Does landscape management influence communities of Psyllopsis and natural enemies on ash trees, Fraxinus excelsior L.?

The impact of landscape management was assessed on communities of Psyllopsis and natural enemies on ash trees, ­ Fraxinus excelsior L. over two growing seasons, 2019 and 2020, in the Shorabil park, Iran. Experimental treatments were cultivating of (1) red clover (C), Trifolium pratense L., (2) rosemary (R), Rosmarinus officinalis L., (3) ornamental cabbage (O), Brassica oleracea , and (4) grass (G), as cover plants around ash trees (A). Three psyllids: Psyllopsis repens Loginova, P. securicola Loginova, and P. machinosus Loginova were collected on ash trees. Which, P. repens with a relative abundance of 73.1% - 80.7% was the main Psyllopsis species on trees. A significant ( P ≤ 0.05) reduction in the population of Psyllopsis , the number of leaf-roll galls, and means of bud-cone-like structures per branch were seen in A-C and A-R plots compared with A-O and A-G treatments. The abundance of Psyllopsis predators per branch was higher in A-C plots than in the other three treatments. The greatest values of the Shannon diversity index ( H ΄ = 1.98 in 2019 and 1.94 in 2020) and the Pielou's evenness index ( J' = 0.90 in 2019 and 0.88 in 2020) for Psyllopsis predators were recorded in A-C plots. The highest parasitism rate of Psyllopsis nymphs by Psyllaephagus claripes Trjapitzin, among treatments, was seen in A-C plots, 34.2 % in 2019 and 29.4 % in 2020. These results indicated that cultivating clover around ash trees could be an effective environmentally-friendly practice in managing Psyllopsis infestations and natural enemies’ communities in the parks.