The effect of within-plant distribution on the reproductive potential of aphids (Hemiptera: Aphididae) on winter canola (Brassica napus)

Winter canola production in the south-central US is commonly attacked by three species of aphids, Lipaphis erysimi (turnip aphid, TA), Myzus persicae, (green peach aphid, GPA), and Brevicoryne brassicae (cabbage aphid, CA), which can cause up to 33% yield loss. These aphid species vary in their biology, performance, vertical distribution within the plant and temporal dynamics across the growing season. Colonizing behavior of these aphids may be affected by intrinsic characteristics of the host plant (bottom-up effects), such as nutritional value, secondary compounds, or plant architecture. Understanding these bottom-up effects may be important in the management of these aphids in canola systems. Therefore, the goal of this research was to evaluate how within-plant distribution impacts TA, GPA, and CA reproductive potential on different canola plant structures. In field and greenhouse study (2011), five adult aphids (L. erysimi, M. persicae, and B. brassicae) were inoculated and caged onto single plants in two treatment locations: aphids restricted to the upper flowering canopy, or aphids restricted to a single leaf in the lower canopy. Population growth of each species was assessed over a three-week period. We found that growth rates were significantly higher (P < 0.05) for all three species when restricted to the top canopy compared to the bottom canopy of plants. These results suggest that within-plant distribution of canola aphids affects aphid reproductive potential, observed as faster population growth on the upper canopy of plants, which may have implications for sampling and management strategies