The Within-tree distribution of the oriental scale insect, aonidiella orientalis (Newstead)on ficus nitida thumb trees

Abstract

Observations were carried out to study the distribution of the oriental scale insect, Aonidiella orientalis (Newstead) on leaves of four Ficus nitida trees, at the Agricultural Experimental Station of the College of Agriculture, King Saud University, Deirab during 1987 -1988. In all Seasons of the year, no significant differences occurred between the mean number of scales on leaves on the south and west sides ofthe trees. The highest mean number of scales on a single leaf(5.9 individuals) was recorded on leaves on the west, and the lowest (4.15) on leaves on the north side. The highest population always occurred on the west side except during winter when leaves on the south had a higher number of scales. Crawlers seemed to prefer settling in a warmer place during cold weather. In spring, leaves had the highest population (7.15 individuals/leaf), followed by leaves in winter (6.38). The lowest number (2.59) was recorded on leaves during summer. This was most probably due to extremely high temperature which increased mortality among crawlers and adult males. Leaves in the bottom portiop of the tree had more scales than did those of the middle or the upper portions. Leaves inside canopy of the tree had more scales than those of the periphery of the canopy. This may be a photic response. The upper surface of leaves was more densely covered with scales than the lower surface. The population of live scales on the upper surface was approximately 10 times that of the lower surface. This distribution may be due to thermotaxis.