Structure and Behavior of Spermatozoa of the Fire Ant Solenopsis saevissima (Hymenoptera: Formicidae)1

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Abstract
The length of the live spermatozoon of the fire ant Solenopsis saevissima (Fr. Smith), varies from 69µ to 73µ. The tail has a diameter of approximately 0.6µ and presents a double appearance, resolvable with the electron microscope into a great number of separate fibers and threads. The dorsal flagellar axis, comprising 9+1 fiber doublets and 9 further fibers around the periphery, is the locomotor component. The ventral moiety consists of 2 mitochondrial rods, bearing a series of obliquely sloping structures, repeating every 0.03µ. The sagittal plane of the cell proved to be perpendicular to the plane of locomotor flagellation. The relationship between these axes and the orientation of the central pair of axial fibers was elucidated. Locomotor waves are normally propagated rearwards from the neck region. Active specimens progress in saline up to 5.5µ/sec. During forward locomotion, spinning occurs about the long axis, up to 1 rev/2 sec, probably caused by a helical component in the superficially uniplanar flagellar movements. A trend shown by insect spermatozoa has been toward the extension of the mitochondrial nebenkern along the flagellum. This feature is considered in Solenopsis to be related to their more efficient employment in making energy available for flagellar work. Theoretical considerations by J. W. Flower, given in an appendix to the paper, make it clear that consequent changes in cross-sectional shape do not affect materially the fluid-dynamic efficiency of flagellation.

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