110 Tiddens and Cloyd: Rose Susceptibility to Japanese Beetle Feeding which leaflets were collected, had not been treated with any pesticides during the previous 4 weeks. The four side leaflets were excised from the petiole, leaving only the terminal leaf- let. Each petiole was approximately 6.3 cm (2.5 in) long, and each terminal leaflet was approximately 5.1 cm (2 in) long and 2.5 cm (1 in) wide. Immediately after preparation, the petiole of each leaflet was placed into a water pick filled with deionized water, which was then placed individually into an evaluation chamber. Five adult Japanese beetles were re- leased into the center of the evaluation chamber. After 24 hr, leaflets were removed and the petiole was excised. Each leaf- let was then pressed between five pages of newspaper, weighted, and allowed to dry for at least 2 weeks. The ex- periment was set up as a randomized complete block design conducted over five consecutive days with two replications per rose genotype conducted each day. There were a total of ten replications per rose genotype, resulting in 50 dried leaf- lets to be evaluated. Multiple-Choice Experiment Rose leaflets for this experiment were prepared as previously described. One prepared leaflet of each of the five rose geno- types was inserted into a floral water pick and placed into one of the holes in the bottom of an evaluation chamber with the leaflets arranged equidistant from each other. Twenty-five adult beetles were released in the center of the evaluation chamber equidistant from each leaflet. After 24 hr, leaflets were removed and handled as described previously. The ex- periment was set up as a randomized complete block design conducted over four consecutive days with 40 replications per rose genotype, yielding 200 dried leaflets for evaluation. Percentage Leaf Damage and Data Analysis Each pressed and dried leaflet from the no-choice and mul- tiple-choice experiments was mounted into a photographic album (Style No. LM-100D, Pioneer Photo Album Inc., Chatsworth, CA) with Fast-Stick on a white 22 × 30 cm (8.0 × 12.0 in) page with two leaflets per page. Each leaflet was assigned an identification number between 1 and 50. Ten observers evaluated each leaflet for both the 2002 and 2003 albums and assigned an estimated feeding damage rating (%) based on missing leaf tissue. The range was 0% to 100%, including all whole numbers in between (i.e., 51% or 73%). The percentage feeding damage rating data were normal- ized by arcsine square-root transformation and subjected to a one-way analysis of variance (ANOVA) (SAS 2001), with rose genotype as the main effect. Significant treatment means were separated using a Tukey test. Nontransformed data are presented. RESULTS No-Choice Experiment For 2002, rose genotype was highly significant for the per- centage of Japanese beetle adult feeding damage (F12.84; ©2006 International Society of Arboriculture df4, 49; P < 0.0001) based on missing leaf tissue; Nearly Wild had the highest percentage damage rating (77.4%), whereas Knock Out had a significantly lower percentage damage rating (15.1%) (Table 1). In contrast to Knock Out, the other two new rose genotypes, Crimson Bouquet and Love and Peace, experienced more than 50% Japanese beetle adult feeding damage (Table 1). The percentage of Japanese beetle adult feeding damage for rose genotype was not significant for the 2003 no-choice experiment (F1.28; df4, 49; P0.29). All five rose genotypes experienced more than 60% Japanese beetle adult feeding (Table 1). Nearly Wild, as in the 2002 experiment, exhibited the highest percentage damage rating (74.5%) com- pared to the other rose genotypes. Multiple-Choice Experiment For 2002, rose genotype was highly significant for the per- centage of Japanese beetle adult feeding damage (F7.98; df 4, 199; P < 0.0001) based on missing leaf tissue, with all three new rose genotypes experiencing a significantly lower percentage of adult Japanese beetle feeding damage (<50% missing leaf tissue) than the two established rose genotypes (Table 2). All three new rose genotypes experi- enced less than 50% adult feeding damage, whereas the es- tablished roses, Cabbage and Nearly Wild, experienced more than 50% adult feeding damage (Table 2). The percentage of Japanese beetle adult feeding damage for rose genotype was not significant for the 2003 multiple- choice experiment (F 1.77; df 4, 199; P 0.13). Cabbage rose exhibited the highest percentage Japanese beetle damage rating (64.4%) (Table 2). All rose genotypes experienced more than 50% adult feeding damage, with the exception of Crimson Bouquet (Table 2). DISCUSSION Japanese beetle adults fed extensively on all five rose geno- types tested in this study. Although there were statistically significant differences among the rose genotypes, the overall Table 1. Mean (±SE) percentage leaf damage, based on missing leaf tissue, by Japanese beetle, Popillia japonica (Newman), adults for each rose genotype in the 2002 and 2003 no-choice experiments with ten replications per rose genotype. Rose genotype Nearly Wild Cabbage n 10 77.4 ± 1.36 a* 10 58.9 ± 11.81 ab Crimson Bouquet 10 60.5 ± 3.17 b Love and Peace 10 50.8 ± 4.42 b Knock Out 10 15.0 ± 5.11 c 2002 (mean ± SE) 2003 (mean ± SE) 74.5 ± 3.29 a* 63.0 ± 9.57 a 61.8 ± 5.36 a 60.6 ± 2.73 a 69.6 ± 2.73 a *Means within a column not followed by a common letter are significantly different (P 0.05) as determined by a Tukey’s mean separation test.
May 2006
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