Indirect effects of herbicides on bird food resources and beneficial arthropods

This study examined effects of agricultural herbicides on food webs to quantify how herbicide induced changes in the plant community affect arthropod abundance. The study focused on insects eaten by ring-necked pheasant and gray partridge chicks and on beneficial arthropods that prey on insect pests and weed seeds. The experiment, conducted in 1998 and 1999 at Montana State University's Arthur H. Post Experimental Farm, contained three arable plant communities blocked against a nearby fencerow. Plants were sampled by volume measurements in 0.5 m2 rings. Ground dwelling arthropods were collected with pitfall traps, and vegetation dwelling insects were collected with a sweep net. Beneficial arthropods and vegetation dwelling, chick-food insects were more common in the weedy community than in the more monocultural communities. This study demonstrates that herbicides do affect arthropods that serve as avian food resources and as beneficial predators in a North American agroecosystem, and that these effects are most likely mediated by changes in the plant community. Management implications for beneficial arthropods, chick-food insects and game birds are discussed.