DIVERSITY AND ABUNDANCE OF PHYTOSEIIDAE (ACARI: MESOSTIGMATA) IN THREE CROP MANAGEMENT STRATEGIES OF CITRUS ORCHARDS IN TUNISIA

Surveys of Phytoseiidae were carried out in three Tunisian citrus orchards; the first was conducted according to organic farming practices; the second was conducted according to integrated pest management; the third was conventionally conducted with an intensive use of pesticides. The aim of the present study was to assess Phytoseiidae diversity and densities in these orchards both on trees and weeds. The highest Phytoseiidae diversity on citrus and weeds was observed in the organic citrus orchard (eight species on citrus and eight species on weeds). In the conventionally managed orchard, only three and four species of Phytoseiidae were found on weeds and trees, respectively. The same species, Euseius stipulatus, was dominant on citrus in the three orchards, whereas it was observed only on some weeds. The prevalent Phytoseiidae species were different according to the orchards (Typhlodromus [Typhlodromus] phialatus in organic farmed plot, Neoseiulus californicus in integrated managed plot and Phytoseiulus persimilis in the conventional one). Prevalence of such species was due to their high abundance on some plants (i.e. Phaseolus vulgaris for P. persimilis). No clear impact of weed management on citrus Phytoseiidae fauna was observed. However, pesticide use seems to affect densities and diversity of Phytoseiidae. Even if no clear correlation between E. stipulatus and Tetranychus sp. was observed, it seems that E. stipulatus could feed on Tetranychus sp. but cannot quickly and efficiently control high densities of these pests.