Within-plant distribution impacts cabbage aphid (Brevicoryne brassicae) reproductive potential on winter canola

The cabbage aphid (Brevicoryne brassicae) is a perennial pest that specializes on plants of the Brassicaceae family. Feeding damage observed in winter canola (Brassica napus) can result in seedling death, curling, yellowing, stunting, or virus transmission; all of which can alter seed quality and reduce yield up to 33%. The cabbage aphid attacks canola before and during flowering, typically colonizing the new growth areas of the plant or the upper flowering canopy. This colonizing behavior can be induced by intrinsic characteristics of the host plant (bottom-up effects) such as nutritional value, secondary compounds, morphology, or plant architecture. However these considerations and their relationship to cabbage aphid population dynamics need further study. Therefore, our goal was to evaluate how within-plant distribution impacts cabbage aphid reproductive potential on different canola plant structures. Specifically, we restricted aphid localization using two types of exclusion cages. Cages enclosed either the flowering raceme, or a single leaf in the lower canopy. Each cage was inoculated with two, newly-reproductive adult cabbage aphids. This study was replicated in the field at Ashland Bottoms Research Farm near Manhattan, KS and in plants grown under controlled greenhouse conditions. Aphid populations remained in all exclusion cages for 3 wk before they were removed; plant material was bagged and aphid densities were recorded in the laboratory. Preliminary results suggest that within-plant distribution of the cabbage aphid directly affects aphid population density with higher growth rates observed on reproductive canola structures. Direct implications for pest management and sampling plans will be discussed.