Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 1999
Publication Date: December 1, 1999
Citation: Brewer, M.J., Mornhinweg, D.W., Huzurbazar, S. 1999. Compatibility of insect management strategies: Diuraphis noxia abundance on susceptible and resistant barley in the presence of parasitoids. Biocontrol. 43:479-491.
Interpretive Summary: Russian wheat aphid (RWA) is a devastating pest of barley in the intermountain regions of the western United States. Barley germplasm lines with varying degrees of RWA resistance have been developed in the greenhouse by evaluating seedlings from the National Small Grains Collection at Aberdeen, ID. An ideal RWA control program would utilize not only plant resistance but also include biological control by natural parasites and predators of the RWA. RWA-resistant lines do not have the same reaction to RWA as do susceptible varieties. RWA survive in low numbers on these resistant lines without damaging the seedlings, whereas RWA survive in high numbers and severely damage seedlings of susceptible varieties, causing leaves to roll, streak, and turn yellow. A field test was needed to see if the plant response of resistant lines would support the natural parasitoid populations and not interfere with the control of RWA by these parasites. Resistant lines were grown in the field where parasites naturally occurred. RWA were artificially applied to the field and observations made on the compatibility of the new RWA-resistant lines and naturally occurring parasitoids. The parasitoids observed in this study were native to Wyoming and had no problem parasitizing RWA on the resistant lines as well as on the susceptible lines. The use of future RWA-resistant barley varieties by farmers should not hinder the ability of naturally occurring parasites to also play a role in the RWA control.
Russian wheat aphid, Diuraphis noxia, and parasitoid abundance were monitored on field-grown barley, Hordeum vulgare L., varying in D. noxia susceptibility, to address the applicability of previous laboratory assessments of barley seedling resistance and parasitoid compatibility. Study sites were representative of the barley production region of the High hPlains in the western USA, where D. noxia and its parasitoids occur. D. noxia abundance on resistant barley lines, characterized as partially tolerant and antibiotic to the aphid, was lower than on more susceptible lines. Parasitism by Diaeretiella rapae, Aphelinus albipodus, and A. asychis differed in seasonal occurrence and abundance. D. rapae mummies occurred sooner than aphelinid mummies, and there were larger increases in aphelinid mummies than in D. rapae mummies during seed head development. But in regard to plant resistance, parasitoid abundance, relative to D. noxia abundance, was similar on resistant and susceptible barley lines. Based on the susceptibility of commercial barley to D. noxia, the seasonal abundance of D. noxia and its parasitoids, and the compatibility of resistant barley and D. noxia parasitoids, the use of resistant barley in areas of parasitoid establishment is justified.