SPATIAL-DISTRIBUTION OF SCALE INSECTS - COMPARATIVE-STUDY USING TAYLORS POWER-LAW

Spatial distribution (quantified by Taylor's power law) and population densities of three scale insect species (Homoptera: Coccoidea) were i nvestigated. The olive stale, Parlatoria oleae (Colvee), was studied o n young and old twigs, and on the spurs of apple trees. The Israeli pi ne bast scale, Matsucoccus josephi Bodenheimer et Harpaz, was studied on the stem, branches, and crown of Pinus halepenis Miller. The effect of fruit phenology on the spatial distribution of the citrus mealybug , Planococcus citri (Risso), was studied on grapefruit trees. The high est density of the olive scale was registered in the spurs, whereas th e Israeli pine bast scale was more abundant on the stem. The citrus me alybug was more abundant during October. There was no effect of the ho st section or phenology on the within-species distribution of the thre e scales, supporting previous claims that the species level of aggrega tion is a species constant. The species index of aggregation for the t hree scale insects was 1.3 for the olive scale, 1.9 for the bast scale , and 1.6 for the citrus mealybug. It is suggested that the observed s patial patterns are the result of the intrinsic behavior of the scales (e.g., thigmotaxis and negative phototaxis during crawlers dispersal) , the morphological characteristics of the host-plant tissue, and the differential activity of natural enemies. The relatively low level of aggregation of the olive scale is probably related to the activity of an efficient natural enemy, a factor which is negligible in the other two scale species.