Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Laboratory assays were conducted to study the impact of pathogenic infections of black cutworm (BCW), Agrotis ipsilon (Hufnagel) and European corn bearer (ECB), Ostrinia nubilalis (Hubner) on their parasitoid species Bonnetia comta (Fallen) (BCW), and Lydella thompsoni Herting and Macrocentrus grandii Goidanich (ECB). Host microsporidian infections had detrimental effects on all three parasitoids. Vairimorpha necatrix (Kramer) and Vairimorpha sp. both decreased the number of B. comta able to pupate from BCW hosts, the days required for adult eclosion, and the weights of the puparia. These effects increased with an increase in the intensity of the host infection. Nosema pyrausta (Paillot) and Nosema sp. within ECB hosts reduced eclosion of adult L. thompsoni by 36 and 100%, respectively. Nosema sp. was found to infect most ECB tissues as opposed to the limited infection caused by N. pyrausta. Lydella thompsoni maggots consume most of the ECB host tissues; therefore the more severe impact that the Nosema sp. had on the parasitoid could be explained by the difference in the number of spores consumed. Similarly, V. necatrix, which infects primarily the ECB host fat body tissue, and Nosema sp., had more detrimental effects on M. grandii developing in infected hosts than did the N. pyrausta. Again, it appeared that the impact of the microsporidian on the parasitoid was a function of the pathology of the pathogen within the host and the developmental biology of the parasitoid resulting in essentially a dosage response. Vairimorpha necatrix- and N. pyrausta-infected female M. grandii were unable to transovarially transmit these pathogens to their offspring.;A nuclear polyhedrosis virus from a mint looper, Rachiplusia ou (Guenee) (RoMNPV) had no detrimental effect on B. comta or L. thompsoni developing in RoMNPV-infected BCWs or ECBs, except indirectly, when the virus killed the hosts before the parasitoids were able to emerge. The RoMNPV polyhedral inclusion bodies were found only in the gut lumen of these parasitoids.;Bacillus thuringiensis Berliner subspecies kurstaki, although not pathogenic to BCW larvae, did reduce B. comta parasitism in treated hosts. Bacillus thuringiensis spores or crystals caught in the intersegmental membranes of the BCW host cuticle may have been encountered and ingested by B. comta planidia entering the hosts, causing them to die.



Digital Repository @ Iowa State University,

Copyright Owner

Joan E. Cossentine



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143 pages

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Entomology Commons