Exudation from Aphid Stylets during the Period from Dormancy to Bud break inTilia americana(L.)

Abstract

Aphid stylet exudation during the period from dormancy to bud break was studied in Tilia americana by means of detached branches brought from the woods into conditions of warmth and extended photoperiod. During physiological dormancy little exudation was obtained. Thereafter until mid-March exudation was more variable, but its onset accelerated progressively until mid-March, after which persistent exudation could be obtained from all branches within 2 days. When the buds were removed from one branch at this time, exudation persisted for only 5 days compared with 14 to 21 days for branches with buds. To account for these results it is suggested that a hormonal factor is produced by the buds which results in sieve-tube activation, that the factor is virtually absent during physiological dormancy, and thereafter requires a few weeks to become fully active. Determinations of sugar concentration, level of exudation, and bud dry weight indicated that exudation was most intense before the bud sinks were active and then rapidly falls off. It is suggested that the stylet acts as a sink competing with the natural sinks for solutes from a limited region of the stem. Other interpretations are also considered.