Effects of agroecosystem diversification on natural enemies of soybean herbivores

This study evaluated the effects of agroecosystem diversification through no‐tillage and strip intercropping on the abundance of natural enemies of soybean (Glycine max Merrill) herbivores. Twenty‐four plots (289 m2 each) were arranged in a randomized complete block design for a 3 by 2 factorial experiment. Factors were cropping systems (corn monoculture, soybean monoculture, and strip intercropping of corn and soybean) and tillage systems (no‐tillage and conventional tillage). Natural enemies were sampled during 1988, 1989 and 1990 by sweep net, suction net (D‐Vac), pitfall traps and quadrat samples. Analyses of variance indicated that of 15 taxa analyzed, most foliage‐inhabiting natural enemies were significantly more abundant in intercropping than in monoculture plots, whereas soil‐inhabiting natural enemies had higher numbers in no‐tillage plots than conventional tillage plots. Therefore, the results support the theory of greater abundance of natural enemies in more complex agroecosystems. Better environmental conditions in diversified treatments was the possible reason for these results. Corn in intercropping plots provided shade, reduced wind speed, alternate food, and possibly higher humidity and lower temperatures for soybean natural enemies. A similar effect was likely caused by the stubble and weeds in no‐tillage plots.