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Archive for September 7, 2011

Some Monarchs Outwit Milkweed

We think of monarch larvae as being impervious to the  ills of milkweed, but they are very vulnerable when it comes to the sticky latex in the sap of their host plant.  The mandibles of young monarch caterpillars are often glued together by this latex, preventing them from eating.  Research shows that about 30 percent of monarch larval loss results from miring  in this glue-like substance.  One strategy young larvae use is to chew a near circle in a milkweed leaf, blocking the flow of latex to the enclosed surface area, which they then eat.  If a monarch survives the first few stages, or instars, of its larval life, it uses yet another strategy to circumvent the latex.  Older, larger larvae often cut through the midvein of a leaf they wish to consume, which dams the latex flow to the entire leaf beyond the cut.  Look for limp leaves as you peruse a milkweed patch.  If you find one, you may be rewarded with the nearby presence of a monarch caterpillar.