Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 1999
Publication Date: May 1, 2000
Interpretive Summary: Wheat, barley, and sorghum are some of the most important crops grown in the United States. Aphids are key pests of these crops, causing annual losses in excess of $250 million. Insecticides have traditionally been used to control them. However, low profit margins make their use economically prohibitive; environmental contamination and development of insecticide- resistant pests are also concerns. Many species of parasitic and predatory insects can destroy large numbers of aphids, but their importance is difficult to assess because of a lack of monitoring tools. This research was designed to create specific monitoring tools for two species of parasitic microwasps that have been released into wheat fields to control aphids. We discovered unique portions of the genetic material, DNA, that distinguish these two species from three other microwasp species and two major aphid pest species. Using techniques to detect the DNA, we can also determine whether an aphid has been parasitized by a wasp within 24 hours of the wasp having laid her eggs within the aphid. These tools enable us to determine what proportion of an aphid population has been parasitized by each microwasp species, and thereby determine the importance of each one in controlling aphid populations. This technology is mostly of interest to scientists right now, but in the future may be useful to crop consultants and growers.
Technical Abstract: To monitor aphid parasitism by Aphelinus hordei (Kurdjumov) and Aphidius colemani Viereck, we developed specific ribosomal DNA markers to distinguish them from several other cereal aphid parasitoid species and two important host species, the Russian wheat aphid, Diuraphis noxia (Mordvilko), and the greenbug, Schizaphis graminum (Rondani). Ribosomal DNA Asequences for the internal transcribed spacer 2 (ITS2) were first cloned and sequenced from Aphelinus hordei, A. albipodus Hayat & Fatima, A. asychis Walker, A. varipes (Foerster), Aphidius colemani, D. noxia, and S. graminum. We designed specific primers based on the ITS2 sequences. Polymerase chain reaction (PCR) amplification of wasp and aphid DNA using these primers, followed by agarose gel electrophoresis, successfully distinguishes A. hordei and A. colemani from all three other Aphelinus species and two aphid species. A 411 bp nucleotide fragment and a 571 bp fragment were amplified only from A. hordei and from A. colemani, respectively, and no such fragments were amplified from any other wasp species or aphids. DNA could be detected at a level as low as 10*-3 adult wasp equivalent for A. hordei and 5 x 10*-4 adult wasp equivalent for A. colemani. DNA of both species was detectable in parasitized D. noxia 24 h following initial contact with adult parasitoid pairs.