Spatio-temporal distribution of corn leaf aphids (Homoptera: Aphididae) and lady beetles (Coleoptera: Coccinellidae) in Iowa cornfields

Preyâ€"predator interactions are spatially and temporally dynamic and influenced by environmental factors. Field studies were conducted to investigate the dynamics of spatio-temporal interactions among corn leaf aphids, lady beetles, and environmental factors in cornfields by mapping and comparing their distributions. Lady beetle species in this study included Harmonia axyridis Pallas, Coleomegilla maculata (DeGeer), and Coccinella septempunctata L. A global positioning system, geostatistics, and a geographic information system (GIS) were used to locate sample points, characterize distribution patterns, and map the distributions of corn leaf aphids, lady beetles, and environmental factors. Geostatistical analysis showed that both corn leaf aphid and lady beetle populations were aggregated during the peak population period and randomly distributed early and late in the season. Map-correlation analysis, however, showed that the distribution of lady beetles did not always coincide with that of corn leaf aphids. The results also showed that none of the environmental factors we sampled were significantly correlated with corn leaf aphid and lady beetle distributions. This study documents the dynamic relationships in time and space between lady beetles and corn leaf aphids.