicate that the insecticide caused direct mortality in any of the mammal species or had any additional effect on the habitat. It is postulated that the abrupt decline in insects was related to a drift in the mammal population composition from an omnivore to a herbivore species.