Impact of Host Plant Phenology on the Population Dynamics and Oviposition of Northern Corn Rootworms, Diabrotica barberi (Coleoptera: Chrysomelidae), in Field Corn

Abstract

The population dynamics and oviposition of adult Diabrotica barberi Smith and Lawrence were studied in relation to corn plant phenology from 1984 to 1986 near Ithaca, N.Y. In general, median times of adult emergence of both sexes were delayed, and the overall sex ratio of emerging beetles was progressively female-skewed in plots which flowered later. Males emerged earlier than females and, on a physiological time scale, had a shorter period of emergence; however, the length of the emergence period was not related to plant phenology in either sex. Both planting date and corn variety were shown to contribute to these general patterns. Delayed planting significantly delayed median emergence times of both sexes, reduced the number of beetles emerging, and increased the ratio of female to male emergence, but it did not influence the variance of emergence times. Variety manipulations had similar, but generally weaker, effects on emergence. Beetle flight activity was negatively correlated with the availability of corn flowers, and the ratio of females to males captured on sticky traps increased progressively from within plots to plot perimeters to areas surrounding the study site. Daily rates of adult mortality were significantly related to the availability of corn flowers and did not differ between the sexes. Changes in beetle population densities were closely synchronized with the availability of corn flowers, and seasonal population structure was dramatically influenced by the relative time of flowering. As plots flowered later, a greater percentage of the seasonal population were female and a greater percentage of these were mature. Changes in population structure affected the timing and magnitude of oviposition. Oviposition was completed sooner in plots that flowered earlier and, on a per beetle basis, total egg densities were higher in plots that flowered later.