Joseph V. Maddox

Small subunit ribosomal DNA phylogeny of various microsporidia with emphasis on AIDS related forms.

ABSTRACT. Phylogenetic analysis of the small subunit ribosomal DNA of a broad range of representative microsporidia including five species from humans (Enterocytozoon bieneusi, Nosema corneum, Septata intestinalis, Encephalitozoon hellem and Encephalitozoon cuniculi), reveals that human microsporidia are polyphyletic in origin. Septata intestinalis and E. hellem are very similar to the mammalian parasite E. cuniculi. Based on the results of our phylogenetic analysis, we suggest that S. intestinalis be designated Encephalitozoon intestinalis. Furthermore, analysis of our data indicates that N. corneum is much more closely related to the insect parasite Endoreticulatus schubergi than it is to other Nosema species. This finding is supported by recent studies which have shown a similarity between E. schubergi and N. corneum based on the origin and development of the parasitophorous vacuole. Thus these opportunistic microsporidian parasites can originate from hosts closely or distantly related to humans. Finally, the phylogeny based on small subunit ribosomal DNA sequences is highly inconsistent with traditional classifications based on morphological characters. Many of the important morphological characters (diplokaryon, sporophorous vesicle, and meiosis) appear to have multiple origins.

Lethal and sublethal effects of Nosema pyrausta on the European corn borer (Ostrinia nubilalis) in central illinois

Abstract Sublethal and lethal effects of Nosema pyrausta were evaluated in a series of experiments with both field-collected and laboratory populations of Ostrinia nubilalis. Corn borer adults infected with N. pyrausta laid 33% fewer egg masses than uninfected adults. Transovarially infected larvae experienced higher mortality than uninfected larvae. Mortality was linked to the ovipositional sequence of the egg masses; larvae from infected egg masses laid after the fourth day of oviposition experienced greater mortality than those from infected egg masses laid during the first 2 days of oviposition. Both cold stress and crowding stress increased mortality of infected larvae. Spore dosage experiments were conducted using first- and third-instar larva; first-instar larvae had the highest IC50 (concentration of spores at which 50% of the larvae became infected), 26 spores/mm2 diet surface.

Phylogenetic Position of Amblyospora Hazard & Oldacre (Microspora: Amblyosporidae) Based on Small Subunit rRNA Data and Its Implication for the Evolution of the Microsporidia

ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced.

Impact of Nosema pyrausta on a braconid, Macrocentrus grandii, in central Illinois

Abstract In the course of a 4-year study of the epizootiology of Nosema pyrausta in the European corn borer, Ostrinia nubilalis , the braconid Macrocentrus grandii was recovered from the corn borer. Some of the braconids were also infected with N. pyrausta , and the level of N. pyrausta in the corn borer corresponded to the level of infection in the parasitoid. N. pyrausta infection reduced both the number of braconids exiting the corn borer host as well as adult emergence of M. grandii . Infected M. grandii females were able to transmit N. pyrausta to their progeny as well as serve as vectors for the pathogen in the laboratory.

Modeling the effects of the microsporidium, Nosema pyrausta, on the population dynamics of the insect, Ostrinia nubilalis)

Abstract We created a comprehensive ecological model to simulate the long-term population dynamics of Ostrinia nubilalis under the influence of Nosema pyrausta . Results demonstrated that, when the pathogen persists, it can regulate the corn borer population far below the carrying capacity of the maize environment. When we included the typical assumption of a homogeneous or uniform spatial distribution of hosts in the model, disease prevalence tended to fluctuate in cycles. Mechanistic modeling of spatial dynamics to produce spatial heterogeneity resulted in convergence to a steadystate level of prevalence. Sensitivity analysis indicated that spore dissemination and the timing of processes are important. The validation effort was inconclusive but did show the significance of temperature and latitude for the population dynamics.

