Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 27, 1997
Publication Date: N/A
Interpretive Summary: Russian wheat aphid (RWA), a new pest to the United States, causes great reductions in barley grain yield in years when aphid populations are present. Leaves of susceptible cultivars streak and roll when infested with RWA, which provides the aphids with a protected niche on the plant to feed and reproduce. STARS-9301B is a tolerant barley germplasm line whose leaves sdo not streak or roll with RWA infestation and which will support exposed aphids but at lower populations. Several biological control insects successfully parasitize RWA in the rolled up leaves of susceptible cultivars, but their ability to parasitize RWA on the flat leaves of resistant barleys was yet unknown, putting in question their compatibility with resistant cultivars in an integrated pest management (IPM) program. Both parasitoids were able to successfully parasitize RWA on STARS-9301B, indicating the compatibility of biological control and resistant cultivars in an IPM system for control of RWA. These results are very encouraging to researchers and farmers who are working toward natural control of RWA.
Russian wheat aphid, Diuraphis noxia (Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid by Aphelinus albipodus Hayat & Fatima and Diaeretiella rapae McIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the larger D. rapae was more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism by A. albipodus did not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism by D. rapae was greater than A. albipodus. These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.