Aphid-induced reduction of shoot and root growth in Douglas-fir seedlings

1. The short- and long-term effects of photosynthate removal by sap-sucking herbivores on plant growth were examined by experimentally manipulating densities of an aphid Cinara pseudotsugae (Wilson) on 2-year-old Douglas-fir seedlings Pseudotsuga menziesii (Mirb.) Franco under greenhouse conditions. An 18-week test was conducted to determine short-term effects. Effects of long-term aphid feeding were examined by exposing seedlings to aphid feeding for two consecutive growing seasons. A third experiment evaluated the extent of recovery during 1 year following a single season of aphid feeding. At least 35 seedlings were used in each test. 2. Volume and dry weight of both shoots and roots decreased significantly with increasing aphid feeding in all three experiments. 3. The most significant and severe aphid effect was reduced root tissue density, suggesting carbohydrate depletion due to translocation from roots to shoots. 4. There was no sign of recovery, of either root or shoot growth, during the year following one season of feeding. 5. The results of this study indicate that short-term feeding by aphids can affect plant growth and structure for a relatively long time.