Seasonal variation in honeydew sugar content of galling aphids (Aphidoidea: Pemphigidae: Fordinae) feeding on Pistacia: Host ecology and aphid physiology

We investigated the possibility that seasonal variation in host-tree sap quality was reflected in aphid honeydew sugar content. Aphids (Homoptera) feed on the phloem sap of their host plants and excrete sugar-rich honeydew. We compared the sugar composition of honeydew excreted by four species of closely related aphids (Pemphigidae: Fordinae ) inducing galls on Pistacia palaestina (Anacardiaceae). Samples were collected four times a year in 1997 and 1998. Samples from one species feeding on the roots of a secondary host, a perennial herb, were also included in the study. More than 20 sugars were detected in the honeydew. Sugars that were present in more than 40% of the samples were analyzed quantitatively in a hierarchical manner. The mean proportions of each sugar of the total sugar content in different species were not significantly different, but samples taken at different dates contained significantly different proportions of the sugars. The most frequent sugars in all species were glucose and fructose. Generally, the proportion of glucose exceeded fructose, but in honeydew from aphids feeding on the roots of the secondary host the reverse was true. We suggest possible explanations for the observed patterns, and discuss a possible contribution of Fordinae honeydew to the food web in the micro-ecosystem.