EFFECTS OF HOST PLANT ON THE BETWEEN-PLANT SPATIAL-DISTRIBUTION OF THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE)

The spatial distribution of the Russian wheat aphid, Diuraphis noxia (Mordvilko), on 'Stephens' wheat and 'Border' oats was evaluated using geostatistics. Geostatistics uses spatial variation to determine the degree and type of spatial dependence of spatially related data. These analyses revealed unique spatial distributions of Russian wheat aphids on wheat and oats, which varied as the population developed and dispersed among the plants. On 'Stephens' wheat, Russian wheat aphid dispersal from the release site was delayed, and when aphids dispersed, they moved a greater distance than those on 'Border' oats. When placed on 'Border' oats, Russian wheat aphids dispersed within 3 d of the initial infestation and continued to disperse throughout the 21-d sampling period. The Russian wheat aphid distributions estimated by negative binomial K, Lloyd's mean crowding index, Iwao's patchiness regression, and Taylors' power law were compared with the geostatistical analysis and found to have a similar interpretation of distribution only 50-80% of the time under the laboratory conditions of this research. These differences reveal the limited value of these dispersion indices for evaluating spatial distribution.