Tuesday, September 22, 2015

Milkweed Leaf Beetle

Southern Milkweed Leaf Beetle - Labidomera clivicollis - REK
While collecting wildflower seeds for the WOLF school, Barb spotted Monarch caterpillars on the milkweed planted nearby.  When the students came out to see them they discovered a variety of orange and black insects including these colorful beetles which look like lady beetles with a bad paint job.  They are actually Southern Milkweed Leaf Beetles, Labidomera clivicollis.

Adults and larvae feed exclusively on the milkweed family, Asclepiadaceae.  Milkweed contains a toxin that they will consume, serving to partially protect them from predators.  Even these beetles can take only so much toxin, so they will frequently cut the veins to reduce the sticky latex sap flow to the outer leaf they intend to feed on.

After mating, the females lay eggs on the underside of the milkweed leaves, attaching them with their own brand of glue.  The larvae will feed on the leaves, progressing through 4 instars before dropping to the ground to pupate.  The adults overwinter among the leaf litter before meeting at the nearest milkweed to mate in the spring.

Color variations of L. clivicollis - Photo by  Mike Quinn CC
L. clivicollis can display a wide variation in color shades of the basic orange and black.  A variety of insects with this coloration form what is called the "milkweed mimicry complex".  All of these species have evolved mechanisms to avoid the toxic effects of cardenolides while retaining them in their body fluids for protection.  The most famous example is the Monarch butterfly but the other species below also have developed this trick of metabolism.  
The shared warning coloration is called Müllerian mimicry, announcing that "I will make you sick like the others colored like me."  Examples include the Small and Large Milkweed Bugs, Milkweed Tussock Moth, Milkweed Assassin Bug and even the Milkweed Aphid.   A few other insects like the Viceroy butterfly benefit from the coloration without the toxins, called Batesian mimicry.

Milkweed Assassin Bug - peppersnack
Milkweed Beetle - Tetraopes tetraopthalmia -REK

Large Milkweed Bug - REK

Small Milkweed Bug - REK

Ready to from chrysalis
Milkweed Aphids -  REK

None of these cause significant competition for the Monarch caterpillar above whose main challenge is finding milkweed in the face of our monoculture agriculture which tends to crowd out native species.  The plants at the WOLF school made its coming transition possible.

You can do your part by planting milkweed and enjoying this colorful food web just outside your door.

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