Do perennial habitat fragments support greater parasitoid diversity and pest regulation in ephemeral crops?

Background/Question/Methods

To examine the role of native perennial vegetation in agricultural landscapes in providing critical habitat for supporting ecosystem services and sustainable agriculture, we sampled mobile arthropods in short-cycle, organically-managed crops in California. These agroecosystems are notoriously challenging for achieving conservation biological control because frequent disturbance precludes the establishment of resident communities of natural enemies of pests. Tachinidae, a diverse and ubiquitous family of parasitoid flies, were sampled for three seasons in 35 organic farm fields situated within a mosaic of agricultural and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500m and 1500m, including grasslands, chaparral, oak woodlands, and coniferous forests.

Results/Conclusions

The abundance and species richness of tachinid flies captured in field crops in spring and summer were positively associated with the cover of semi-wild perennial vegetation, and the species richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants in these organic vegetable fields was negatively associated with annual cropland cover. We discuss the importance of maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids that provide ecosystem services in annual and short-cycle crop fields, and distinctions between fragments dominated by native versus introduced plants.