Entomologia Experimentalis et Applicata 99: 1–12, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 1 Development and evaluation of an enzyme-linked immunosorbent assay to detect Pieris rapae remains in guts of arthropod predators M. A. Schmaedick 1,3 , K. S. Ling 2,4 , D. Gonsalves 2 & A. M. Shelton 1 1 Department of Entomology, NYSAES, Cornell University, Geneva, NY 14456, USA; 2 Department of Plant Pathol- ogy, NYSAES, Cornell University, Geneva, NY 14456, USA; 3 Current address: Land Grant Program, American Samoa Community College, PO Box 5319, Pago Pago, AS 96799, USA; 4 Current address: AgriVitis, Inc., 2191 San Juan-Hollister Road, San Juan Bautista, CA 95045, USA Accepted: August 31, 2000 Key words: ELISA, polyclonal antisera, sensitivity, specificity, Pieris rapae, predation Abstract An enzyme-linked immunosorbent assay (ELISA) was developed to detect remains of Pieris rapae L. (Lepidoptera: Pieridae) immature stages in the guts of field collected arthropod predators. The assay can be used to help ascertain the relative importance of arthropod predator species in suppressing P. rapae in cabbage, Brassica oleracea var. capitata L. The ELISA is sensitive to all immature stages of P. rapae, although first and fifth instars can be detected more readily than eggs or pupae and third instars showed intermediate detectability. Assays on whole body homogenates of predators readily detected predation on P. rapae first instars by all seven of the predator species tested, although response generally declined with increasing predator size. Together the results show that the P. rapae ELISA possesses a sufficiently high level of sensitivity and specificity to be a useful tool in helping to elucidate the roles of arthropod predator species in reducing populations of P. rapae in cabbage. Introduction Immunological assays to detect prey remains in the guts of predators collected from the field are a use- ful tool to help researchers identify important trophic connections within an ecosystem (Powell et al., 1996). Once developed, these assays can serve as an efficient and sensitive means to test large numbers of field col- lected predators for evidence of feeding on a specific prey item, such as a key agricultural pest. However, immunoassays must be carefully assessed before they can be used in ecological studies (Boreham & Ohiagu, 1978; Sopp et al., 1992; Kidd & Jervis, 1996; Sun- derland, 1996). Critical aspects that must be evaluated include sensitivity and specificity, and effectiveness in detecting predation by different species. This paper documents these attributes for an immunoassay that we developed for a key pest of cabbages (Brassica oleracea variety capitata L.) in New York State. The target of our immunoassay, the imported cab- bageworm, Pieris rapae L. (Lepidoptera: Pieridae), is a serious pest of cabbages and other crucifer crops in North America and many other parts of the world. While research elsewhere (including some using im- munological assays) has shown that predatory arthro- pods can cause high levels of mortality in P. rapae populations (Dempster, 1967; Parker, 1970; Ashby, 1974; Hasui, 1977; Jones et al., 1987), until recently the impact of predators has not been evaluated in New York. The objective of this study was thus to develop and characterize an enzyme-linked immunosorbent as- say (ELISA) to help identify important predators of P. rapae on cabbages in New York State. In particular, five aspects of the immunoassay were addressed: (1) the assay’s sensitivity to first instar P. rapae, the stage which appears most susceptible to predation (Demp- ster, 1967; Ashby, 1974; Schmaedick & Shelton, 1999); (2) differences in sensitivity to the different immature stages of P. rapae; (3) specificity (i.e., the levels of cross-reactions to other species); (4) ability to detect predation by seven predator species; and (5)