Unknown Potato Beetle Larva

Red caterpillar?
Location:  Payson, Arizona
September 5, 2010 11:20 pm
We found this bug Payson Arizona, mogollon rim area. It is very interesting with the red color, black spots and black collar. We would like to know more about this bug.
Signature:  LHastings

Unknown Leaf Beetle Larva

Dear LHastings,
This is the larva of a Leaf Beetle in the family Chrysomelidae (See BugGuide) and we are nearly certain it is in the subfamily Chrysomelinae (See BugGuide), but after that we draw a bit of a blank.  There is a strong resemblance to the larva of the Colorado Potato Beetle, but photos we have seen show a black head on the larva of the Colorado Potato Beetle unlike the red head in your photo.  Additionally, like many leaf beetles, the Colorado Potato Beetle is quite selective about its food plant, and it feeds on the leaves of plants in the potato family including nightshade.  Your larva appears to be feeding on grass.  There is a closer resemblance to the larva of the Swamp Milkweed Beetle, but again there are inconsistencies with both the food plant and the range of the Swamp Milkweed Beetles which according to BugGuide are found east of the Rocky Mountains.  An additional problem is that it is generally far easier to identify an adult insect than a larva.  We will contact Eric Eaton who is familiar with the insects of Arizona to see if he can provide any additional information.

Eric Eaton Responds
Hi, Daniel:
I’d say that more than likely it is in the genus Leptinotarsa, which includes the infamous “Colorado Potato Beetle,” but also several other species here in Arizona.  Always helps to know what plant it was feeding on.

Thank you for looking into this for me.  The bug is not on the grass.  It has pretty much finished eating a plant, and the stalk is behind the grass.  I am attaching a photo of what it is feeding on.  This may help.
Thank you for taking the time to look into this.

Probably Leptinotarsa Larva

Thanks for providing a better photo of the food plant Laura.  It appears to be feeding on a member of the nightshade family.  Your new photo and Eric Eaton’s comment have convinced us that this is a Potato Beetle in the genus Leptinotarsa, but not the Colorado Potato Beetle whose larva has two rows of black dots on each side (see BugGuide). As Eric Eaton has indicated, there are other members of the genus found in Arizona, and BugGuide has images of two species of adults, but alas, there are no photos of the larvae.  The first is Leptinotarsa haldemani, Haldeman’s Green Potato Beetle (see BugGuide) and the second is Leptinotarsa rubiginosa, the Reddish Potato Beetle (see BugGuide).  We have also had no luck in finding any photos online of the larvae of those species.  We hope you are content with a genus identification.

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