Feeding location affects demographic performance of cabbage aphids on winter canola

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae), is a perennial pest that specializes on plants of the Brassicaceae family, attacking winter canola (Brassica napus L.) mainly during and after flowering. Under field conditions, cabbage aphid colonizes the upper flowering canopy. Population dynamics of aphids in the flowering canopy could be regulated by differences in either plant quality (bottom-up) or predatory (top-down) forces. The goal of our study was to determine the effect of feeding location on cabbage aphid demography. A stage-structured matrix population model was constructed for aphids restricted to reproductive or vegetative plant tissues of canola. We found that feeding location had a large impact on demography of cabbage aphid; the finite rate of increase (k SEM) was higher when aphids were restricted to reproductive tissues, compared to aphids feeding on vegetative tissues: 1.25 0.01 vs. 1.17 0.01 (leaves). Aphids confined to reproductive tissues with higher k exhibited shorter generation times (T = 14.2 0.2 days) and 53–75% higher net reproductive rates (R0 = 23.3 1.7) than aphids feeding on vegetative tissues. Prospective analyses showed that there was a nymph-skewed stable stage distribution, and elasticity values revealed that k is most sensitive to changes in stasis of adults staying in the adult stage and to adult survival. Retrospective analyses indicated that variation in adult fecundity (value of 0.05) had the largest effect on population dynamics but collectively, growth of nymphal stage 2–3, 3–4, and 4 to adult accounted for most of the difference in k between the treatments. Monitoring programs should target adults and penultimate instars colonizing reproductive tissues of canola plants in the field as aphids on these plant structures contribute most to population growth.