The role of margins in herbivore and natural enemy abundance within Michigan celery fields

Michigan ranks in the top three states for celery production with 52,000 tons harvested from 1800 acres and a market value of approximately $20 million. Despite the economic importance, there is a lack of published information on insect community ecology within these agroecosystems. Celery fields in Michigan are dynamic environments subjected to disturbances with regular frequency. These fields experience near-weekly episodes of extinction and recolonization by many arthropod taxa as a result of broad-spectrum insecticides. Field margins in celery systems, however, are managed less intensively than the crop and could serve as both a refuge from disturbance and a subsequent source for field recolonization. The objectives of this study were to (1) examine the arthropod community in Michigan celery agroecosystems and (2) investigate the use of field margins by herbivores and natural enemies. Transects for sticky traps and foliage inspection were established within six commercial celery fields located in three southwest Michigan counties. Samples were taken weekly throughout the growing season; captured arthropods were identified to the lowest possible taxonomic unit. Spatiotemporal abundance was recorded and evaluated using analysis of variance. To detect movement of arthropods from field margins into the crop, a mark-capture experiment was implemented by spraying crude egg proteins onto vegetation within the margins. Herbivores and natural enemies were collected accordingly and subjected to an ELISA to test for presence of the protein marker. The proportion of marked taxa was recorded along with their spatial location within the system and evaluated with regression and analysis of variance.