A plate enzyme-linked immunosorbent assay (ELISA) using the biotinavidin system was developed for identifying larvae of the spotted tentiform leafminer,Phyllonorycter blancardella(F.), parasitized byPholetesor ornigis(Weed). Host larvae were chemically extracted, without trituration, directly in antibody-coated ELISA plate wells containing sodium dodecyl sulfate, mercaptoethanol, and EDTA buffered with TRIS. Detergents were used in the extraction buffer to prevent loss of serological activity and to reduce nonspecific reactions. The assay was accurate using fresh or frozen specimens. The correlation between parasitoid size and ELISA value was highly significant down to a parasitoid length of ≍0.34mm. Parasitoid eggs or early-stage larvae were not detectable with antiserum prepared to cocoons.