Wildlife Effects from Grasshopper Insecticides Sprayed on Short-Grass Range

Insecticides were sprayed experimentally at several sites on short-grass plains vegetation by the Agricultural Research Service (ARS), United States Department of Agriculture (USDA), to determine effectiveness for grasshopper (Acrididae) control. Effects of the applications on resident wildlife were studied by the Denver Wildlife Research Center. Observations were also made on the effects of an operational range caterpillar (Hemileuca oliviae) control program with toxaphene. Direct effects on birds varied widely with the chemicals applied, spray rates, and conditions. Applications (in ounces of active ingredient per acre) that killed birds and resulted in significant population decreases were: Fenitrothion (9.6 oz), BAY 77488 (4.6 and 9.3 oz), diazinon (5.0 to 8.0 oz), and toxaphene (16 oz). Applications that resulted in significant population decreases under some conditions, but without any observed bird mortality, were: Fenitrothion (6.3 oz), Baygon (3.0-4.0 oz), and Guthion (4.0 oz). Applications without observed direct effects on wildlife were: BAY 77488 (2.5 oz), carbaryl (6.4 oz), malathion (6.8 oz), and Mobam (3.0 oz). Registration and use of pesticides for range grasshopper control should be limited to those that degrade rapidly in the environment, have the least direct impact on wildlife, and have been thoroughly field-tested.