Viruslike particles in cells associated with sensilla in head appendages of a dytiscid beetle

Two types of viruslike particles (VLP) were noted in the cytoplasm of cells associated with sensilla on the antennae and labial palps of the diving beetle Graphoderus occidentalis Horn. The most common "hollow" particle was 30–32 nm in diameter with an electron-dense shell about 8 nm thick and, in some cases, a dense core granule about 5.6 nm in diameter. These VLP were always tightly packed in orderly arrays in apparently icosahedral clusters. Such clusters occurred in the perikarya of multiterminal type II neurons and glial cells in the labial nerves, bipolar type I neurons and inner sheath cells of mechano- and chemo-sensilla on both appendages, adjacent epidermal cells, and an axon from an antennal sensillum. A second type of VLP was dense-cored and about 22 nm in diameter. This type was scattered individually or in loose, unordered clusters in a type I sensillar neuron. Both VLP types were closely associated with ribosomes. Some minor cytopathic changes in the contents of cells containing VLP, and the occurrence of VLP as manifestations of physiological stress rather than as infective virions, are discussed.