Influence of nitrogen fertility and Neotyphodium endophyte strain on black cutworm Agrotis ipsilon Hufnagel performance, feeding behavior, and susceptibility to the insect parasitic nematode Steinernema carpocapsae (weiser) in tall fescue Schedonorus arundinaceus (schreb.) dumort
Abstract
Because of the high degree of variability in expression of endophyte-mediated resistance and a less than thorough understanding of the factors driving this variability, there is presently no scientifically established framework for integrating endophyte-mediated host-plant resistance into turfgrass IPM programs. Endophyte-mediated insect resistance depends on defensive alkaloids, which may deter insect feeding (antixenosis), or reduce insect performance (antibiosis). Because of their effects on insect herbivores, Neotyphodium endophytes may also influence interactions between these insects and their natural enemies. The present thesis focuses on two potentially important sources of variation in endophyte-mediated resistance, 1) inherent genetic variation associated with different grass cultivar × endophyte haplotype (strain) combinations, and 2) variation resulting from differential N availability, and explores how these factors interact to influence black cutworm performance and susceptibility to an insect parasitic nematode. Findings of this research reinforce the idea that N fertility inputs and endophyte infection may interact to influence the suitability of a grass to its insect herbivores. In a series of screening trials, the endophyte-mediated alkaloid, N-acetyl norloline, was identified as a potentially useful source of resistance to black cutworm Agrotis ipsilon Hufnagel. Because loline alkaloids are not known to be toxic to vertebrates, endophyte infected grasses that feature these toxins should also be relatively safe for wildlife and grazing animals a characteristic that could be important for the development of sustainable turfgrass management systems. The endophyte strains used in this study, and their associated alkaloid profiles did not negatively affect black cutworm susceptibility to the insect-parasitic nematode Steinernema carpocapsae (Weiser), presumably because of the lack of ergot alkaloid production in these endophyte strains. Therefore, unlike results of previous studies indicating antagonistic interactions between common endophyte strains and insect parasitic nematodes, the present study opens the door for successful incorporation of these two biologically-based pest management tools in turfgrass IPM programs targeting black cutworm.
Degree
M.S.
Advisors
Richmond, Purdue University.
Subject Area
Agronomy|Entomology|Agriculture
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