Psyllopsis species, their densities, and gall formation
In this study, P. repens, P. securicola, and P. machinosus were collected on the branches of ash trees. P. repens, with a relative abundance of 73.1% in 2019 and 80.7% in 2020, was the main Psyllopsis species on the branches of ash trees in two growing seasons (F3, 9 = 109.26; P ≤ 0.001 in 2019; F3, 9 = 137.08; P ≤ 0.001 in 2020) (Fig. 1). P. securicola and P. machinosus occurred at low abundances on the branches of ash trees over the growing seasons of 2019 and 2020 (Fig. 1).
The cultivation of four ornamental plant around ash trees significantly influenced the populations of Psyllopsis eggs (F3, 9 = 58.59; P ≤ 0.001 in 2019; F3, 9 = 44.29; P ≤ 0.001 in 2020) and nymphs (F3, 9 = 35.62; P ≤ 0.001 in 2019; F3, 9 29.37; P ≤ 0.001 in 2020) on ash branches. The lowest densities of Psyllopsis eggs and nymphs per branch were seen on A-C plots. In addition, A-R treatment statistically decreased Psyllopsis eggs and nymphs compared with A-O and A-G plots (Table 1). Similarly, the least number of leaf-roll galls (F3, 9 = 14.03; P ≤ 0.001 in 2019 and F3, 9 = 13.74; P = 0.001 in 2020) and bud-cone-like structures (F3, 9 = 11.92; P = 0.002 in 2019 and F3, 9 = 9.88; P = 0.003 in 2020) per branch were recorded in A-C plots. Furthermore, a significant decrease in the number of leaf-roll galls and bud-cone-like structures per branch was observed in A-R treatment than in A-O and A-G (Fig. 2 and 3).
Natural enemies
In this study, nine species of Psyllopsis predators were collected on the infested ash trees during two growing seasons (Table 2). Among them, Anthocoris nemoralis (Fabricius) and Temnostethus reduvinus parilis (Horváth) (Hemiptera: Anthocoridae), as well as Chilocorus bipustulatus (L.) (Coleoptera: Coccinellidae) were the main predators of Psyllopsis on ash trees in two seasons (Table 2). Afterward, Orius niger (Wolff) (Hemiptera: Anthocoridae), Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae), Episyrphus balteatus (De Geer) (Diptera: Syrphidae), Anthocoris nemorum (L.) (Hemiptera: Anthocoridae), Deraeocoris punctulatus (L.) (Heteroptera, Miridae), and Anystis baccarum (L.) (Acari: Anystidae), respectively occurred at low abundances (Table 2). The discrepancy in A. nemoralis abundance was greater in A-C treatment compared with A-R, A-O, and A-G in 2019 (F3, 9 = 38.25; P ≤ 0.001) and 2020 (F3, 9 = 42.19; P ≤ 0.001). The least abundance of A. nemoralis occurred in A-R plots in 2020 (Table 2). The density of C. bipustulatus was statistically enhanced in A-C than in A-R and A-G in 2019 (F3, 9 = 16.31; P ≤ 0.001) and 2020 (F3, 9 = 19.06; P ≤ 0.001; Table 2). The populations of T. reduvinus parilis were strongly enhanced in A-C than in other treatments in 2019 (F3, 9 = 24.30; P ≤ 0.001) and 2020 (F3, 9 = 19.73; P ≤ 0.001; Table 2). Moreover, the least abundance of T. reduvinus parilis was recorded in A-R in two years (Table 2). The densities of other predators of Psyllopsis including O. niger, C. carnea, E. balteatus, A. nemorum, D. punctulatus, and A. baccarum on ash branches were amended in A-C plots compared with the other three treatments in two seasons (Table 2). In general, the greatest total abundance of Psyllopsis predators was documented in A-C plots. Besides, the discrepancy in total abundance of Psyllopsis predators was greater in A-O and A-G compared with A-R in 2019 (F3, 9 = 114.71; P ≤ 0.001) and 2020 (F3, 9 = 136.84; P ≤ 0.001) (Table 2). The maximum values of the Shannon diversity index (F3, 9 = 8.63; P = 0.005 in 2019 and F3, 9 = 9.34; P = 0.004 in 2020) and the Pielou’s evenness index (F3, 9 = 6.71; P = 0.011 in 2019 and F3, 9 = 7.01; P = 0.010 in 2020) for the complex of Psyllopsis predators were statistically calculated in A-C plots over the whole growing season (Table 2). Moreover, the values of the Shannon diversity index and the Pielou’s evenness index were higher in A-O and A-G contrasted with A-R in both years (Table 2).
In the present research, only one parasitoid species Psyllaephagus claripes Trjapitzin emerged from the parasitized nymphs of Psyllopsis across all treatments. In two years, the average parasitism rate of Psyllopsis nymphs per branch was statistically greater in A-C plots than other three treatments (F3, 9 = 13.64; P = 0.001 in 2019 and F3, 9 = 17.19; P ≤ 0.001 in 2020; Fig. 4). Furthermore, the parasitism rate of Psyllopsis nymphs was higher in A-O and A-G plots compared with A-R in two seasons (Fig. 4).
Plant growth
Ash trees showed longer new branches in A-C plots contrasted with A-R, A-O, and A-G treatments (F3, 9 = 37.42; P ≤ 0.001 in 2019 and F3, 9 = 23.86; P ≤ 0.001 in 2020; Table 3). Similar results were recorded in the number of leaves per branch among the four treatments in 2019 (F3, 9 = 19.57; P ≤ 0.001) and 2020 (F3, 9 = 31.08; P ≤ 0.001) (Table 3). In this study, the difference in the dry weight of leaves was not significant among the four treatments in 2019 (F3, 9 = 3.14; P = 0.080) and 2020 (F3, 9 = 2.61; P = 0.116) (Table 3).