FUNGAL ENTOMOPATHOGEN EFFECT ON NUMBERS AND SPATIAL PATTERNS OF THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) ON PREFERRED AND NONPREFERRED HOST PLANTS

Effects of plant-host type, either wheat, Triticum aestivum L., or oat , Avena sativa L., and the fungal entomopathogen Beauveria bassiana (B alsamo) Vuillemin, on numerical and spatial distributions of Russian w heat aphid, Diuraphis noxia Kurdyumov, populations were investigated. Untreated adult aphids or aphids inoculated with conidial suspensions of the pathogen were released onto the center seedlings of an 81-seedl ing grid in a cage. After 17 d, the numbers of live adults, live nymph s, and sporulating cadavers were recorded for each plant, along with p lant height and dry weight. Aphid populations were consistently lower on oat than on wheat, and lower in B, bassiana treatments. Spatial sta tistics (geostatistics) were used to compare patterns of aphid distrib ution on plants. On wheat without the pathogen present, adult aphid po pulations were highest in approximately concentric rings near the oute rmost plants in grids. Addition of B, bassiana to the system reduced t he amount of variation caused by spatial orientation, thereby changing the spatial distribution of aphid populations. On oat, aphid populati ons generally were highest near the center of the grid, but addition o f the pathogen changed the spatial structure of the aphid population. Results suggest that aphid movement behavior, which is intimately link ed to host-plant quality, is an important determinant of epizootic pro liferation. Elucidation of these relationships may eventually lead to a synergistic use of microbial control agents and host-plant resistanc e in pest management strategies.