This time last year, many towns and cities in Indiana and Illinois experienced incredibly large swarms of soybean aphids. This year (2010), I have seen a few soybean aphids but nothing like the massive clouds that choked joggers and interfered with baseball games. Interestingly, the soybean aphid follows a 2-year cycle. Odd years have the largest populations and even years have lower populations. This may be due to predator-prey cycles, with high summer populations of aphids producing high predation on subsequent overwintering populations.
The soybean aphid is an invasive species that is native to Asia. The soybean aphid arrived late last century and was first discovered in July of 2000. The soybean aphid spends summers on soybean, but overwinters on buckthorn, a non-native invasive species.
When soybean aphid first arrived in the US, my late colleague, Bob O’Neill and I drove all over Tippecanoe County looking for buckthorn trees that might serve as overwintering sites, especially trees that might be located on our research farms. No luck. We were chagrined a few days later when walking back from our motor pool, I discovered that the gravel pit next to campus was covered by large populations of buckthorn. We later found some buckthorn trees on campus less than a block from our Department.
Until the arrival of soybean aphid, it was rare for soybean growers to treat their crops with insecticides. However, soybean aphids can reach thresholds of 250 aphids per plant in scattered fields forcing growers to spend time and money monitoring and treating the pests.