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Visual control of host pursuit in the parasitoid fly Exorista japonica

Yoshifumi Yamawaki^1,*, Yooichi Kainoh² and Hiroshi Honda²

¹ Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812-8581, Japan and
² Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan

View larger version (14K): [in a new window]   Fig. 1. (A) Diagram of the fly and host defining the variables used for the analysis. The angle of the fly’s longitudinal axis () is measured relative to externally based coordinates. The angular position of the host head (H) and tail (T) are measured relative to . (B) Diagram of the fly in two frames to illustrate the fly’s movement, consisting of rotation () and translation. Translation is resolved into two components, forward (F) and sideways (S).

View larger version (22K): [in a new window]   Fig. 2. Frames from a video sequence of a fly pursuing the host larva. Times after first frame are shown for each frame (A–D).

View larger version (16K): [in a new window]   Fig. 3. (A) An example of ‘approach’ pursuit by the fly. The open circles and short lines represent the fly’s head and body axis, respectively, when the fly had paused. The filled circles and long lines represent the host’s head and body axis, respectively, when the fly is at the corresponding numbered position. (B) Absolute angles of the fly’s axis () and the positions of the host’s head (+H) and tail (+T) during the pursuit shown in A. Numbered points correspond with those in A.

View larger version (20K): [in a new window]   Fig. 4. An example of pursuit after approach (A). Conventions are as in Fig. 3. Forward (B) and sideways (C) distances travelled by the fly between successive frames. (D) Changes in the angle of the fly’s axis over time. Data are plotted only for the first 2 s of the pursuit shown in A (9 s). Open circles in B–D represent frames when the fly had stopped.

View larger version (9K): [in a new window]   Fig. 5. Run (N=1560) and stop (N=1560) durations during pursuit. Horizontal bars indicate the 10th, 25th, 50th (median), 75th and 90th percentiles of the duration.

View larger version (23K): [in a new window]   Fig. 6. Scatterplot showing the duration of the stop interval as a function of the angular velocity of the host’s head (A, H) and tail (B, T) during a stop period in the approach of a fly to the host. The insets indicate the mean stop duration + S.D. of each bin (bin width 10° s–1) when the angular velocity of host’s head or tail is less than 80° s–1.

View larger version (29K): [in a new window]   Fig. 7. Total amount of translation (A) and rotation (B) during a run as a function of the duration of the run.

View larger version (30K): [in a new window]   Fig. 8. (A) Scatterplot showing the total amount of forward translation as a function of sideways translation during a run. (B) Histogram of the direction of translation with respect to the forward direction.

View larger version (18K): [in a new window]   Fig. 9. (A) Correlation coefficient between the total amount of rotation during a run and the angular position of the host’s head, tail and centre. The angular position of the host’s centre is the average of those of the head and tail. The host’s angular position from five frames before to three frames after the start of the rotation was used for analysis. (B) Total amount of rotation during a run as a function of the angular position of the host’s head 33 ms (one frame) before the start of the rotation.

View larger version (18K): [in a new window]   Fig. 10. Total amount of rotation as a function of the angular position of the host’s head when the host’s head was moving towards the midline of the fly (A) or away from it (B).

View larger version (28K): [in a new window]   Fig. 11. Total amount of forward (A) and sideways (B) translation during a run as a function of the angular position of the host’s head 33 ms (one frame) before the start of the run.

View larger version (28K): [in a new window]   Fig. 12. Direction of translation during a run as a function of the angular position of the host’s head.

View larger version (35K): [in a new window]   Fig. 13. Total amount of forward (A) and sideways (B) translation during a run as a function of the visual angle subtended by the host.