Leaf-mining Weevils

On my recent road trip I got a chance to photograph several insect signs that I had described in my book but had never seen in person before.  The first of these was in Ohio, where on May 26 I came across a musclewood tree (Carpinus caroliniana) with brown, crinkled blotch mines in the leaves, some of which started with a narrow linear portion.  After examining a few mines, I saw that some had a spherical bulge indicating where the larva had spun a cocoon.  Once I discovered this, I knew I had found the mines of some kind of weevil, as described on p. 356.

Larval mine of Orchestes mixtus (Curculionidae), a flea weevil, in a musclewood leaf. Also note the feeding holes made by adults.

I opened one of the mines up, and sure enough, I found the pale, twitching pupa of a weevil, recognizable by the long snout.

Exarate pupa of Orchestes mixtus, placed on its back so that the head, legs, and wings are visible.

I collected a few leaves in a vial, which I kept in a cooler until I got home.  On June 3 I looked in the vial and found three little adult weevils, which had emerged some time in the four days since I had last checked.  They were a type of flea weevil, so called because (like chrysomelid flea beetles, some of which also happen to be leafminers) they are small and jumpy.

An adult Orchestes mixtus. (2.5 mm)

Using Anderson (1989)* I was able to determine that the weevils were Orchestes mixtusO. pallicornis is essentially identical and would require dissection to distinguish in the absence of host plant information, but that species only feeds on trees in the rose family, whereas O. mixtus feeds on elms as well as various members of the birch family.  As of 1989, adults had been found on musclewood but no one had documented them emerging from mines in this host.

In the process of figuring out what species I had, I discovered an error in my book, which I suppose will only matter to those of you who care about Latin names and aren’t content to just call these things “flea weevils.”  The paragraph on flea weevils starts with “The sixteen species of flea weevils (Curculionidae: Orchestes) . . .”  In fact there are only six known Orchestes species in North America, one of which is introduced from Europe and was first documented in 2007.  The Latin name I should have used to encompass the flea weevils is the tribe Rhamphini, which also includes five Isochnus species and three Tachyerges species.  This adds up to fourteen, and I think the rest of the difference can be accounted for by species that turned out to be synonymous.  I think that my error came from having read that there were sixteen species of Rhynchaenus — the genus in which all North American flea weevils were once placed — and incorrectly assuming that all of them had been changed to Orchestes.  I also notice that Anderson doesn’t mention oak and maple as hosts of any flea weevils, so I suspect that my source for these associations was based on adults having been collected on oak and maple without any proof that these were actually host plants.  Ah well… I’ll try to get this straightened out in the second printing.

* Anderson, Robert S. 1989. Revision of the subfamily Rhynchaeninae in North America (Coleoptera: Curculionidae). Transactions of the American Entomological Society 115(3): 207-312.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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2 Responses to Leaf-mining Weevils

  1. Pingback: Leaf-rolling Weevils | BugTracks

  2. Pingback: A Stylish Little Wasp | BugTracks

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