The last generation of monarchs migrates to Mexico in the fall. These migratory adults do not mature sexually until spring--about the time they leave their winter refuges in Mexico. This allows the migratory monarchs to build more muscles and fat deposits for migration--without wasting energy to grow mature reproductive organs. Reproductive monarchs live two to six weeks; they mature sexually 4-5 days after emerging from the chrysalid. The migratory ones live for 9 months.
This creates a challenge for our program. If the butterflies we choose as breeders are migratory adults--they won't mate and lay eggs! We want to choose "reproductive adults" to breed. The problem is, we can't tell them apart, and don't know when the emerging butterflies switch over from "reproductive" to "migratory" adults. It's suspected the cues that influence developing caterpillars to become migratory are decreasing daylength, declining temperatures, and decreasing food quality.
Teachers want eggs in the classrooms around Sept. 1, but the last eggs are laid in the wild around the end of August. So, it would be reasonable to conclude that any females you capture at the end of August, to use as breeders, will be migratory. No eggs that way!
The alternative I've used for years is to find eggs and start raising caterpillars in late July. One can assume that--raised indoors with artificial light and good quality food, the resulting monarchs will be reproductive. Over the years, my success in producing reproductives in late August indicates these assumptions are correct.
Starting in July, it takes about 30 days to produce a butterfly, then 4-5 days to become sexually mature, then more time to mate and produce eggs. I could save a lot of work and start later in August if I could capture wild reproductive females who have mated, then tame them so they produce eggs in captivity. This year, I captured three wild females on August 15. They tamed and learned to feed on my "artificial flowers" in just a few days. All three of them turned out to be reproductives that laid eggs.
One warm, sunny day in late August, four laying females produced 290 eggs in one day.>
Now on Sept. 5 I'm trying to mate females and males that were captured after August 15, trying to find when the latest reproductive females can be found in the wild.
Another refinement is to find out how many laying females are needed to supply all my schools. There are things I can't control. Cool or rainy weather slows or shuts down laying. Some of the laying females can become injured or just worn out from old age--especially if they are captured in the wild. I had to let one laying female go because she was infected with the OE parasite. Last year, one of my two tents was ripped open at night by a raccoon, who ate all of the monarchs. They were surplus males I was about the release, so it didn't affect egg production for schools.
Since I serve so many schools, it's really important that I can produce eggs reliably. Each year, I try to refine the process so it's less work but more reliable.