Experimental aerial spraying by Butcher (3), Butcher and Eaton (4) and Peterson (7) has been described; but potency tests of the synthetic organic insecticides against the larch sawfly, Pristiphora erichsonii (Htg.), have not been reported.
The first screening tests were carried out in 1955 at Cass Lake, Minn., with DDT, chlordane, methoxychlor, benzene hexachloride (BHC) and malathion against larvae of each of the five different instars. High temperatures in the field laboratory killed an inordinately large proportion of the control insects, making interpretation of the test data hazardous. Examination of the data indicated that BHC and malathion were the only promising toxicants. Work was continued by the author at Cass Lake in 1956 with these insecticides as well as with DDT, which has been used frequently against forest defoliators.