Diversity and Density of Foliage-Inhabiting Arthropods in Irrigated and Dryland Soybean in Mississippi

Abstract

The effect of irrigation on diversity and density of foliage-inhabiting arthropods was determined for late maturity, wide row soybean during a three-year study in the alluvial plain (Delta) in Mississippi. The ratio of amount of rainfall in dryland soybean to amount of irrigation and rainfall in irrigated soybean (“stress index”) ranged from 0.11 to 0.54, with canopy development reduced at the sites where rainfall was most limiting. Herbivore species richness was greater and predator evenness lower in irrigated than in dryland soybean at the most severely stressed site. The ratios of density of total arthropods, herbivores, and predators in dryland to irrigated soybean were positively correlated with the stress index over the three years of the study. Of the most common species, all showed similar response (as did order totals and trophic levels), except Heliothis spp. and bigeyed bugs, Geocoris spp., which were equally or more abundant in the dryland than in the irrigated soybean. Establishment of damsel bugs ( Nabis spp.) occurred after the canopy from adjacent rows overlapped. In the final year, early initiation of pivot irrigation resulted in earlier canopy development and was associated with synchronization of density of damsel bug nymphs and lepidopterous larvae in pivot-irrigated, but not in furrow-irrigated or dryland soybean.