English abstract
Dubas bug, Ommatissus lybicus Bergevin, is an important pest of date palm in Oman. Huge efforts have been made to control this pest mostly through the use of insecticides. This research was done to determine the effect of pesticide pressure (history of insecticide applications) and other factors on density of dubas bug and abundance and species richness of non-target arthropods, and to test for the presence of insecticide residues in the soil. Arthropod and soil samples were collected from 15 widespread date palm orchard sites in five governorates of northern Oman. Arthropods were collected by beating date palm leaves and sweeping the understory vegetation. Soil samples were collected from under the trees, and then arthropods were extracted from these samples by Berlese traps. Above-ground and soil arthropods were sorted to different groups and counted. GC-MS was used for the analysis of pesticide residue in soil samples extractions. Abundance of dubas bug was higher and abundance of natural enemies was lower in sprayed than in unsprayed sites. Soil arthropods abundance was not significantly different between sprayed and unsprayed sites. Furthermore, insecticide residues of seven commonly used insecticides were not detected in the soil from any of the 15 sites. Dubas bug, non-natural enemy Diptera, and leafhoppers were the most
dant arthropods in above-ground samples, whereas mites and collembolans were the most abundant in soil samples. Abundance and species richness of arthropods were generally higher in understory vegetation than on date palms (with dubas bug abundance excluded). There were significant differences in the abundance of dubas bug and in the abundance and species richness of arthropods in different sites. Spraying history did not fully explain differences between sites, and other factors could be more important as determinants explaining and predicting the density and distribution of dubas bug and other arthropods in date palm agro-ecosystems. Overall, this study indicates a stronger effect of pesticide application on above-ground arthropods than on soil arthropods.
