In recent years, the Argentine Stem Weevil, Hyperodes bonariensis Kusch. (frontispiece) has been found to be a very serious pest of pastures, cereals and brassica crops throughout the high fertility areas of New Zealand. Larval stem-boring predominantly, causes major reductions in production from these pastures and crops. In the absence of any known effective biological controlling agent in New Zealand or its continent of origin, South America, an insecticide program seems to be the only feasible controlling method of the weevil in the foreseeable future. Few toxicological studies have been made with the weevil. The main objective of the work recorded in this thesis was to develop a topical application method of insecticide screening on the weevil. When this was done the aim was then to screen a series of selected insecticides on the weevil and formulated recommendations for further field evaluation of the most promising of these.