Spatial distribution of scale insects: comparative study using Taylor's power law.
Spatial distribution (quantified by Taylor's power law) and population densities of 3 scale insect species were investigated in Israel. Parlatoria oleae was studied on young and old twigs and on the spurs of apples trees. Matsucoccus josephi was studied on the stem, branches, and crown of Pinus halepensis. The effect of fruit phenology on the spatial distribution of Planococcus citri was studied on grapefruit trees. The highest density of Parlatoria oleae was registered in the spurs, whereas M. josephi was more abundant on the stem. Planococcus citri was more abundant during October. There was no effect of the host section or phenology on the within-species distribution of the 3 pests, supporting previous claims that the species level of aggregation is a species constant. The species index of aggregation for the 3 scale insects was 1.3 for Parlatoria oleae, 1.9 for M. josephi and 1.6 for Planococcus citri. It is suggested that the observed spatial patterns are the result of the intrinsic behaviour 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 Parlatoria oleae is probably related to the activity of an efficient natural enemy, a factor which is negligible in the other 2 scale species.