[Probability distribution of Orthezia praelonga Douglas (Hemiptera: Sternorrhyncha: Ortheziidae) in citrus]

The probability distribution of the orthezia scale, Orthezia praelonga Douglas, was studied in plots of commercial orange orchards (Citrus sinensis L., var. "Pêra Rio"), with 5, 9 and 15 years of age, during one year. The survey of presence or absence of the pest in the plants was carried through twenty samplings in the total area of each plot visually inspecting each plant. The dispersion indexes used were: variance/mean relationship (I), index of Morisita (Id), coefficient of Green (Cx) and k exponent of negative binomial distribution for each sampling. The negative binomial distribution was more representative of the frequency distribution data of this scale in citrus, since the variance was superior to the average in all samplings. The analysis of the aggregation index showed that the majority of the samplings presented aggregate distribution for the scales.