CHARACTERISTICS OF CORN-ROOTWORM INSECTICIDE GRANULES AND THE GRIT USED BY CORNFIELD BIRDS - EVALUATING POTENTIAL AVIAN RISKS

Granules of five insecticides used for Corn rootworm control (Counter 15G, Dyfonate 20G, Furadan 15G, Lorsban 15G and Thimet 20G) were characterized on the basis of size, shape (spherical to oblong), surface texture (angular to well-rounded), composition and color. The five insecticides have similar sized granules (xBAR = 0.5 or 0.6 mm). Furadan granules are the most spherical and rounded; those of Dyfonate are the most oblong and angular. Furadan granules are purplish red and composed of silica; granules of the other four insecticides have earth-tone colors and are made of clay. Because mistaking granules for natural grit is likely a route of avian exposure to granular insecticides, granule characteristics were compared with those reported for grit found in gizzards of bird species that frequent cornfields when the insecticides are applied. Mean granule sizes of the five corn rootworm insecticides are at the lower extreme of the average grit sizes found in gizzards of the cornfield bird species. Of the five insecticides, the mean surface texture and shape values for Furadan and Dyfonate granules differ most from those of the grit in birds' gizzards. Only Furadan granules arc composed of a material that birds normally use for grit, whereas granules of the other four insecticides have hues most similar to the grit consumed by cornfield birds. Knowledge of grit-use patterns and grit characteristics may be useful in modifying granular formulations to reduce avian exposure to insecticides.