The interrelationships of 2 diaspidid scale insects of the geunus Parlatoria, infesting citrus, were investigated during several years in the field. It was found that P. pergandii Comstock was more numerous in the summer, P. cinerea Hadden in the winter. With reference to the respective geographical distribution of these species, it is postulated that climatic conditions annually modify the common habitat and thus determine the outcome.