Natural history of the soybean aphid on its overwintering host Rhamnus cathartica in Indiana

Since its detection in 2000, the soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae), has been a serious pest in cultivated soybean Glycine max, (L) Merr. The soybean aphid has a heteroecious holocyclic life cycle, alternating between hosts for sexual reproduction. The annual alternation involves a primary host (Rhamnus cathartica) used for sexual reproduction and a secondary host (soybean) colonized by parthenogenetic morphs. Eggs of the soybean aphid are deposited on the margins of buckthorn buds where they overwinter from October to early April or when optimal hatching conditions are reached. To determine abundance, rates of survival and sources of mortality of the soybean aphid on its overwintering host in Indiana, studies were conducted from October, 2006 to March, 2009. To determine effects of predation on buckthorn, the survival of caged and exposed soybean aphid eggs was recorded throughout fall and spring. Mortality rates were high in both locations. Sources of this mortality were both biotic and abiotic in nature. Exposed eggs experienced greater mortality (85%) than eggs protected with cages (55%). Biotic mortality due to predation was most prevalent in the fall. During the winter in the absence of predators, the mortality rate continued to increase due to abiotic factors. Predators arrived to R. cathartica as soon as soybean aphid migrants, lowering the population to undetectable levels. The ability of this study to link the predator prey cycles observed on both soybeans and R. cathartica in Indiana supports the importance of including biological control into decision management tools.