Histological studies of Pinus halepensis stem xylem affected by Matsucoccus josephi (Homoptera: Margarodidae)

The injury caused by Matsucoccus josephi Bodenheimer & Harpaz to naturally and artificially infested Pinus halepensis Mill. was studied with special emphasis on the reaction of the cambium to the insect attack and the subsequent changes in the xylem. Scars from stem injury were easily detected macroscopically due to discoloration on the stem cross section and involve narrowing of annual rings at the injury site for several years. Microscopic sections reveal production of abnormal xylem in the injured zone, i.e., lignified parenchyma cells instead of tracheids, curved tracheids and lignified resin ducts. Histological disorganisation is compared with mechanical injuries. Changes in the orientation of cells in the xylem suggest that the effect of infestation is not only mechanical; interrupted polar auxin transport into loops is probably responsible for abnormal xylem formation.