Pests and their natural enemies on soybean and corn grown in diversified systems

Abstract

Intercropping and no-tillage systems can affect the population dynamics of insects, increasing or decreasing the population density of pests and natural enemies. The objective of this study was to evaluate the effects of no-tillage and strip intercropping of soybean [Glycine max (L.) Merrill] and corn (Zea mays L.) on the abundance of insect pests and their natural enemies. Plots were arranged in a randomized complete block design in a 3 x 2 factorial experiment (soybean monoculture, corn monoculture, strip intercropping of soybean-corn under no-tillage and conventional tillage). Insects were sampled using sweep net, ground cloth and by visual search. For corn, the occurrence of insect pests and predators was not affected by soil management practices. Larvae of Helicoverpa zea occurred in higher number (5.1) for corn under strip intercropping. For soybean, adults of Anticarsia gemmatalis and of the predator Cycloneda sanguinea were more abundant for the no-tillage plots, respectively, 0.4 and 2.4 insects. A higher number of the syrphid Toxomerus sp. was observed for the conventional tillage plots (1.3). Under strip intercropping conditions, low numbers of Diabrotica gracilenta (11.5) were observed, while Maecolaspis sp. (5.0) and Megascelis sp. (17.0), and the predators C. sanguinea (2.3), Doru sp. (0.8), Geocoris sp. (1.5) and Toxomerus sp. (1.4) occurred in high densities.