Seasonal progress of Nosema pyrausta in the European corn borer, Ostrinia nubilalis

Abstract A 4-year study of the epizootiology of Nosema pyrausta in the European corn borer, Ostrinia nubilalis, was conducted in Woodford County, Illinois, during 1980–1983. N. pyrausta infections in the first-generation larvae resulted primarily from transovarial infection. Second-generation N. pyrausta larval infections resulted from both transovarial infection and horizontal transmission. There was a significant relationship between larval density and percentage infection of N. pyrausta for the second generation, whereas no such relationship could be demonstrated for the first generation. We attempted to determine empirically a critical density for horizontal transmission in the second generation and concluded that no single threshold value existed.

Timing of disease-influenced processes in the life cycle of Ostrinia nubilalis infected with Nosema pyrausta

Abstract The timing of events in the life cycle of the European corn borer, Ostrinia nubilalis, can be important in the transmission and spread of the chronic disease caused by the microsporidium Nosema pyrausta. We performed two experiments with transovarially infected larvae to investigate the dynamics of the disease. In the first study, mean developmental times of infected and uninfected insects reared at 30°C were not significantly different; however, the disease significantly slowed the development of second- to fifth-instar larvae and pupae reared at 24°C. In the second study, the production of spores in the excrement of larvae increased exponentially from hatch to pupation.

Spatial and temporal dynamics of animals and the host-density threshold in epizootiology

Abstract The concept of a host-density threshold, commonly discussed in theoretical epidemiology and epizootiology, is based on simple theoretical models and several vague definitions. We computed a more complex model on a supercomputer to study the temporal and spatial dynamics of an insect population and its microsporidian disease. Results demonstrated that the threshold is sensitive to initial prevalence of the disease, intragenerational temporal dynamics, and spatial dynamics of the host. The threshold also depends on whether pathogen persistence, an increase in prevalence, an increase in density of infected hosts, or an epidemic is being predicted. To improve epizootiological theory, models with greater realism must be studied and the concept must include general temporal and spatial scales.

Long-term storage of infective microsporidian spores in liquid nitrogen

Thirty‐one species of microsporidia, isolated from insects and stored in liquid nitrogen for up to 25 yr, were infectious when removed from liquid nitrogen. The natural hosts of all of these microsporidia were terrestrial insects, representing six different insect orders: Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera. All microsporidia from terrestrial insects that were tested survived storage in liquid nitrogen, while Nosema algerae, a microsporidium from aquatic mosquito hosts did not survive freezing in liquid nitrogen. A Nosema species from the alfalfa weevil, Hypera postica, lost some infectivity in a water storage medium after 25 yr in liquid nitrogen. Liquid nitrogen storage of microsporidian spores in 50% and 100% glycerol media reduced loss of infectivity and is recommended for extended storage of microsporidia from terrestrial insect hosts.

Effect of temperature on distribution and success of introduction of an Empoasca fabae (Homoptera: Cicadellidae) isolate of Erynia radicans (Zygomycetes: Entomophthoraceae)

Abstract Empoasca fabae is a serious leafhopper pest of agriculturally important crops in the midwestern and northeastern United States. The geographic distribution of Erynia radicans , a fungal pathogen of E. fabae , led us to examine the effects of temperature on tn vitro and in vivo growth and conidial germination of E. radicans . In addition, we examined the effects of temperature on the establishment of E. radicans in the field. E. radicans grew at constant temperatures of 28°C and below, both in vivo and in vitro, but did not grow at 30°C or above. Conidial germination followed a similar pattern; however, E. radicans survived exposure periods of up to 24 hr at 32°C in vivo. E. radicans did not cycle through a caged population of E. fabae in a growth chamber at 22°C despite the occurrence of infections immediately following fungal release. E. radicans did not become established after introduction into field populations of E. fabae at three sites in Illinois. We observed initial infections of leafhoppers at two of these sites and evidence suggests that horizontal transmission occurred at one of them. Epizootics, however, did not occur despite high populations of leafhoppers. Temperatures exceeded the laboratory thresholds for growth of E. radicans at each of the three sites during the first week after release, but for different durations.