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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: Tritrophic interactions among Bt maize, an insect pest and entomopathogens: effects on development and survival of western corn rootworm

Authors
item Petzold-Maxwell, Jennifer -
item Jaronski, Stefan
item Gassman, Aaron -

Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 3, 2011
Publication Date: November 9, 2011
Repository URL: http://handle.nal.usda.gov/10113/56794
Citation: Petzold-Maxwell, J.L., Jaronski, S., Gassman, A.J. 2012. Tritrophic interactions among Bt maize, an insect pest and entomopathogens: effects on development and survival of western corn rootworm. Annals of Applied Biology. 160(1): 43-55.

Interpretive Summary: Agricultural systems often provide a model for testing ecological hypotheses, while ecological theory can enable more effective pest management. One of the best examples of this is the interaction between host-plant resistance and natural enemies. Plant resistance traits that alter pest behavior or physiology (i.e., slower developmental rate or increased searching time) can lead to enhanced attack by natural enemies, resulting in synergism; conversely, antagonistic interactions can arise when host-plant resistance traits have direct negative effects on enemies by increasing mortality. Or, natural enemies and host-plant resistant factors can act independently on insect populations, resulting in either complementary or opposing effects. An extensive gap in our knowledge exists for below-ground tritrophic interactions. With the advent of crops that are genetically modified to produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt), a new form of host-plant resistance has been introduced to agro-ecosystems, notably corn and cotton in the U.S. How Bt crops interact with natural enemies, especially insect pathogens in below-ground systems, to affect a target insect is not well understood, but provides a unique opportunity to study the broader topic of below-ground tritrophic interactions. In this study, we used a community of insect pathogens ( 2 fungi and 3 nematode species) to determine how these soil-borne natural enemies interact with Bt maize and the target pest insect, the western corn rootworm (Diabrotica virgifera virgifera). The community of entomopathogens significantly increased mortality of western corn rootworm, and Bt maize increased larval developmental time and mortality. The insect pathogens and Bt maize acted in an independent and complimentary manner to reduce abundance of western corn rootworm. Results from this study suggest that entomopathogens may complement host-plant resistance factors in natural and agricultural systems by leading to greater mortality of insects.

Technical Abstract: Agricultural systems often provide a model for testing ecological hypotheses, while ecological theory can enable more effective pest management. One of the best examples of this is the interaction between host-plant resistance and natural enemies. With the advent of crops that are genetically modified to produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt), a new form of host-plant resistance has been introduced to agroecosystems. How Bt crops interact with natural enemies, especially insect pathogens in belowground systems, is not well understood, but provides a unique opportunity to study below-ground tritrophic interactions. In this study, we used two species of entomopathogenic fungi and three species of entomopathogenic nematodes to determine how this community of soil-borne natural enemies might interact with Bt maize (event 59122, expressing the insecticidal protein Cry34/35Ab1) to affect survival and development of western corn rootworm (Diabrotica virgifera virgifera), which is an obligate root feeder and a serious pest of maize. We ran two experiments, one in a greenhouse and one in a growth chamber. Both experiments consisted of a fully crossed design with two maize treatments (Bt maize and non-Bt maize) and two entomopathogen treatments (present or absent). The community of entomopathogens significantly increased mortality of western corn rootworm, and Bt maize increased larval developmental time and mortality. Entomopathogens and Bt maize acted in an independent and additive manner, with both factors increasing the mortality of western corn rootworm. Results from this study suggest that entomopathogens may complement host-plant resistance from Bt crops.

Last Modified: 12/20/2014