Title of document:  Habitat eradication and cropland intensification may reduce parasitoid diversity and natural pest control services in annual crop fields

Authors: Deborah K. Letourneau, Sara G. Bothwell Allen, Robert R. Kula,  Michael J. Sharkey, John O. Stireman III

Journal’s name if any: Elementa

 Ministry/Government Agency/Organisation:  Department of Environmental Studies, University of California, Santa Cruz, California, United States ;  Systematic Entomology Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, c/o National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, United States ; Department of Entomology, University of Kentucky, Lexington, Kentucky, United States ;  Department of Biological Sciences, Wright State University, Dayton, Ohio, United State

Year of publication: 2015

Geographic focus: Global level

Main issues / topics addressed (for example: Organic vegetable, parasitoid richnes, Insect sampling, identification, and host range determinations, Habitat elimination around farms and parasitoid diversity……)

School of agroecology (if any):

Web address to original document (if any):


 California’s central coast differs from many agricultural areas in the U.S., which feature large tracts of monoculture production fields and relatively simple landscapes. Known as the nation’s salad bowl, and producing up to 90% of U.S. production of lettuces, broccoli and Brussels sprouts, this region is a mosaic of fresh vegetable fields, coastal meadow, chaparral shrubs, riparian and woodland habitat. We tested for relationships between the percent cover of crops, riparian and other natural landscape vegetation and the species richness of parasitic wasps and flies foraging in crops, such as broccoli, kale and cauliflower, and interpreted our results with respect to the decrease in natural habitat and increase in cropland cover prompted by a local microbial contamination event in 2006. Our key results are that: (1) as cropland cover in the landscape increased, fewer species of parasitoids were captured in the crop field, (2) parasitoid richness overall was positively associated with the amount of riparian and other natural vegetation in the surrounding 500m, (3) different groups of parasitoids were associated with unique types of natural vegetation, and (4) parasitism rates of sentinel cabbage aphid and cabbage looper pests were correlated with landscape vegetation features according to which parasitoids caused the mortality. Although individual species of parasitoids may thrive in landscapes that are predominantly short season crops, the robust associations found in this study across specialist and generalist parasitoids and different taxa (tachinid flies, ichneumon wasps, braconid wasps) shows that recent food safety practices targeting removal of natural vegetation around vegetable fields in an attempt to eliminate wildlife may harm natural enemy communities and reduce ecosystem services. We argue that enhancing biological diversity is a key goal for transforming agroecosystems for future productivity, sustainability and public health.