Dynamics of Nosema pyrausta in natural populations of the European corn borer, Ostrinia nubilalis: A six-year study

Abstract

Nosema pyrausta (Paillot) (Microsporida: Nosematidae) is an obligatory intracellular parasite of the European corn borer, Ostrinia nubilalis (Hu¨bner) (Lepidoptera: Crambidae). This pathogen is maintained in natural populations of O. nubilalis by both horizontal and vertical transmission. The impact of N. pyrausta on fecundity of adults and survival of larvae has been well documented in laboratory and field research. In an extensive study covering a 6 year period at one site, we described the effect of N. pyrausta within O. nubilalis populations in a continuous corn following corn ecosystem. We documented the presence of the pathogen through all life stages of O. nubilalis (egg, larva, pupa, adult), by collecting throughout the crop season and examining each insect stage in the laboratory for the frequency of infection with N. pyrausta. The percentage of infection with N. pyrausta and magnitude of the O. nubilalis population fluctuated throughout generation 1 and generation 2. Both horizontal and vertical transmission played a role in maintaining N. pyrausta in the population in both generations. There were strong correlations between percentage adults with N. pyrausta and percentage larvae with N. pyrausta, and between percentage eggs with N. pyrausta and percentage larvae with N. pyrausta. There was a weak correlation between percentage adults with N. pyrausta and percentage eggs with N. pyrausta. The percentage of insects infected with N. pyrausta was always lowest in the egg.

Microsporidia Biological Control Agents and Pathogens of Beneficial Insects

“…Prevalences of N. pyrausta among ECB larvae in various studies have fluctuated from 2 to 100% resulting in both enzootic and epizootic phases, and were associated with declines in ECB populations (Hill & Gary 1979;Andreadis 1986;Siegel et al 1988; Lewis et al 2006). Despite the sustained presence of N. pyrausta, ECB damage still occurs and compels utilization of other control methods.…”

“…Its life cycle and efficient vertical and horizontal transmission integrate well into the phenologies of the ECB and corn. While applications of spore solutions can initiate field infections of N. pyrausta, the lack of in vitro mass production methods limits further development as a microbial insecticide (Lewis et al 2006). Nevertheless, N. pyrausta is an important factor regulating ECB populations with epizootics cycling every 6-7 years (Lublinkhof et al 1979;Lewis et al 2009).…”

Effects of combining Beauveria bassiana and Nosema pyrausta on the mortality of Ostrinia nubilalis

“…9,[20][21][22][23]. Nosema pyrausta Paillot (Microsporida, Nosematidae) is a common and widespread obligate intracellular parasite of ECB and plays an important role in suppressing its population levels [e.g.…”

“…Nosema pyrausta Paillot (Microsporida, Nosematidae) is a common and widespread obligate intracellular parasite of ECB and plays an important role in suppressing its population levels [e.g. 8,21,24]. ECB is the only lepidopteran reported to be naturally infected with N. pyrausta [24].…”

“…The pathogen spreads horizontally in host populations through ingestion of spores and vertically via transovarial mechanism [25]. All life stages of ECB can be affected [21] and N. pyrausta can regulate ECB populations well below the environmental carrying capacity [26]. However, the timing of infection is important in determining what effect the microsporidium has on its host [27].…”