Observations on the Susceptibility of Some Insects to Nosema (Microsporidia: Sporozoa)

Abstract

A species of Nosema isolated from Tribolium will also infect per os Tenebrio molitor, Galleria mellonella, and Bombyx mori. Nymphs of Blaberus craniifera, Byrsotria fumigata, and Periplaneta americana as well as larvae of G. mellonella, B. mori, Hyalophora cecropia, and Tribolium are susceptible to the parasite when it is introduced surgically. Spores recovered from surgically infected H. cecropia remain infective per os for Tribolium. The susceptibility of the various hosts is discussed with respect to the condition of the host's alimentary canal. Successful parasitism may be considered a sequence of events consisting of entrance, establishment, emergence, and transmission (Smith, 1921). Chandler and Read (1961, p. 19) point out that three conditions determine and delimit the conditions of specificity, i.e., access of the parasite to the host, the ability of the parasite to establish itself when it gains entrance, and satisfactory conditions for growth and reproduction after the parasite is established. Host susceptibility is mainly a function of the last two of these conditions. The factors controlling these phases are not fully understood in most instances (Read, 1958). We have undertaken to clarify some of the interrelationships in the susceptibility of various hosts to the microsporidian, Nosema. There is a strong tendency to regard the Microsporidia parasitic in mosquitoes as strongly host-specific (Kudo, 1924); however, Fantham and Porter (1913) infected 13 other species of insects with Nosema apis, a species which normally infects Apis mellifera, the honeybee. Among the insects infected was Bombus sp., a bumblebee, which reportedly possesses its own species of Nosema. Steinhaus and Hughes (1949) reported that N. destructor will infect ten different hosts from three orders of insects. Finlayson and Walters (1957) infected eight species of insects with a Nosema sp. originally isolated from Hyalophora cecropia, and Dissanaike (1958) inReceived for publication 21 May 1962. * Present address: Department of Biology, Rice University, Houston, Texas. fected an oribatid mite and a cestode with N. helminthorum. Kudo and DeCoursey (1940), and more recently Verber and Jasic (1961), found that N. bombycis will infect Hyphantria cunea as well as its reported host Bombyx mori. Nosema bombycis is also said to infect Arctia caja (Stempell, 1909) and Margarnia pyloalis and Chilo simplex (Ohshima, 1935). In the present study we have undertaken successfully to establish a microsporidian parasite, Nosema, in a group of insects which do not normally represent satisfactory host species, and in so doing to delimit and elucidate some of the aspects of host susceptibility concerning this parasite and its insect hosts. MATERIALS AND METHODS The sporozoan concerned in this investigation was Nosema whitei, Weiser, identified by Dr. J. P. Kramer of the Illinois Natural History Survey, Urbana, Illinois, which normally infects flour beetles of the genus Tribolium. It should be pointed out that Thompson (1960) considers Nosema whitei as invalid; however, Weiser (1961) contends that the species is valid. In this paper the parasite will be referred to as Nosema. West (1960) reported on the biology and morphology of this parasite. Spores obtained from moribund larvae or larvae which died from the Nosema disease were pulverized and mixed with the Tribolium culture medium. Spore concentrations of 104/g of flour proved to be the most effective in maintaining large numbers of infected larvae. The insects utilized in this investigation were purchased from commercial suppliers, provided by other investigators, or raised in our laboratory. All species raised under laboratory conditions were maintained at 27 to 29 C with a relative humidity