Pathological studies on the cockroach : I. Spontaneous occurrence of hindgut ulcer in the smoky-brown cockroach, Periplaneta fuliginosa (Serville)

Abstract

It is known that tumor-like lesions of the alimentary canal have been experimentally induced in cockroaches and locusts by nerve severance, duct ligation, decapitation, etc. The similar lesions have been known to occur spontaneously in less than 10 percent of these insects in nature. We have recently found the same kind of lesion in more than 80 percent of our laboratory colony of Periplaneta fuliginosa (Serville). The roaches bearing the lesion were abnormally distended or swollen in their abdomens filled with whitish fat bodies. At autopsy, this lesion was easily recognized as a white opaque mass against the normal brownish tissue. Histologically, tracheation and pigmented necrotic foci were seen in the lesion, and around it hundreds of hemocytes aggregated to give an appearance of tumor. The nuclei of the peripheral cells were located near the inner bound-aries, but no mitosis was observed. These figures suggest that the lesion is not of neoplasmic nature but a sort of repairing process of injury; we now regard it as a kind of ulcer. Field surveys conducted around Nagoya City in 1975-1976 revealed that the overall mean incidence of the lesion among the natural populations of P. fuliginosa was about 17 percent. But it differed by the collection sites, ranging from 3 to 65 percent. It did not noticeably change by the seasons of the year. However, the morbidity in the female (ca. 34%) was significantly higher than those in the male (ca. 13%) or larva (ca. 12.5%). Laboratory rearing of the cockroaches collected in nature seemed to increase their morbidity up to 90 percent or more, and the high morbidity resulted in high mortality with little exceptions. This tendency was more definitely shown when the roach was reared individually.