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First published online April 18, 2006
Journal of Experimental Biology 209, 1777-1783 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02170

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The role of visual cues in directed aerial descent of Cephalotes atratus workers (Hymenoptera: Formicidae)

S. P. Yanoviak^1,2,* and R. Dudley^3,4

¹ Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555, USA
² Florida Medical Entomology Laboratory, 200 9^th Street SE, Vero Beach, Florida 32962, USA
³ Department of Integrative Biology, University of California, Berkeley, California 94720, USA
⁴ Smithsonian Tropical Research Institute, Apdo. 2072, Balboa, Republic of Panama

View larger version (155K): [in a new window]   Fig. 1. Experimental configuration of colored sheets used to evaluate preference in falling ants. The sheets were suspended from a more sheltered location (platform 5-B) for experiments. The arrangement shown here corresponds to run #7 (Table 1).

View larger version (17K): [in a new window]   Fig. 2. Diagram of experimental arrangement as viewed from above (top) and potential landing points as viewed laterally and perpendicularly to the array of sheets (bottom). The null frequency of contact with a sheet is a function of distance from the drop point (P) to its landing position (A–E). Relative to the most direct path (i.e. from P to C), the distance from P to A or to E is 5.1% greater, and from P to B or to D is 1.3% greater. Thus, the proportions used to calculate null frequencies for G-tests were: 0.195 (landing points A and E), 0.203 (landing points B and D) and 0.205 (landing point C).

View larger version (29K): [in a new window]   Fig. 3. Reflectance profiles for each of the six colored sheets. Each point represents the mean (±95% C.I.) of five separate measurements.

View larger version (25K): [in a new window]   Fig. 4. Reflectance profiles for the four sheets used to assess the ants' attraction to targets of different brightness. Each point represents the mean (±1 s.d.) of five measurements. Some points and error bars were omitted for clarity.

View larger version (18K): [in a new window]   Fig. 5. Reflectance profiles for tree trunks (squares, N=21) and surrounding vegetation (circles, N=51 plants). Each point represents the average (±95% C.I.) of the median reflectance values obtained from 40–100 measurements per tree trunk, and from 15 leaf measurements per plant.

View larger version (12K): [in a new window]   Fig. 6. Proportion of dropped ants landing on each of the colored sheets. Values are means ± s.e.m.; N=7 trials for dark gray, gray, green and blue, N=21 for white and black and N=14 for all others; 27–38 ants dropped per trial. Bk, black; Dk, dark gray; Gy, gray; Wh, white; Yl, yellow; Rd, red; Bu, blue; Gr, green. Similar letters indicate lack of difference between means.

View larger version (14K): [in a new window]   Fig. 7. Glide index (horizontal distance/vertical distance) for ants landing on each colored sheet presented individually. Bk, black; Dk, dark gray; Gy, gray; Wh, white; Yl, yellow; Rd, red; Bu, blue; Gr, green. Values are means ±95% C.I.; number pairs indicate the number landing on each sheet out of the total number dropped (i.e. the first in each pair is the sample size for the plotted mean).