Effects of Corn Phenology on Spatial Distribution and Population Estimation of Adult Northern Corn Rootworms (Coleoptera: Chrysomelidae)

Abstract

The spatial distribution of adult Diabrotica longicornis barberi Smith and Lawrence in a Quebec cornfield varied with host phenology. The initial distribution in the second half of July was “contagious”; distribution was random during the first 2 weeks of August when the crop was in full bloom. Distribution was again “contagious” when most of the corn silks dried up after mid-August. Concurrent with changes in beetle distribution, numbers of corn plants necessary for population estimation with a particular precision level changed as the season progressed. During the second week of August when the population peaked, approximately 40% of the beetles were found inside the axils of leaves, and from 40 to 50% on silks and ear-tips. During this period, beetle counts on 40 randomly selected plants give a reasonably accurate estimate of the field population, with a standard error of less than 10% of the mean.