Sustainable weed management and predatory mite (Acari: Phytoseiidae) dynamics in Tunisian citrus orchards

International audienceThe impact of agroecological weed management on predatory mites (Mesostigmata: Phytoseiidae) is more and more studied. Based on surveys carried out in two experimental sites in Tunisian citrus orchards, this study aims: (i) to compare Phytoseiidae communities on citrus trees and weeds, (ii) to determine dispersal between agrosystem compartments and (iii) to assess the impact of weed management on Phytoseiidae communities. Samples were collected on trees and weeds; dispersal between ground cover and trees was surveyed using traps along tree trunks. Euseius stipulatus and, to a lesser extend, Iphiseius degenerans were the main species on citrus trees. Phytoseiidae were observed in weeds, with diversity and densities varying according to plant species. Phytoseiidae species in weeds were globally similar to those observed on trees. Phytoseiidae were trapped along the trunk; however higher dispersal was observed from weeds to trees than from trees to weeds. In one survey, species moving up the trees were not the same as those present on trees. With respect to weed management strategies, it seems that ploughed plots favour Phytoseiidae mite dispersal from weeds to trees with consequent increases in densities on trees. This weeding strategy therefore requires more attention to determine how its schedule can enhance biological control