The protozoa occurring in the hind-gut of cockroaches. I. Responses to changes in environment

Abstract

Records of non-sporozoan Protozoa occurring in the hind-gut of cockroaches are summarized.The Protozoa studied were the three flagellatesLophomonas striata, L. blattarum, Monocercomonoides orthopterorum; the rhizopodEndamoeba blattae, and the ciliateNyctotherus ovalis, in the cockroachesPeriplaneta americana, P. australasiae, Blatta orientalis, Blattella germanicaandBlaberus giganteus.Specimens ofBlattaandPeriplaneta americanawere maintained at 37° and 25°C. under extreme conditions of humidity. Maximum humidity enabled the host, and theNyctotheruswhich it harboured to survive for a longer time. The results of the experiments indicated that the well-being of the protozoan parasites is closely linked to that of the host.Periplaneta americana, Blatta, BlatellaandBlaberuswere subjected to pure oxygen at 3½ atmospheres pressure and the effect on the Protozoa observed. The flagellates were killed first, thenEndamoebaand lastlyNyctotherus. They survived inBlattafor a longer time than inPeriplaneta; andNyctotherusinBlaberusandBlattellasometimes survived the hosts. The hosts appeared to act as a barrier against poisoning by oxygen, and the strength of the barrier varied in the different species of cockroaches.NymphalPeriplanetaorBlattawhich were about to moult underwent a period of self-starvation which lasted for up to 10 days. The period was terminated by the moult: at this time, the little food that was in the gut was very dry. All species of Protozoa could survive these conditions, butNyctotherusseemed to be the most hardy. The main mass of ciliates seemed to be nearer to the anus than in the non-moulting cockroach. Many of the ciliates were often clumped together into a ‘raspberry’. The bodies of the individual ciliates were more spherical than usual, but those in the ‘raspberry’ were moulded into polygonal shapes. The macronucleus underwent a change in form which revealed that its basic structure is that of a folded sheet.The changes were reversed within 24 hr. They could not be induced by experimentally imposed conditions of starvation or dehydration of the hind-gut. The changes inNyctotherus ovalisare contrasted with the sexual stages occurring inN. cordiformisand in the Protozoa ofCryptocercus.This work was done during the tenure of a Research Studentship awarded by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work. I wish to thank Drs J. Barker and E. R. Turner, of the Cambridge University Botany School, for the loan of the apparatus used in subjecting cockroaches to oxygen under pressure, and Mr A. C. Bloy, of the Zoology Department, for gifts of cockroaches. I am most grateful to Mrs E. F. M. Hawkins and Mr B. H. Baker for technical assistance.