Diapause and its regulation in the whitefly Trialeurodes lauri.

This study focuses on the regulation of synchronization between the life cycle of the oligophagous whitefly, Trialeurodes lauri (Signoret), and its evergreen host tree Arbutus andrachne in Mediterranean chaparral. Whitefly infestations vary considerably among trees. The adults of the univoltine (one generation per year) whitefly emerge en masse during April and May and oviposit on the new spring foliage. Following approximately one month of development to the early fourth instar, the nymphs enter nine-month diapauses, terminating in February. This diapause is induced and maintained by the plant and can be experimentally avoided (in the case of developing young nymphs) or terminated (in the case of diapausing fourth instars), if whitefly-bearing branches are severed from the tree and placed in water under laboratory conditions. This study is the first report of a whitefly diapausing through both summer and winter seasons. The role of the host plant in the process is discussed.

Adsorption, capping, and release of a complex bacteriophage by mycoplasma cells.

By electron microscopic studies, the adsorption and release of nonlytic, cytocidal mycoplasma virus MVL3, which infects ACholeplasma laidlawii cells, have been examined. The MVL3 virion has a polyhedral head, collar, short tail, and tail fibers and contains linear double-stranded DNA. Adsorbed MVL3 virus showed a temperature-dependent clustering or capping on the mycoplasma cell membrane. During infection, a number of virus-cell membrane-related structures were observed, suggesting a general model in which MVL3-infected cells release progeny virions in membrane vesicles. These vesicles must then break down to release MVL3 particles.

Inhibition of mycoplasma cell division by cytochalasin B.

Mycoplasma gallisepticum has subcellular organelles which may function as a primitive "mitotic-like" apparatus. To investigate these further, we have studied the effects of cytochalasin B (CB) on M. gallisepticum. We found that CB inhibits cell division; this is the only procaryote thus far reported to be inhibited by CB. CB does not inhibit glucose or macromolecule precursor uptake. It stops cellular DNA synthesis, however, although RNA and protein synthesis continue (at a reduced rate). CB removal results in a resumption of DNA synthesis, followed by cell division. There appears to be some degree of cell synchrony in this first division after CB removal. These results, together with morphological data, indicate that CB blocks at two points in the cell cycle: at the time "mitotic-like" structures are formed and at the time of cell division. It is suggested that the CB blocks may result from a disruption of actin-like protein structures required at these points in the cell cycle.