Corn pollen deposition on milkweeds in and near cornfields

Authors

John M. Pleasants, Iowa State UniversityFollow
Richard L. Hellmich, Iowa State UniversityFollow
Galen P. Dively, University of Maryland, College Park, MD
Mark K. Sears, University of Guelph, Guelph, ON, Canada
Diane E. Stanley-Horn, University of Guelph, Guelph, ON, Canada
Heather R. Mattila, University of Guelph, Guelph, ON, Canada
John E. Foster, University of Nebraska-LincolnFollow
Peter Clark, University of Nebraska-LincolnFollow
Gretchen D. Jones, USDA-ARS

Document Type

Article

Date of this Version

10-9-2001

Citation

PNAS, October 9, 2001, vol. 98, no. 21, pp. 11919–11924.

Comments

Copyright 2001 the authors. Used by permission.

Abstract

The density of corn pollen on leaves of milkweed plants inside and outside of cornfields was measured in several studies from different localities. The purpose was to obtain a representative picture of naturally occurring pollen densities to provide a perspective for laboratory and field studies of monarch larvae feeding on milkweed leaves with Bt corn pollen. Pollen density was highest (average 170.6 grains per cm²) inside the cornfield and was progressively lower from the field edge outward, falling to 14.2 grains per cm² at 2 m. Inside the cornfield, and for each distance from the field edge, a frequency distribution is presented showing the proportion of leaf samples with different pollen densities. Inside cornfields, 95% of leaf samples had pollen densities below 600 grains per cm² and the highest pollen density observed was 1400 grains per cm², which occurred in a study with a rainless anthesis period. All other studies had rainfall events during the anthesis period. A single rain event can remove 54–86% of the pollen on leaves. Leaves on the upper portion of milkweed plants, where young monarch larvae tend to feed, had only 30–50% of the pollen density levels of middle leaves.