Monday, June 13, 2016

Tortoise Beetles

On the MPF Bioblitz, Christine presented me with the challenge above.  They appeared to be a beetle larvae, but which ones and what is with the black flags?  After thumbing through the usual sources, I sent it to Bi-State Bugs.  Helen Wilbers pointed me in the right direction with Tortoise Beetle larvae, famed for collecting their fecal material on their backs as a shield.  She suggested Physonota unipunctata as a likely suspect. 

   P. helianthi - Bugguide -Tom Murray CC
Bugguide showed pictures of P. unipunctata which were a good match but stressed the similarity to the Sunflower Tortoise Beetle (STB), Physonota helianthi, whose larval host plants are members of the aster family, Asteraceae.  James Trager meanwhile suggested that the leaf in the picture looked like Berlandiera texana (an Asteraceae) that we had been seeing on the prairie.  The leaf is a perfect fit so I am settling on a STB until others vote me down.

Sunflower Tortoise Beetle - Tom Murray
Mature beetle - Kerry Yurewicz
The STB and its larvae feed on the underside of sunflower (Helianthus) leaves.  The beetle goes through some interesting color changes once it emerges.  It starts a dingy white, then becomes black and white for three weeks.  Finally it reaches its final adult stage as a bright metallic green.  The progression continues after death to a pale yellow to brownish gray.

Tortoise Beetle larvae have an interesting defense as described in Bugguide. 
"The larvae carry their cast skins and fecal material attached to spines arising from the posterior end of their body, a structure called an "anal fork." The anal fork is movable, and is used to hold the debris over the back of the body, forming a "shield" which deters predation."
View of head with black anal forks naked - REK
Fecal shield on an "anal fork"
This type of shield defense is not unique to tortoise beetles' larvae.  Lacewing larvae decorate the hairs on their backs with trash including remnants of their aphid prey.  One species of West African assassin bug carries its ant victims on its back to ward off spiders.

More on fecal shields on this blog.

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