338 Martinson et al.: Water Stress and Geographic Origin Influence Borer Infestations in Ash Cerambycidae) was not associated with ash species or water stress (Table 1). Overall, more green ash trees in this experiment were attacked by borers than were Manchurian ash trees, but the frequency of borer infestation did not vary with water stress (Table 1). No borers were found in the four green ash trees used as cage controls, indicating that the screening and insulation were successful in pre- venting borer colonization of experimental trees. Borer Abundance The abundance (number of borers per tree) of EAB differed significantly between green and Manchu- rian ash but was not a function of water stress or the interaction between ash species and water stress (likelihood ratio tests with df = 1 throughout; ash species × water stress interaction: χ2 water stress: χ2 = 0.01, P = 0.93; ash species: χ2 = 0.69, P = 0.41; = 29.71, P < 0.0001; Figure 3A). Evaluating EAB abundance in surviving trees, again only the effect of ash spe- cies was significant (water stress: χ2 ash species: χ2 = 1.85, P = 0.40; = 25.82, P < 0.0001); the interaction term was not evaluated because EAB were not found in surviving, water-restricted Manchurian ash. As with the frequency analysis, the abundance of clearwing borers (Sesiidae) did not depend on the simple or interactive effects of ash species and water stress, for the full data set (interaction: χ2 0.93; water stress: χ2 = 0.13, P = 0.72; Figure 3B) or among surviving trees only (interaction: χ2 χ2 = 1.75, P = 0.19; ash species: χ2 = 0.02, P = 0.89). Roundheaded borers (Cerambycidae) were more abundant in stressed trees, but abundance was not a function of ash species or the interaction between ash species and water stress (interaction: χ2 = 0.38, P = 0.54; water stress: χ2 0.003; ash species: χ2 = 8.91, P = = 0.54, P = 0.46; Figure 3C). Because few roundheaded borers were found in surviving trees (Table 1), the effects of ash species and water stress on roundheaded borer abundance were not evaluated for the set of surviving trees. As with roundheaded borers, the abundance of bark beetles (Curculionidae) was higher in stressed trees but did not differ among ash species or with the interaction between water stress and ash species (interaction: χ2 12.59, P = 0.0004; ash species: χ2 = 0.02, P = 0.89; water stress: χ2 = 0.46, P = 0.50; = Figure 3D). Among surviving trees, only water stress was an important determinant of bark beetle abun- dance (interaction: χ2 χ2 = 6.21, P = 0.013; ash species: χ2 Table 1. Proportion of trees infested by borers with respect to ash species and water stress (data for surviving trees in parentheses). EAB Sesiidae Cerambycidae Curculionidae Nativesw Any borer Number of trees (Surviving) Fullz 0.75 (0.75) 0.19 (0.19) 0.12 (0.12) 0.06 (0.06) 0.31 (0.31) 0.81 (0.81) 16 (16) watering treatments together). x Green ash Half 0.56 (0.56) 0.25 (0.25) 0 (0) 0.06 (0.06) 0.25 (0.25) 0.69 (0.69) 16 (16) Low 0.62 (0.5) 0.19 (0.33) 0.25 (0) 0.19 (0.33) 0.38 (0.33) 0.75 (0.67) 16 (6) Full 0.19 (0.19) 0.31 (0.31) 0.06 (0.06) 0.06 (0.06) 0.31 (0.31) 0.44 (0.44) 16 (16) Manchurian ash Half 0.12 (0.13) 0.12 (0.13) 0.06 (0) 0 (0) 0.19 (0.13) 0.31 (0.27) 16 (15) χ2 Low 0.25 (0) 0.12 (0.17) 0.19 (0) 0.31 (0.17) 0.25 (0.17) 0.44 (0.17) 16 (6) z Data are presented for the original watering treatments for illustrative purposes. See Methods for details on watering treatments. y Test statistics from contingency table analyses compare frequency of borer infestation in stressed (low watering treatment) versus non-stressed trees (full and half Due to low expected probabilities, log likelihood ratio G tests were conducted, with df = 1 for each test. Asterisk (*) denotes significant tests of association (P < 0.05). w Includes Cerambycidae and Sesiidae. Species 18.9* (17.44*) 0 (0) 0 (0.33 x 0 (0.68 x 0.21 (0.22) 10.9* (11.21*) ) ) tests Treatmenty 0.01 (2.03x 0.21 (0.04 x 4.8* x (1.07x ) ) 8.14* x (4.2* x 0.058 (0.0008 x 0.01 (0.32) ) ) ) = 0.02, P = 0.88; water stress: = 0.40, P = 0.53). = 0.01, P = = 0.14, P = 0.71; ash species: χ2 = 0.01, P = 0.92; water stress: ©2014 International Society of Arboriculture
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