Infestation of the coccid, Icerya seychellarum (Westw.), on the mangrove Avicennia marina (forsk.) vierh. on Aldabra Atoll, with special reference to tree age.

The level of infestation by the coccid Icerya seychellarum on the mangrove tree Avicennia marina was measured on a stand of ca. 670 trees on Aldabra Atoll in 1978. Trees varied in basal trunk diameter (btd) between 3 and 30 cm. Leaf infestation increased significantly with increasing btd-class and young trees (btd 3.0-4.5 cm) had a mean infestation of 0.3 mg coccids g-1 leaf whilst the heaviest infested trees (btd 13.0-14.5 cm) supported 7.6 mg g-1. Leaf and shoot growth were not correlated with coccid infestation but shoot vigour (leaf to green shoot ratio) declined significantly with increasing btd-class (or age). Leaves of older, heavily infested trees did not differ from those of young uninfested trees in the concentration of soluble or total nitrogen of in four other leaf elements, indicating that nutrient status was not an important factor in infestation. Field observations showed that many of the older trees were subjected to poor drainage which may have increased their susceptibility to attack and also that on the leaves of young trees salt secretion presented an effective barrier to the establishment of coccids. re19800212.