Effect of Balsam Woolly Aphid,Adelges piceae(Ratz.), Infestation on the Xylem ofAbies grandis(Doug.) Lindl.

Abstract

Studies of the sapwood of aphid-attacked Abies grandis (Doug.) Lindl. showed that the infestation by Adelges piceae (Ratz.) did not cause ‘rotholz’, the abnormal xylem usually produced in response to aphid attack. The tracheid length, annual ring width, and per cent latewood per annual ring were not significantly different between the wood of infested and non-infested trees. Gas permeability, in combination with a modified Adzumi equation, was used to determine the total number and size of the conducting pit-membrane pores and tracheid lumina. In infested and non-infested sapwood dried by solvent exchange, the average pore radius of the pit membrane was calculated to be about 0.l μm. The radius of the pit pore, and the tracheid lumina and the number of conducting tracheid lumina were not significantly different in the infested and non-infested wood. Infestation reduced the number of pit pores per conducting tracheid in the wood by a factor of about three. The reduced number of conducting pit pores may have lowered the permeability of the infested wood by directly reducing the number of available flow channels.