Weight gain of first-instar monarch larvae feeding on milkweeds placed at 1, 3, 5, and 10 m inside (negative value) and outside the field edge of event-176 field corn in Maryland. Means ± SE are based on separate bioassays conducted on days 3, 6, 9, and 14 of anthesis. Within each graph, columns with the same letters are not significantly different (P < 0.05; Tukey's test).