A comparative study on the efficacy of a pest-specific and prey-marking enzyme-linked immunosorbent assay for detection of predation

The efficacy of two different antigen-antibody combinations to detect predation on eggs of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) was compared. The first method was an indirect enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody-based gut content analysis that detects H. armigera egg protein. The second method was a sandwich ELISA that detects an exotic protein [rabbit immunoglobulin G (IgG)] applied as an external marker to H. armigera eggs. The target predators were the predatory beetles Dicranolaius bellulus (Guerin-Meneville) (Coleoptera: Melyridae) and Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). Beetles were fed with H. armigera eggs that had been marked with rabbit IgG and then held at various intervals after prey consumption. Each individual beetle was then assayed by both ELISA techniques to identify the prey remains in their guts. The two ELISA methods were further tested on field-collected predators. Specifically, protein-marked egg masses were strategically placed in a cotton field. Then, predators from surrounding cotton plants were collected at various time intervals after the marked eggs were exposed and assayed by both ELISAs to detect the frequency of predation on the marked eggs. The rabbit IgG-specific sandwich ELISA had a higher detection rate than the H. armigera-specific indirect ELISA under controlled and field conditions for both predator species. Moreover, a greater proportion of field-collected D. bellulus tested positive for predation than H. variegata. The advantages and disadvantages of using prey-marking ELISAs instead of pest-specific ELISA assays are discussed.