Vertical position of traps influences captures of eastern cherry fruit fly (Diptera: Tephritidae).

The eastern cherry fruit fly, Rhagoletis cingulata (Loew), is an important late-season pest of cherries in the eastern and Midwestern United States (Bush 1966). Adults emerge from overwintering puparia in mid-June, mate on the host fruit, and lay eggs into cherries (Pettit & Tolles 1930; Boller & Prokopy 1976; Smith 1984). Michigan produces approximately 75% of the total U.S. tart cherries, Prunus cerasus L., and 12% of the U.S. sweet cherries, P avium (L.) L. (Anon. 2004). Zero tolerance standards for fly larvae in fruit require sensitive fly monitoring systems early in the growing season as part of integrated pest management (IPM) programs to prevent fruit infestation. To monitor R. cingulata flies, Pherocon AM boards are placed approximately 2.1 m (depending on the tree size) from the ground within the tree canopy. The yellow traps are typically baited with an ammonia and protein hydrolysate lure (Liburd et al. 2001), providing both visual and olfactory cues to attract flies. The first insecticide is applied after a single fly is captured on a monitoring trap. Steady progress has been made in developing effective trapping systems for some important Rhagoletis pests of temperate fruit crops. Trap placement has been optimized for monitoring the apple maggot fly, R. pomonella (Walsh), (Reissig 1975; Drummond et al. 1984) and the blueberry maggot, R. mendax Curran (Liburd et al. 2000; Teixeira & Polavarapu 2001). The optimal position for traps to monitor R. pomonella is approximately 2.1 m above the ground (depending on the tree size) within the apple tree canopy (Reissig 1975; Drummond et al. 1984) and 0.25-0.5 m from fruit, while traps for R. mendax are most effective when placed within the top of highbush blueberry plants, Vaccinium corymbosum L., when the bushes are 1.5 to 2.0 m high (Liburd et al. 2000; Teixeira & Polavarapu 2001). To date, the optimal positioning of traps for monitoring R. cingulata has not been reported; however, based on studies of related fruit fly species, we hypothesized that the height of trap placement within the cherry tree canopy would affect captures of R. cingulata on monitoring traps. In 2002 and 2003, trap heights were compared in mature, unmanaged tart cherry orchards located in southwestern Michigan (Van Buren Co.) with high populations of R. cingulata. The orchards used in these experiments contained unsprayed, mature trees approximately 4.6 m in height, and planted in a 2.4-m within-row by 6.1m between-row spacing. This spacing allowed sunlight to reach the entire tree, rather than the topmost portion only. In addition, branches from adjacent trees did not overlap. The effect of trap height on captures of R. cingulata was determined by placing unbaited Pherocon AM traps (Trece, Inc., Adair, OK) at three positions midway between the tree trunk and outermost foliage of cherry trees. All traps were placed on the southwest side of trees. Three treatments were evaluated that included placing traps as follows: (1) below the tree canopy (approximately 1.2 m above ground), (2) at the standard trap height (approximately 2.1 m), or (3) in the top portion of the tree canopy (approximately 4.6 m). In order to obtain the highest trap position, traps hung at 4.6 m were suspended from a PVC pipe (1.4 m length and 6 mm diam.) affixed to a tree limb such that the traps were within the top portion of the cherry tree foliage midway between the trunk and the outermost foliage. Trees were selected randomly and a single trap was placed at one of the three positions in each tree. Treatments were arranged with a distance of at least 20 m between trees and 30 m between blocks. Foliage surrounding all traps was removed in a 0.5 m radius (Reissig 1975). Five replicates of each treatment were arranged in a randomized complete block design. Flies were counted and removed from traps weekly for six weeks in both years (17 June-30 July 2002 and 16 June-29 July 2003). To minimize position effects, all treatments were rotated one position clockwise after each weekly inspection. Total fly captures on each trap across the season in both years were subjected to analysis of variance (ANOVA). To normalize the data, square root-transformation (x + 0.5)1/2 was performed prior to analysis. Fisher's Least Significant Difference test (LSD, SAS Institute 2000) was used to separate mean differences among treatments (significance level ox = 0.05). In 2002, captures of R. cingulata were significantly affected by trap location (F = 79.2; df= 2,8; P < 0.05), with more R. cingulata flies caught at 4.6 m within canopies of cherry trees than on traps placed at 2.1 m (standard trap height) or 1.2 m (Fig. 1A). Overall, more than three times the number of flies were captured on traps placed at 4.6 m compared with traps hung at lower positions. In 2003, captures of R. cingulata flies were significantly affected by trap location (F = 27.0; df = 2,8; P < 0.05). Significantly more flies were caught on traps hung at 4.6 m compared with traps placed at a 2.1 m or 1.2 m height (Fig. 1B).