Release and recovery in South Africa of the exotic aphid parasitoid Aphelinus hordei verified by the polymerase chain reaction

The exotic aphid parasitoid Aphelinus hordei Kurdjumov (Hymenoptera: Aphelinidae) was released at five Russian wheat aphid [Diuraphis noxia (Mordvilko)] infested wheat fields in the eastern parts of the Free State Province of South Africa during the 1998 and 1999 growing seasons. Except for differences in the setae on the ventral side of the forewings, this species is very similar in colour and structure to A. varipes (Foerster) and A. albipodus Hayat & Fatima, which also parasitise D. noxia. It is therefore difficult to distinguish between them, and to determine their establishment. Therefore a polymerase chain reaction, using specific primers for both ITS2 and mitochondrial 16s DNA sequences of the three parasitoids, followed by HinfI restriction endonuclease digestion and agarose gel electrophoresis, was tested to distinguish between them. Parasitoid recoveries were made at the release sites within weeks after they were released. Putative individuals of A. hordei were also collected during 1999 and 2000 on D. noxia in Lesotho, which is situated on the eastern border of the Free State Province. The procedure separated the three Aphelinus spp. reliably. Between 94 and 100% of the individuals recovered during the two field seasons were identified as being A. hordei, thus verifying recovery of this exotic aphid parasitoid in South Africa.