geometrid moths

Twig tethered to a twig

/ Ted C. MacRae / 1 Comment
Geometrid larva (subfamily Ennominae?) | Plymouth, North Carolina

Geometrid larva (subfamily Ennominae?) | Plymouth, North Carolina

In September I visited soybean field trials across the southeastern U.S. It’s a trip I’ve done every year for the past I don’t know how many years and one that I enjoy immensely due to the opportunities it gives me to see the country, kick the dirt with academic cooperators, sample the local cuisine… and photograph insects. New for me this year was the Carolinas, and in a soybean field in Plymouth, North Carolina I encountered this geometrid larva on the stub of a soybean leaf petiole. Geometrid larvae are known variously as inchworms, cankerworms, spanworms, measuring worms, loopers, etc., depending on the species. Most of the common names refer to the same thing that the family name does—the larval method of locomotion whereby the caterpillar—possessing legs only at the two extremes of its body—”inches” its way along as if measuring the ground it walks on (Geometridae is derived from the Latin geometra, or “earth-measurer”). The resemblance of the larvae of many species to dead twig stumps is nothing short of remarkable, and had it not been for the contrasting coloration I may never have noticed the larva in the first place. I also did not notice until looking at it through the macro lens of my camera the tether attached by the larva to the tip of the twig—invisible to the naked eye but providing energy-saving stabilization for the larva to hold its cryptic position.

I’ve not encountered a geometrid larva in soybeans before, and my impression has been that they are largely deciduous tree feeders (perhaps due to the periodic occurrence in my area of outbreak species such as fall cankerworm). In trying to determine the species, I found no geometrids covered in the Higley & Boethel (1994) handbook on U.S. pests, and when I consulted the Turnipseed & Kogan (1976) and Kogan (1987) global reviews of soybean pests I found reference only to a few minor pests in India and southeast Asia. Hmm, time for BugGuide. Of course, lepidopteran larvae are not nearly as well represented as the adults, but it seemed most similar to species of the subfamily Ennominae, so I turned to Google and searched on “Ennominae soybean.” This turned up Passoa (1983), who reported larvae of Anacamptodes herse as pests of soybean in Honduras (and mentioned references to several other geometrid species associated with soybean in Brazil). Back to BugGuide, where I found the genus Anacamptodes listed as a synonym of Iridopsis, but the species I. herse was not among the list of species represented in the guide. Checking the link provided at the site to a revision of the genus by Rindge (1966) revealed that I. herse is strictly a Central American species. Perhaps another, North American species of the genus also favors soybean, which led me to Wagner (2005) who mentions soybean as a favored food plant for I. humilis. However, the contrasting purple-brown/yellow-green coloration and relatively thickened body of that species are quite unlike this individual. I don’t have Wagner’s book (only his smaller one on caterpillars of eastern forests—no match in there, either), so it may be that my only remaining option is to post the photo at BugGuide and hope that David Wagner encounters it (actually I should get David’s book anyway)¹.

¹ Update 10/5/13 11:30 am CDT—or hope that Brigette Zacharczenko runs into the post via Facebook and offers to pass it along to Dave during their lab meeting on Monday.

REFERENCES:

Higley, L. G. & D. J. Boethel [eds.]. 1994. Handbook of Soybean Insect Pests. The Entomological Society of America, Lanham, Maryland, 136 pp. [sample pages].

Kogan, M. 1987. Ecology and management of soybean arthropods. Annual Review of Entomology 32:507–538 [pdf].

Passoa, S. 1983. Immature stages of Anacamptodes herse (Schaus) (Geometridae) on soybean in Honduras. Journal of The Lepidopterists’ Society 37(3):217–223 [pdf].

Rindge, F. H. 1966. A revision of the moth genus Anacamptodes (Lepidoptera, Geometridae) (1966). Bulletin of the America Museum of Natural History 132(3):174–244 [pdf].

Turnipseed, S. G. & M. Kogan. 1976. Soybean entomology. Annual Review of Entomology 21:247–282 [pdf].

Wagner, D. L. 2005. Caterpillars of Eastern North America: A Guide to Identification and Natural History . Princeton University Press, Princeton, New Jersey, 496 pp. [Google eBook].

Copyright © Ted C. MacRae 2013

Monday Moth: White-tipped Black Moth

/ Ted C. MacRae / 24 Comments
Melanchroia_chephise_IMG_1241_1200x800_enh

Photo details: Canon 100mm macro lens on Canon 50D (manual mode), ISO-100, 1/250 sec, f/22, MT-24EX flash w/ Sto-Fen diffusers.

When is a ctenuchid moth not a ctenuchid moth?  When it’s a White-tipped Black Moth (Melanchroia chephise) in the family Geometridae!

I may be a beetle guy, but I also consider myself a competent general entomologist.  What is a competent general entomologist?  Someone who can identify any insect to order at first glance and a majority of them to family – regardless of one’s own taxa of expertise.  Thus, when I encountered this mating pair of moths on the outside wall of my sister-in-law’s condominium in Seminole, Florida, I “recognized” them as something in what I learned as the family Ctenuchidae (later subsumed within the Arctiidae, first as a subfamily and now as several disparate tribes).  They had all the hallmarks of ctenuchids—black and red coloration, narrowish wings with light colored patches, and about the size of the wasps that they presumably mimic.  Upon my return to St. Louis, I sat down to identify the moths—confident that their distinctive appearance would lead to the quick ID that never materialized after scanning through all of the ctenuchine pages at BugGuide.  Frustrated, I resorted to posting the photo on the site’s ID Request, never questioning my ctenuchine placement.  Precisely 4 minutes later, the moths were identified by John Maxwell as Melanchroia chephise and moved to their proper place—among the 50 other adult photographs of this species that can be found on the site!  I might as well have failed to identify a monarch butterfly!

Melanchroia chephise is apparently common in the American tropics, reaching its northern distributional limit along the coastal plains of Florida and Texas but straying further north in certain years.  Larvae feed on several plants in the family Euphorbiaceae, primarily Breynia and Phyllanthus species.  The adult coloration strikes me as obviously aposematic (warning coloration), but I could find no specific references to this.  However, considering that euphorbiaceous plants are famous for their diverse arsenal of latex and irritant toxins (e.g., diterpene esters, alkaloids, glycosides, ricin-type protein toxins, etc.), it seems reasonable to presume that Melanchroia larvae have evolved mechanisms for sequestering one or more of these compounds.  NABA South Texas states that adults of this species are probably mimics of the Red-bordered Pixie (Melanis pixe), an aposematic metalmark butterfly also of Neotropical distribution that reaches south Texas (but not Florida).  Personally, I don’t really see the resemblance (but then, nor am I an avian predator).  I suppose it’s possible that a species such as this can employ different defense strategies in different parts of its range, relying on Batesian mimicry in areas where suitable models occur and aposematism in areas where they don’t, but I have to admit that I’m now straying well outside the coleopteran-centric bounds of my expertise.

Copyright © Ted C. MacRae 2009

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