Viruslike particles in insect cells of three types

Abstract

The fine structure of bacteria, detected in the cytoplasm of spermatogonia, spermatocytes, and spermatids of a Lepidoptera species,Philudoria potatoriaL. (Lasiocampidae), was described using transmission electron microscopy of ultrathin sections through testes. The effects of the bacteria on the germ cells were studied in semithin sections using light microscopy and in ultrathin sections using transmission electron microscopy. Larvae of the animal were collected in the field at the same location in two subsequent summers and the picture was very similar in both preparations. We examined a total of five animals and all were infected. The intracytoplasmic bacteria were usually rod-shaped, up to 1.7 μm long, and about 0.5 μm thick. They lay in intracellular cavities of the germ cells and were separated from the host cell by a membrane. The envelope of the bacteria consisted of two thin electron-dense layers interspersed by a transparent zone which represent the plasma membrane and the cell wall, respectively. Thus, the bacteria are most probably gram-negative. When the cells contained a small number of intracytoplasmic bacteria, pachytene spermatocytes and the development and structure of the meiotic spindles appeared regular. A prominent layer of perispindle membranes that is typical of male meiosis in the Lepidoptera (Wolf, 1994) was, however, missing in the infected animals. A low number of bacteria apparently does not interfere with the onset of spermiogenesis and it is possible that the microorganisms are transmitted into the next generation via the male germ line. In contrast, high numbers of intracytoplasmic bacteria result in cell degeneration in late prophase I of meiosis. Under these circumstances, electron-dense bodies formed within the nuclei and the nucleoplasm became transparent. The most prominent event in the cytoplasm was the aggregation of the mitochondria into large clusters. Finally, the nuclear envelope dissolved and the germ cells degenerated. The intracytoplasmic bacteria ofP. potatoriaare interpreted as parasites.