Monday, October 7, 2013

Sumac Flea Beetle


This colorful beetle was found on the Henning CA field trip, crawling on a forest plant.  It looks like it had a bad paint job on its elytra (wing cases) which has been chipping off.  This is a sumac flea beetle (Blepharida rhois) and it is supposed to look like that.  Actually in one life stage it  makes a stink when it covers itself with makeup, but we will get to that later.

Sumac Flea Beetle (Blepharida rhois) -wiki.bugwood.org
These little beetles measure a quarter of an inch in length.  They have enlarged hind femora (think thighs) with internal spring mechanisms that allows the insect to jump, the source of the "flea" in their name.

Sumac Flea Beetle Larvae- wiki.bugwood.org
The larvae are dull greenish-yellow and about ½ long. Their obligate host plant is one of the many species of sumac which vary depending on the location and climate.  They feed on the sumac leaves leaving a scattered hole pattern that looks like it had been hit by a load of fine birdshot from a shotgun.  After feeding into the early summer, they crawl into the soil to pupate, emerging as adults mid summer.  The adults continue to consume sumac leaves until they seek their winter shelter.

Now about that smelly makeup.  Like other beetles in the Blepharida flea beetle genus, the larvae of B. rhois retain their feces on their back rather than discarding it, a practice referred to as a "shield defense."  A study by Venci and Morton in Chemoecology showed that predatory ants attacked all the uncoated larvae and none of those bearing this shield.

Another species example of fecal shield defense  Zookeys
So was it the shield or the smell?  They next fed some larvae only lettuce which they again employed as a shield and the ants attacked them as though there was no shield.  It was obviously not the physical barrier or aesthetic concerns that put off the ants.  Further studies showed it was the chemicals they derived from their sumac host plant.
"The shield defense was a mixture of three fatty acids, a suite of tannins, their metabolites and phytol. All shield compounds or their precursors were obtained entirely from the host plant. Pure standards of shield compounds were found to be deterrent when assayed. This is one of the first instances of an insect using a mixture of primary and secondary substances for defense against predators."  Shield defense paper
Everything in nature is eventually recycled.  In this case the sumac flea beetle has gone beyond the recycling trend, practicing what is called in current terminology "repurposing." 

*  More information is at Bugwood.org.
This is one of a series on finds on the Master Naturalist training field trip.  More pictures from the  field trip are at Finds from the Field 

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