visual field of a cricket (Gryllus campestris) induce an antennal tracking response. It consists of move- ments of the ipsilateral antenna following the target.
Journal of Comparative Physiology. A
J Comp Physiol (1981) 142:419-42I
9 Springer-Verlag 1981
A Preliminary Note on a New Optomotor Response in Crickets: Antennal Tracking of Moving Targets H.-W. Honegger Fakult/it f~r Biologic, Universitfit Konstanz, Postfach 5560, D-7750 Konstanz, Federal Republic of Germany Accepted January 30, 1981
Summary. Black disks moving horizontally in the visual field of a cricket (Gryllus campestris) induce an antennal tracking response. It consists of movements of the ipsilateral antenna following the target in a saccade-like fashion.
Insects follow visual cues in their environment by movements of their whole body, i.e., they display an o p t o m o t o r response; they orient toward stationary objects, or track moving targets (reviews see Land 1977; Wehner 1979). This paper describes a new o p t o m o t o r response to moving visual targets which is performed by adult males and females of the cricket Gryllus campestris. When a black disk is moved horizontally in front of a white background in the frontal and lateral visual field of a cricket, the ipsilateral antenna (with respect to the object) tracks the object, i.e., follows its course while pointing at it in the range 0 ~ (straight ahead) to about 90 ~ lateral from the body's long axis (Fig. 1C, D). When the object crosses the midline in front of the animal (0 ~ tracking is taken over by the other antenna (Fig. 2A). Only in rare cases does the contralateral antenna also follow an object as far as 30 ~ lateral (Fig. 1B). When an object appears in the lateral or frontal visual field, one or both antennae fix this object immediately but soon 'lose interest' when the object does not continue to move. When crickets track moving targets with their antennae they remain motionless for as long as 15-20 s. As soon as an animal starts to move, its antennae no longer track the target. During tracking of a moving target the instantaneous antennal positions can be measured with respect to the target positions. Figure 2A shows two antennal tracking responses to a uniformly moving
black disk with a visual angle of 26 ~ The antennal movements appear to be saccadic but further analysis will be required to verify this. When 31 tracking responses of 17 different individuals were averaged, it could be shown clearly that the antennae tended to fix the leading edge of the target during movements from 0 ~ toward lateral right and left. During the backward movements of the target, the antennae tracked the trailing edge (Fig. 2B). At target positions beyond 60 ~ lateral the average antennal positions were smaller than the instantaneous positions occupied by the leading or trailing edge of the target. This type of response could be induced with disks of sizes between 13-48 ~ visual angle and at angular rates of movements from 18-225~ (tested with a disk size of 33~ Antennal movements in the horizontal plane are governed by the joint between scapus and pedicellus and movements in the vertical plane by the joint between head capsule and scapus. Saccadic-like tracking movements are made with both joints. At 90 ~ lateral, when the scapus is extended in a horizontal plane, the shaft of the pedicellus locks against the upper rim of the scapus. Movements further backward require a lift of the pedicellus. This movement seems to be inhibited and this could be the reason why most crickets did not move their antennae farther laterally than 80-85 ~ (Fig. 2A, B). Only occasionally a cricket moved its antennae beyond 110 ~ lateral with short flicks. It is suggested that mechanoreceptors in the antennae monitor this antennal catch. Antennal tracking appears to be an attempt to investigate approaching or passing objects with the mechano- and chemoreceptors on an appendix which extends farthest away from the animal. Thus, an object can be already investigated before it comes too close. The tracking response of the antennae could be b a s e d on visual control of the antennal position or a position control in the muscles which move the
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Fig. 1 A - D . Antennal tracking of Gryllus campestris in response to a black disk moving around the frontal part of the cricket in the horizontal plane. Different instantaneous positions are shown. A Target in 0 ~ position in front of the animal. C Target position lateral left; D target position lateral right; B rare response where one antenna follows the target beyond the midline to the contralateral side. Crickets were fixed at the pronotum and suspended over a floating styrofoam ball on which they could walk
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H.-W. Honegger: Antennal Tracking in Crickets
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Fig. 2A, B. Comparison between horizontal movement of a disk with 26 ~ visual angle (hatched zone) and antenna1 movements. Targetand antennal movements were recorded with a video system. Antennal positions were measured for all target positions in 10~ steps by single picture analyses. Measurements were made starting at target position in front of the cricket (0 ~ cf. Fig. 1A) to 100~ lateral right (cf. Fig. 1D) and then through a half circle around the cricket to 100 ~ left (cf. Fig. 1C) and back to 0 ~ x-axis: Deviation from 0 ~ to the right (R) and left (L). y-axis: movement of target and antennae to right (R) and left (L). A Two antennal tracking responses of one cricket. Note the saccadic structure of the antennal movements. B Means of 31 tracking responses of 17 crickets. Vertical lines: standard deviations
antennae and/or antennal joints. Experiments to unvail these questions are in progress.
This work was supported by a grant from the Deutsche Forschungsgemeinschaft Ho 463/12.
References Land M F (1977) Visually guided movements in invertebrates. In: Stent GS (ed) Function and formation of neural systems. Dahlem Konferenzen, Berlin, pp 161-177 Wehner R (1979) Pattern recognition in insects: Localisation and identification of visual objects. Verh Dtsch Zool Ges 19~4 1
