Identification of predator-prey relationships between coccinellids and Saissetia oleae (Hemiptera: Coccidae), in olive groves, using an enzyme-linked immunosorbent assay

A polyclonal antiserum (AS) was developed and characterized for the detection of immature stages of the black-scale, Saissetia oleae, in whole body homogenized field-collected coccinellid species, using an indirect enzyme-linked immunosorbent assay (ELISA). The indirect ELISA showed to be sensitive to the S. oleae AS, detecting a protein content between 0.118 and 0.0374 mu g mL(-1). The specificity of the ELISA was tested by assaying a range of sympatric predators and alternative preys with the S. oleae AS. Coccinellid larvae obtained the highest cross-reaction and a positive-negative threshold was established at 0.674 mu g mL(-1) protein. A total of 1,322 coccinellids were field-collected in three olive groves located in Tras-os-Montes (northeast of Portugal) by the beating technique and were analyzed to detect S. oleae proteins in their guts. Field-collected coccinellids which attained a S. oleae protein concentration equivalent higher than the threshold were considered as a positive reaction. In the overall collected coccinellids, 21.2% reacted positively with the S. oleae AS. Chilocorus bipustulatus and coccinellid larvae obtained the highest percentages of positives with 43.4 and 40.8%, respectively. The greatest frequency of positive responses occurred at the beginning of July, mid-August, and mid-October coinciding with the occurrence of the first, second and third instar nymphs of S. oleae, respectively. Thus, in this study, the role of coccinellids as natural control agents of S. oleae was highlighted by the number of individuals and species that tested positive for S. oleae AS.