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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGY AND MANAGEMENT OF GRASSHOPPERS AND OTHER INSECT PESTS IN THE NORTHERN GREAT PLAINS

Location: Pest Management Research Unit

Title: Effects of genotypic variation in stem solidity on parasitism of a grass-mining insect

Authors
item Rand, Tatyana
item Waters, Debra
item Shanower, Thomas
item Berzonsky, William -

Submitted to: Basic and Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 2012
Publication Date: April 10, 2012
Repository URL: http://handle.nal.usda.gov/10113/54506
Citation: Rand, T.A., Waters, D.K., Shanower, T.G., Berzonsky, W.A. 2012. Effects of genotypic variation in stem solidity on parasitism of a grass-mining insect. Basic and Applied Ecology. 13(3):250–259.

Interpretive Summary: A major goal in applied pest-control research has been to determine whether breeding for host plant resistance traits can be combined with biological control to develop a truly integrated management approach. An important component of such a project involves understanding how crop resistance traits affect the effectiveness of potential biological control agents. In this study, we examined the influence of genotypic variation in stem solidity, the dominant trait used in breeding for resistance against the wheat stem sawfly, Cephus cinctus, a major pest of cereals in the northern Great Plains of North America, on parasitism of this herbivore by parasitoid wasps. Limited evidence from this system has suggested that stem solidity does not affect parasitism of C. cinctus in wheat, however studies done in other systems have shown that stem toughness and solidity generally negatively affect parasitoid foraging and therefore effectiveness. In order to rigorously assess the influence of stem solidity on parasitism of the wheat stem sawfly, we carried out a multi-site field experiment in which we established replicate plots of both released wheat varieties and experimental lines that varied in levels of stem solidity and monitored parasitism levels over two years. We found that increasing stem solidity was associated with an approximately 4-fold reduction in average parasitism rates, both across experimental plots and across wheat varieties/lines. However, interestingly, wheat genotype also had a significant influence on levels of parasitism, independent of its effects on stem solidity. Overall, our results suggest that although increasing stem solidity generally disrupts parasitism, considerable variability in parasitism levels exists among wheat lines even within resistance categories. Thus it may be possible to select resistant solid stem varieties that better facilitate parasitism, and in so doing increasing the compatibility between resistance breeding and biological control.

Technical Abstract: Host plant traits can play a significant role in influencing the importance, direction and intensity of tri-trophic interactions via both direct and indirect pathways. A major goal in applied tri-trophic research has been to determine whether breeding for host plant resistance traits can be combined with biological control to develop a truly integrated management approach. An important component of such a project involves understanding how resistance traits affect natural enemy effectiveness. In this study, we examined the influence of genotypic variation in stem solidity, the dominant trait used in breeding for resistance against the wheat stem sawfly, Cephus cinctus, a major pest of cereals in the northern Great Plains of North America, on parasitism of this herbivore by native parasitoids. Limited evidence from this system has suggested that stem solidity does not affect parasitism of C. cinctus in wheat, however studies done in other systems have shown that stem toughness and solidity generally negatively affect parasitoid foraging success, both by reducing host location ability as well as stem penetration by ovipositing females. In order to rigorously assess the influence of stem solidity on parasitism in our system, we carried out a multi-site field experiment in which we established replicate plots of both released wheat varieties and experimental genotypes that varied in levels of stem solidity and monitored parasitism levels over two years. We found that increasing stem solidity was associated with an approximately 4-fold reduction in average parasitism rates, both across experimental plots and across wheat genotypes. Our analyses revealed that these effects were primarily directly mediated, rather than an indirect result of stem solidity effects on herbivore infestation levels or density. Interestingly, wheat genotype also had a significant influence on levels of parasitism, independent of its effects on stem solidity. Overall, our results suggest that although increasing stem solidity generally disrupts parasitism, considerable among genotype variability in parasitism levels exists, such that it may be possible to select resistant solid stem genotypes that better facilitate parasitism. To our knowledge, our study is among the first to demonstrate a strong direct effect of genotypic variation in stem morphology on parasitism of grass mining insects, with important applied implications.

Last Modified: 9/23/2014
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