EFFECTS OF BALSAM WOOLLY APHID (ADELGES PICEAE) INFESTATION ON CAMBIAL ACTIVITY IN ABIES GRANDIS

Salivary secretions injected into the cortex or outer phloem by Adelges piceae (balsam woolly aphid) feeding on Abies grandis induce the production of wood that is in some respects similar to compression wood. Cambial activity was analyzed by examination of serial tangential sections through an annual ring in the xylem produced before infestation occurred and compared with similar sections from a ring produced after infestation. Growth after infestation was characterized by increased periclinal and anticlinal divisions of fusiform initials, increased production of new ray initials from fusiform initials and from anticlinal divisions of existing ray initials, and decline of numerous fusiform initials and termination of many tiers by maturation. This results in increased frequency of ray fusion and separation by decline or intrusion of adjacent fusiform initials. There was a marked increase in size and number of rays and number of parenchyma strands both of which also distinguish aphid-affected wood from compression wood with which it frequently has been compared.