Does agricultural landscape complexity affect soybean aphid suppression in Manitoba?

Movement of transient generalist predators into soybean fields is crucial for controlling soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). We hypothesized that the structure and composition of agricultural landscapes affect the level of soybean aphid biological control observed in Manitoba. We studied soybean aphid suppression in 27 fields across a gradient of landscape complexity during 2013 and 2014.

In each field we infested potted soybean plants with soybean aphids (14 aphids / pot) and treated them as 1) open to predation by ambient levels of natural enemies versus 2) protected from predation by predator exclusion cages. This design was replicated five times in each soybean field. Surrounding habitats within a 2 km radius of each selected soybean field were mapped and digitally quantified using ArcGIS 10 to characterize landscape complexity.

Soybeans, cereals, and canola were the major land-cover types found across landscapes. Proportion of cereal crops had a negative relationship with soybean aphid survivorship in the open treatment at various scales. Naturally occurring aphid populations were negligible during both years. Our results suggest that incipient aphid colonies in soybeans may be subject to high levels of predation in landscapes dominated by cereal crops, where predators can find alternative aphid species to support their populations.