Ant attendance changes the sugar composition of the honeydew of the drepanosiphid aphid Tuberculatus quercicola

Mutualistic interactions between aphids and ants are mediated by the honeyd ew produced by aphids. Previous work showed that when attended by the ant F ormica yessensis, nymphs of the aphid Tuberculatus quercicola developed int o significantly smaller adults with lower fecundity than when not ant-atten ded. This study tested the hypothesis that this cost of ant attendance aris es through changes in the quality and quantity of honeydew. Ant-attended an d ant-excluded aphid colonies were prepared in the field, and the sugar con centration and sugar composition of the honeydew of ant-attended colonies w ere compared with those of ant-excluded colonies. The frequency and amount of honeydew excretion were also quantified in the two types of colonies. Th e aphids excreted smaller droplets of honeydew more frequently in ant-atten ded colonies than in ant-excluded colonies. There was no significant differ ence in total sugar concentration between the honeydew of ant-attended aphi ds and ant-excluded aphids. However, ant-attended aphids produced honeydew containing a significantly lower proportion of glucose and higher proportio ns of sucrose and trehalose than did ant-excluded aphids. These results sug gest that the enhanced rate of honeydew-excretion behavior under ant attend ance led to changes in the aphid's physiological status. We suggest that th e increase in the proportions of sucrose and trehalose in honeydew leads to a shortage of carbohydrates available for energy metabolism, resulting in lower performance of the aphids under ant attendance.