Granivorous invertebrates and weed seed predation: An ecological approach to weed management
Open Access
- Author:
- Law, Jeffrey James
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 31, 2012
- Committee Members:
- Robert Paul Gallagher Iii, Dissertation Advisor/Co-Advisor
Tomas Carlo, Dissertation Advisor/Co-Advisor
Shelby Jay Fleischer, Committee Member
John Frazier Tooker, Committee Member
Timothy Leslie, Special Member - Keywords:
- carabidae
min-till
agroecology
seed predation
Harpalus - Abstract:
- The objective of this dissertation is to better understand invertebrate agricultural weed seed predation and determine if predator olfaction and seed imbibition are important aspects of this interaction. Equally important, this project independently examines the use of a minimum tillage regime and as part of a larger integrated weed management strategy, including cover crops, to determine the influence of these management tactics on invertebrate activity-densities and weed seed predation. The minimum tillage regime did not reduce weed seed predation by invertebrates when compared to a no-till system. The majority of granivorous invertebrates had significantly higher activity-densities in minimum tillage plots when compared to no-till plots. However one species, Harpalus pensylvanicus DeGeer, an abundant seed predator, had a significant decrease in activity-density in min-till plots when compared to no-till. The integration of cover crops into a minimum tillage corn/soybean cropping system resulted in an increase in beneficial invertebrate activity-densities but did not increase surface seed predation when compared to no-till and organic systems. Through a novel application of a stable isotope, 15N, it was shown that H. pensylvanicus individuals frequently eat both velvetleaf (Abutilon theophrasti Medic) and giant foxtail (Setaria faberi Herrm) seeds in a no-till field. Imbibition of seeds altered H. pensylvanicus seed selection and the amount of seed eaten. All 7 weed seed species used in the study were eaten in significantly greater amounts when imbibed than when dry. Substantial amounts of large-sized seeds were eaten when imbibed but not when dry. Further illustrating the importance of imbibition, H. pensylvanicus individuals were shown to find imbibed velvetleaf (Abutilon theophrasti Medic) and giant foxtail (Setaria faberi Herrm) seed through olfaction but were unable to locate dry seed. Ethylene and carbon dioxide were released from dry seeds with greater amounts of these two chemicals released when seeds were imbibed. However, H. pensylvanicus beetles showed no attraction response when exposed to these chemicals in y-tube olfactometry assays. This research shows that the application of a minimum tillage regime is not detrimental to the granivorous invertebrate community or seed predation when compared to a no-till system. The integration of cover crops into this tillage regime results in an increase in beneficial invertebrate activity-densities and does not decrease surface seed predation when compared to no-till and organic systems. Olfaction and seed imbibition are important aspects of H. pensylvanicus seed selection and predation.