Temporal and spatial overlap between monarch larvae and corn pollen.
To assess the likelihood that monarch larvae will be exposed to Bacillus thuringiensis (Bt) pollen, we studied milkweed and monarch densities in habitats which comprise much of the land available to breeding monarchs, e.g., cornfields, cornfield edges, other agricultural fields, and nonagricultural areas, in four regions of the monarch breeding range. We found that monarchs use milkweed in cornfields throughout their breeding season, and that per plant densities are as high or higher in agricultural habitats as in nonagricultural habitats. As a result of the prevalence of agricultural land, most of the monarchs produced in the upper Midwest are likely to originate in cornfields or other agricultural habitats. There was a greater temporal overlap between susceptible monarchs and corn anthesis in the northern than the southern part of the summer breeding range, because of earlier pollen shed in the south. The importance of agricultural habitats to monarch production suggests that, regardless of the impact of genetically modified crops, agricultural practices such as weed control and foliar insecticide use could have large impacts on monarch populations.
Oberhauser
K S
KS
University of Minnesota, Department of Ecology, Evolution and Behavior, 1987 Upper Buford Circle, St. Paul, MN 55108, USA. oberh001@tc.umn.edu
Prysby
M D
MD
Mattila
H R
HR
Stanley-Horn
D E
DE
Sears
M K
MK
Dively
G
G
Olson
E
E
Pleasants
J M
JM
Lam
W K
WK
Hellmich
R L
RL
D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002080:Butterflies; D004731:Endotoxins; D006460:Hemolysin Proteins; D007814:Larva; D019684:Magnoliopsida; D010063:Ovum; D010572:Pest Control, Biological / Q000379:methods; D030821:Plants, Genetically Modified; D011058:Pollen; D003313:Zea mays
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis