Preliminary observations suggested that the parasitoids Metaphycus sp. nr. flavus and Metaphycus luteolus might use contact kairomones in order to recognize and accept as a host the brown soft scale Coccus hesperidum. Here we test this hypothesis by obtaining extracts of brown soft scales with different solvents and checking if the extracts are biologically active. Both species responded to extracts obtained with water and less to methanol extracts, with M. sp. nr. flavus responding more strongly than M. luteolus. These findings indicate that the kairomones used by these species to recognize their hosts are polar compounds, and they have a primary role in host selection and recognition behavior of these two species. Extraction protocols for preparing crude extracts and bioassay methods are described.