Visual field size, binocular domain and the ommatidial array of the compound eyes in worker honey bees

Summary

• 1. The limits of the visual fields and the binocular region of the compound eyes of the worker honey bee were determined by observing the ‘pseudopupil’. The visual field data (Table 1) are valid for a defined, reproducible head-position (Fig. 2). This also means that a stereotaxic system for the bee's compound eyes is now available. The relevant angles are defined in Figs. 1, 3, 4, 5.

• 2. The extent of the binocular domain in the horizontal plane which lies 490 μm above the bases of the antennae (Figs. 2A, 5) is 29 °. The dorsal binocular field in the vertical plane which is perpendicular to the longitudinal body-axis extends over 42 °; the corresponding value for the ventral binocular field is 31 ° (Figs. 5, 6).

• 3. The lines of view of the medial peripheral ommatidia of the compound eyes intersect 5.6 mm in front of the head in the horizontal plane. In the vertical plane, we obtained a corresponding value of 2.8 mm dorsally and 4.7 mm ventrally. Each of these points of intersection marks the start of the binocular space in the respective plane (Figs. 5, 6).

• 4. The visual field is almost a complete sphere (Figs. 6, 7). The extent of the caudally-situated dead space is not due to the shape of the thorax and abdomen; rather, the lines of view of the peripheral lateral ommatidia skirt the outlines of the thorax.

• 5. The ‘monocular-binocular-boundary’ in the facetal array of the compound eye was established. This boundary separates the ommatidia whose lines of sight are directed towards the binocular domain from those ommatidia which look solely into the visual field of the respective eye (= monocular visual field). We further determined the lines of sight and the x-, y- and z-coordinate values of certain ommatidia which lie on this monocular-binocular-boundary (Table 1). 31% of all ommatidia of the bee belong to the binocular region (Fig. 8).

• 6. Medial peripheral ommatidia of one eye and corresponding ommatidia on the monocular-binocular-boundary of the other eye, i.e., ommatidia which look at the same point in space, usually are located ondifferent z-rows (Fig. 9, Table 1).

• 7. The ommatidial array of the compound eye was examined. A regular hexagonal lattice occurs at the centre of the eye; irregularities are present in the dorsal and ventral regions. An x-y-z coordinate system can be used to quantitatively describe the position of particular facets in the ommatidial array (Fig. 8).

• 8. Both the number of x-, y- and z-rows as well as the total number of ommatidia vary from animal to animal and — to a lesser extent — between the right and left eyes of any one bee. The average number of ommatidia per eye is 5,432.

• 9. An estimate was made of the visual fields of the 3 ocelli of the bee (Fig. 10).