THE LIFE HISTORY OF MALAMEBA LOCUSTAE (KING AND TAYLOR) IN THE MIGRATORY GRASSHOPPER MELANOPLUS SANGUINIPES (F.)

Abstract

Using both light and electron microscopy, the structure and life history of the protozoan Malameba locustae (King and Taylor) was studied in the migratory grasshopper Melanoplus sanguinipes (F.). The ultrastructure of trophozoites in both midgut and Malpighian tubules was described. Trophozoites ranged in size from 7-11 pm. The cytoplasm contained a nucleus with a prominent nucleolus, many mitochondria with tubular cristae, numerous lipid drops, extensive RER and several autophagic vacuoles. Binucleate trophozoites were common in the tubule lumen. As trophozoites matured they became rounded, and the cytoplasm became condensed, obscuring most of the cell organelles. Numerous small vesicles appeared just inside the cell membrane, and this was followed by the layered deposition of cyst wall material. The completed cyst wall was highly refractive and about 0.5 pm thick. Insects fed cysts had developed infection in the Malpighian tubules when examined 5 to 6 days later. However, no trophozoites were seen in haemolymph samples taken 2 days to 20 days post-feeding. After excystment, a few trophozoites entered midgut epithelium where they usually were extracellular. Many of those trophozoites in midgut epithelium were located near the basement membrane of the epithelial cells, where they appeared to degenerate. Trophozoites were not seen to divide in the midgut epithelium, and apparently did not damage the host tissue. Trophozoites injected directly into the haemocoel could not be recovered even 4 h after injection, and the Malpighian tubules did not become infected. It was concluded that trophozoites did not penetrate the midgut to enter the haemocoel or move through the haemocoel to infect the Malpighian tubules, but instead entered the tubules directly from the gut.