The past month I have had the opportunity to witness first hand how well the wild monarch caterpillars are surviving this year even on dusty, noisy and sprayed roadsides.
On June 28 I noticed a baby 2nd instar caterpillar on a roadside speciosa milkweed milkweed about 50 miles east of Sacramento in the Sierra foothills. Then I watched it grow into a large caterpillar that formed it's chrysalis on the milkweed plant around July 12. Then yesturday, July 27 the butterfly emerged. Here is a photo of the original baby caterpillar and video of the butterfly just
minutes after it had emerged: http://www.learner.org/cgi-bin/jnorth/j ... 1311886164
The ground where this milkweed was growing was sprayed with a roadside herbicide (probably Transline herbicide) in April: http://i959.photobucket.com/albums/ae78/18R-C/spray.jpg
http://i959.photobucket.com/albums/ae78 ... sprayb.jpg But the milkweed had not emerged from the ground at the time of the spraying so the plants were not seriously harmed and the spray had no effect on subsequent caterpillar or butterfly health.
This experience demonstrates that roadside herbicide spraying can be compatible with milkweed and monarch health if conducted in the late winter or early spring before the milkweed has emerged from the ground.