Population Ecology Group, Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada.
J Insect Physiol. 2011 Sep;57(9):1317-22. doi: 10.1016/j.jinsphys.2011.06.007. Epub 2011 Jun 25.
Phloem-sap feeders (Hemiptera) occasionally consume the dilute sap of xylem, a behaviour that has previously been associated with replenishing water balance following dehydration. However, a recent study reported that non-dehydrated aphids ingested xylem sap. Here, we tested the hypothesis that the consumption of xylem sap, which has a low osmolality, is a general response to osmotic stresses other than dehydration. Alate aphids were subjected to different treatments and subsequently transferred onto a plant, where electrical penetration graph (EPG) was used to estimate durations of passive phloem sap consumption and active sucking of xylem sap. The proportion of time aphids fed on xylem sap (i.e., time spent feeding on xylem sap/total time spent feeding on phloem plus xylem sap) was used as a proxy of the solute concentration of the uptake. The proportion of time alate aphids fed on xylem sap increased: (1) with the time spent imbibing an artificial diet containing a solution of sucrose, which is highly concentrated in phloem sap and is mainly responsible for the high osmotic potential of phloem sap; (2) with the osmotic potential of the artificial diet, when osmotic potential excess was not related to sucrose concentration; and (3) when aphids were deprived of primary symbionts, a condition previously shown to lead to a higher haemolymph osmotic potential. All our results converge to support the hypothesis that xylem sap consumption contributes to the regulation of the osmotic potential in phloem-sap feeders.
韧皮部汁液取食者（半翅目）偶尔会消耗木质部的稀释汁液，这种行为以前与脱水后补充水分平衡有关。然而，最近的一项研究报告称，未脱水的蚜虫会摄取木质部汁液。在这里，我们检验了以下假设：消耗低渗透压的木质部汁液是对除脱水以外的渗透胁迫的普遍反应。有翅蚜虫接受不同的处理，然后转移到植物上，通过电穿透图（EPG）来估计被动韧皮部汁液消耗和主动吸吮木质部汁液的持续时间。蚜虫吸吮木质部汁液的时间比例（即，吸吮木质部汁液的时间/吸吮韧皮部汁液和木质部汁液的总时间）被用作吸收溶质浓度的替代物。有翅蚜虫吸吮木质部汁液的时间比例增加：（1）随着吸吮含有高浓度蔗糖溶液的人工饮食的时间增加，蔗糖主要负责韧皮部汁液的高渗透压；（2）随着人工饮食的渗透压增加，当渗透压过剩与蔗糖浓度无关时；（3）当蚜虫被剥夺初级共生体时，这种情况以前被证明会导致血液渗透压升高。我们所有的结果都支持以下假设：即木质部汁液的消耗有助于调节韧皮部汁液取食者的渗透压。
