Ruth Leutenegger

Ultrastructural investigation of the melanization process in Culex pipiens (Culicidae) in response to a nematode

The present account is an ultrastructural investigation on the formation of a melanized sheath around third stage infective juveniles of Neoaplectana carpocapsae Weiser within the larval hemocoel of Culex pipiens L. The host reaction began almost immediately after the nematode entered the body cavity of the mosquito larva. Within 1 hour, a homogeneous matrix or deposit surrounded the nematode. After being in the host for 1–2 hours, minute pigment granules formed within the homogeneous matrix, and they eventually enlarged and coalesced to form a layer of melanin around the parasite. The normal definitive capsule appeared in 5–10 hours and was composed of an inner melanized region, a middle non- or slightly melanized homogeneous layer and an outer region containing tracheole elements and cellular debris. It appeared that the homogeneous matrix in which the melanin was eventually produced did not arise from blood cells, but from components in the noncellular portion of the hemolymph that coagulated out on the surface of the nematode. This reaction could then be considered an example of humoral melanization in contrast to the more common hemocytic melanization involving the hosts blood cells.

Ultrastructure of the formation of a melanotic capsule in Diabrotica (Coleoptera) in response to a parasitic nematode (Mermithidae).

The present paper is an ultrastructural study of the formation of a melanotic capsule in the beetles Diabrotica balteata and D. u. undecimpunctata , in response to the mermithid nematode Filipjevivermis leipsandra . Soon after the infective stages of F. leipsandra entered the body cavity of third stage Diabrotica larvae, they were encapsulated by host blood cells and subsequently killed. Initial hemocytes making contact with the parasite lysed and liberated their cytoplasm over the nematodes cuticle. Within 6–8 hours, the inner layer of cytoplasm was replaced by an electron dense material, probably melanin. The definitive 72-hour capsule was composed of four major regions; (a) an inner partially melanized region, (b) a layer of spherical, necrotic cells, (c) a region containing 3–4 layers of very elongate cells, and (d) an outer zone consisting of loosely attached hemocytes bearing close resemblance to normal blood cells.

Multiplication of a granulosis virus in larval midgut cells of Trichoplusia ni and possible pathways of invasion into the hemocoel.

The ultrastructure of the midgut epithelium of the fourth-instar cabbage looper larva of Trichoplusia ni has been described. The epithelium consists of columnar and goblet cells. A granulosis virus of T. ni infects and multiplies in columnar midgut cells and in fat cells. The goblet cells appear not to be infected. Complete virus particles with developmental (or outer) membranes have been found, 24 hours after virus ingestion, in some of the intercellular spaces between midgut cells. There is evidence of virus multiplication in the nuclei of columnar cells as early as 24 hours after virus ingestion. A few virus particles occur in the cytoplasm near the bases of the microvilli, but most are found in the basal portion of the cytoplasm of the infected cells. Some particles also appear in the intercellular spaces at the bases of the columnar cells and in the basement membrane. The infected midgut cells contain “naked” and complete virus particles, but very rarely virus inclusion bodies (capsules). Occasionally hexagonal inclusions occur in virus-infected cells, but they do not seem to have virus particles in them. Based on these observations, we have postulated two pathways by which the ingested granulosis virus may invade into the hemococl of the cabbage looper larva.

Early events of Sericesthis iridescent virus infection in hemocytes of Gallerio mellonella (L.)

Abstract The early stages of infection of insect blood cells by Sericesthis iridescent virus (SIV) were studied. Blood cells of Galleria mellonella (L.) infected with SIV at 22° were sampled at different intervals and then subjected to electron microscopy and high-resolution autoradiography. At 2 hours post inoculation virus was found inside the cells within phagocytic vesicles. A large proportion of virus had disappeared after all incubation period of 3 hours. Viral DNA synthesis in the cytoplasm was demonstrated as early as 4Y2 hours post SR inoculation by using tritiated thymidine and autoradiography. Earliest occurrence of progeny virus within foci was found to be at 12 hours. Decrease in nuclear incorporation of thymidine 3H indicates all interference of normal nuclear DNA synthesis in the course of SIV infection.

The fine structure of the trophic cells of Perilitus coccinellae (Hymenoptera: Braconidae)

Some aspects of the fine structure of trophic cells associated with the braconid parasite Perilitus coccinellae are described. Morphological changes in those cells as they age and hypertrophy are considered. Suggestions are made which correlate these morphological changes with functional changes in these trophic cells.

Histopathology of a granulosis-virus disease of the codling moth, Carpocapsa pomonella.

Abstract The granulosis of the codling moth, Carpocapsa pomonella , is a polyorganotropic disease and produces pathologies in the fat body, hypodermis, tracheal matrix, and Malpighian tubules. Both free virus rods and capsules were observed in these organs with the electron microscope. The occurrence of infection in the Malpighian tubules suggests that the virus may be excreted through this organ. Laboratory tests indicated this possibility, but fecal contamination was not conclusively established. In addition to the virus rods and capsules found in the cells in an advanced stage of infection, there was a mass of coiled filaments that may be associated with the formation of the virus rods.

Development of an icosahedral virus in hemocytes of Galleria mellonella (L.)

Abstract The proliferation of an icosahedral virus in insect hemocytes was studied by means of electron microscopy of ultrathin sections. Evidence is presented that virus development occurs in the cytoplasm.