Polymerase chain reaction techniques for distinguishing three species and two strains of Aphelinus (Hymenoptera: Aphelinidae) from Diuraphis noxia and Schizaphis graminum (Homoptera: Aphididae)

Ribosomal DNA sequences for the internal transcribed spacer 2 (ITS2) were cloned and sequenced from Aphelinus albipodus Hayat & Fatima, A varipes (Foerster),and 2 strains of A. asychis Walker, all endoparasitoids that have been released against the Russian wheat al,hid, Diuraphis noxia (Mordvilko). The polymerase chain reaction (PCR) using primers designed on the basis of these rDNA sequences, followed by agarose gel electrophoresis, successfully distinguishes all 4 Aphelinus populations from each other and from the Russian wheat aphid and another economically important cereal aphid, the greenbug, Schizaphis graminum (Rondani). Two additional strains of A. asychis and 4 postrelease populations of A. albipodus are also correctly identified to species with these primers. An additional strain of A. varipes was not separable from A. albipodus, but on microscopic analysis it proved to be morphologically anomalous. Using this technique, A. asychis DNA is detectable in a parasitized Russian wheat aphid 24 h after parasitization. The sensitivity is 10(-3) adult wasp DNA equivalent.