|Brewer, Michael - UNIV WYOMING|
|Struttmann, J - UNIV WYOMING|
|Oswald, C - UNIV WYOMING|
Submitted to: Thomas Say Publications in Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 1997
Publication Date: N/A
Interpretive Summary: Russian wheat aphid, Diuraphis noxia (Mordvilko), is a devastating pest on barley in seventeen western states. Because of its ability to keep leaves from unrolling, thus forming a protective barrier to contact insecticides, systemic insecticides must be used to control RWA. These insecticides pose a threat to the environment and contaminate barley endproducts. Host plant resistance combined with biological control would be the preferred approac to control RWA. Resistant lines have been identified with varying levels of resistance as seedlings in the greenhouse. How these lines perform in the field, as well as their interaction with four natural parasitoids, were the objectives of this study. Agronomic data are reported elsewhere. Parasitoid abundance did not appear to be affected by variance in the level of resistance in the different lines. Any of these lines found to perform the best agronomically should be effective with natural biological parasitoids. .These results indicate that the future release of RWA-resistant cultivars will fit nicely into a complete integrated pest management system for natural control of RWA in barley. These results are important to farmers, state breeders, and the barley industry as a whole. Farmers now can look forward to reduced pesticide use and high yields even in the presence of RWA. State breeders can work with RWA-resistant lines without fear of reduced yields or a negative effect on natural biological control agents. The barley industry, both feed and malting and brewing, can look forward to barley endproducts free from insecticide contamination.
Technical Abstract: Plant response (e.g., chlorosis and leaf rolling), density of Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), and relative abundance of parasitoids (Hymenoptera: Braconidae and Aphelinidae) were measured on twenty lines of field-grown barley, Hordeum vulgare L., varying from highly resistant to highly susceptible to Russian wheat aphid. Barley lines were challenged with Russian wheat aphid throughout plant development. Plant and insect responses were compared with results from greenhouse tests that assessed seedling resistance. Ratings of resistance based on chlorosis from previous greenhouse seedling tests predicted plant susceptibility to Russian wheat aphid in later plant growth stages as measured by chlorosis and leaf curling, 67 days after planting. Russian wheat aphid were found on all barley lines, and densitites increased as seedling plant susceptibility increased, resulting in densities as high as 70 aphids per tiller. Parasitoids detected were Diaeretiella rapae McIntos (Hymenoptera: Braconidae), Aphelinus albipodus Hayat and Fatima, A. varipes (Foerster), and A. asychis (Walker) (Hymenoptera: Aphelinidae). Weighted parasitoid abundance (count of aphid mummies per tiller divided by the count of live Russian wheat aphids per tiller) for D. rapae averaged up to 0.75:1 among the barley lines. For the aphelinids, weighted parasitoid abundance was typically lower, but in one late-season occurrence a ratio of 6:1 was detected (in this instance parasitoids were released around the plot). In general, five times as many A. albipodus were detected as A. asychis, even though they were released in equal numbers. Weighted parasitoid abundance varied less among the barley lines than did plant damage and aphid densities.