Location: Pest Management Research Unit
Title: Increased area of a highly suitable host crop increases herbivore pressure in intensified agricultural landscapes Authors
Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 28, 2014
Publication Date: March 15, 2014
Repository URL: http://handle.nal.usda.gov/10113/58595
Citation: Rand, T.A., Waters, D.K., Blodgett, S.L., Knodel, J.J., Harris, M.O. 2014. Increased area of a highly suitable host crop increases herbivore pressure in intensified agricultural landscapes. Agriculture, Ecosystems and Environment. 186: 135-143. Interpretive Summary: Although the domination of agricultural landscapes by one or two crops is a major component of agricultural intensification with important potential effects on pest insects, it has not been well studied compared with the many studies showing lower numbers of natural enemies such as predators and parasites in areas with little natural habitat remaining. Here we found significant increases in levels of infestation by a dominant pest in wheat, the wheat stem sawfly Cephus cinctus, in response to increasing wheat acreage at the landscape scale. This pattern was consistent across six study regions spanning the Northern Great Plains of North America, despite large differences in cropping systems and levels of infestation across regions. In contrast, increasing acreage in natural habitats had no significant independent effects on either sawfly infestation or parasitism of this pest by common natural enemies, the parasitoid wasps Bracon cephi and Bracon lissogaster. Regional differences in pest pressure were best explained by long term averages in rainfall, with infestation tending to be higher in drier regions. Our results suggest that increasing wheat stem sawfly infestation in this system results from a direct response of the sawfly to increasing acreage of a preferred crop, rather than reductions in control by natural enemies resulting from reductions in acreage of natural habitats such as rangeland. Thus reducing the amount of wheat acreage at the landscape scale, for example by planting non-host crops such as peas and lentils, or placing more land into non-crop habitats such as CRP, could directly suppress sawfly numbers and reduce infestation.
Technical Abstract: tLandscape simplification associated with agricultural intensification has important effects on economi-cally important arthropods. The declining cover of natural and semi-natural habitats, in particular, hasbeen shown to reduce natural-enemy attack of crop pests, but also in some cases reduced crop coloniza-tion by such pests. In this study, we examined the influence of changes in two elements of landscapecomposition, natural grassland cover and cover of a highly suitable crop host, on infestation by a gen-eralist insect pest in wheat, and parasitism of this pest by its dominant natural enemies. Surprisingly,we found no significant influences of increasing natural grassland habitat, at either local or landscapescales, on infestation by the wheat stem sawfly, Cephus cinctus, or parasitism of this pest by the nativeparasitoid wasps, Bracon cephi and Bracon lissogaster. In contrast, we found significant increases in levelsof C. cinctus infestation with increasing wheat cover at the landscape scale. This pattern was consistentacross six study regions spanning three states in the northern Great Plains of North America, despite largedifferences in cropping systems and pest population densities across regions. Regional variation in pestinfestation was best explained by long-term averages in precipitation, with higher C. cinctus infestationrates found in drier regions. Results suggest that landscape-mediated variation in pest pressure in thissystem is better explained by a direct response of pest insects to increasing cover of a highly suitable croprather than an indirect response via reductions in natural enemies as natural habitat declines. The impli-cation is that habitat diversification at the landscape scale could play a role in suppressing agriculturalpest populations via reductions in area of suitable crop hosts.