Histopathology of secondary infections of Malpighamoeba locustae (Protozoa, Amoebidae) in the desert locust, Schistocerca gregaria (Orthoptera, Acrididae)

Abstract

Schistocerca gregaria, the desert locust, harbors the protozoan parasite Malpighamoeba locustae. Twelve to 16 days after infection, trophozoites begin to multiply rapidly inside the Malpighian tubules of the gut. Swelling and rupture of the Malpighian tubules leads to the release of large numbers of cysts and trophozoites into the hemocoel. The classic insect defense response results in these cysts and trophozoites becoming encapsulated by the hemocytes of the host. Hemocytes of the phagocytic type become attached to, and lodged between, a variety of tissues and organs of the locust and black hemocytic capsules are produced. The extent to which the different tissues are involved is graded. Some tissues are completely blackened and encapsulated by masses of hemocytes but others are so lightly affected that the small specks of blackened pigment they lay down are discernible only on close examination. The trophozoites themselves do not divide outside the Malpighian tubules. The graded response in the host tissues is related to (1) the presence of sheets and lobes of fat body and (2) the presence of phagocytic hemocytes.