[Development of resistance in Pharaoh's ant (Monomorium pharaonis)]

The possibility of resistance development in the pharaoh's ant Monomorium pharaonis in regard to insecticides and chemosterilants in general and in the special case of sodium arsenate is discussed. The low number of sexuals and the long duration of generations reduced the possibility of the development of resistance in social insects to a great extent. Although the pharaoh's ant offers relatively good possibilities for the selection of resistance on account of the polygyny, the duration of generations in the range of a whole year under field conditions and the isogeny of the colonies diminished the development of resistance. Experimental investigations for the selection of resistance to sodium arsenate in laboratory colonies with artificially shortened sequence of generations are presented. Following six generations, no enlargement of tolerance or true resistance but a clear sensitivity could be stated. This sensitivity leads to an eradication of the colonies. It is pointed out, that in pharaoh's ant a development of resistance against the lethal action of sodium arsenate and carbaryl is impossible, because of the protection mechanism of the social food chain.