Egg survival and seasonal phenology of the soybean aphid on its overwintering hosts in Indiana

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), a key pest of soybeans, has an heterocious holocyclic life cycle and utilizes species in the genus Rhamnus as primary hosts. Three species of Rhamnus have been reported as functional hosts for the aphid; Rhamnus cathartica L., Rhamnus alnifolia, L’Hériter and Rhamnus lanceolata Pursh. Of the three species R. cathartica has been reported to be the most abundant. The eggs of the soybean aphid are deposited on the margins of the buds of the primary hosts and overwinter from October to late March or when warmer and optimal conditions are reached. Rates of survival and sources of mortality on these overwintering hosts are not well known. Studies were conducted from October of 2006 to October of 2008 in two Indiana locations on R. cathartica to monitor the abundance and survival of the soybean aphid eggs. To determine effects of predation, caged and exposed treatments were set up in these locations and survival of soybean aphid eggs throughout fall and spring was observed and recorded. Predator abundance, hatching dates, temperature and phenology was measured as well in both locations. High rates of mortality (greater than 70%) were recorded in both locations throughout the experiment in caged and exposed treatments. Very few predators were caught, indicating that most of the mortality was due to abiotic factors.