SPATIAL PATTERN OF SAISSETIA-OLEAE (HOMOPTERA, COCCIDAE) IN GREECE

The spatial pattern and the spatial density dependence of mortality of Saissetia oleae (Olivier) were studied under field conditions. The re sults indicated that the distribution of S. oleae was highly aggregate d and the degree of aggregation changed considerably during tile gener ation, as indicated by the values of the exponent k of negative binomi al distribution and the I-delta index of aggregation. Aggregation incr eased during the ovipositional period in summer and during winter, whe reas it decreased during autumn and spring. The increased aggregation during summer was caused by the combined effect of crawler behavior as they searched for settlement, and of mortality, which is negatively r elated to population density. During autumn, and possibly during sprin g when the main action of natural enemies occurred, the reduced aggreg ation was caused by the direct density dependence of mortality. This r elationship was determined to a certain extent by the action of the in ternal parasitoid Metaphycus helvolus (Compere). The increased aggrega tion during winter was attributed to an inverse density-dependent rela tionship between mortality and population density and also to larval m ovement from leaves to branches. A strong relationship between the mea n and variance of population density (Taylor power law) was establishe d with 2 types of sampling units (leaf, branch). The corresponding 2 v alues of the coefficient b were remarkably similar. However, the expon ent k of negative binomial and the Morisita index of aggregation (I-de lta) were found best to describe changes in the spatial pattern during the generation compared with the Taylor relationship.