Pathological changes in the cortex of Pinus halepensis (Coniferales: Pinaceae) as related to injury by Matsucoccus josephi (Insecta: Homoptera: Margarodidae)

Abstract

Stems of Pinus halepensis Mill. infested by Matsucoccus josephi Bodenh. and Harpaz were examined for injury caused by the larval stage of the pest. The earliest detectable pathological changes occur in the cortical parenchyma of 3-month-old stems. Presence of one to two larvae results in flag-shaped banding of young growth due to lysis of the outer parenchyma layers. Infestation with four or more larvae per 1-cm stem segment results in its death a few weeks after the emergence of the adults. Early visible histological changes, i.e., hypertrophy of parenchyma cells, are observed in stems 10–15 months of age. High density of female scales per branchlet results in hypertrophy, high polyphenol content, lysis of the parenchyma cells, numerous radial phloem ducts, and the collapse of the cortex layers. Cortex deterioration occurs from several days to several weeks after emergence of the adult females. Wound periderm that is initiated following scale injury in infested mature stems produces an early rhytidome resulting in a cork layer that separates the nonfunctioning injured cortical cells from the living tissue. This process ends in early cracking of the outer bark, peeling of flakes, and exposure of the outer distal end of resin ducts, thus resulting in excretion of resin droplets on the bark.