SPATIAL-DISTRIBUTION OF FALL POPULATIONS OF RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) IN WINTER-WHEAT

Current methods of characterizing spatial distributions of insects were applied to Russian wheat aphid, Diuraphis noxia (Mordvilko), data in winter wheat, Triticum aestivum L., plants sampled in the fall to derive information about the biology of this insect in the field and to develop sampling plans. The negative binomial fit well, but the k value was not constant, increasing rapidly and then remaining constant for mean densities >5 per plant Three dispersion indices indicated that the population was highly contagious initially but became less so as the population increased. Taylor's power law and Iwao's regression described similar relationships between the variance and the mean. Using Iwao's method, a sequential sampling plan for the mean density was developed using a decision threshold of 0.7 aphids per plant. An acceptable operating characteristic curve was obtained with an average sample number of <100 plants when the mean of aphids was near the threshold.