Sphinx Moths - October 18, 2006
Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Most gardeners have encountered a sphinx moth at one time or another. The tomato hornworm is a sphinx moth larvae and any vigilant tomato grower has plucked a few of these giants from their tomato plants. Others may have observed adult sphinx moths feeding on sacred datura, petunias, thistles, evening primroses, honeysuckle, verbena, salvia, Nicotiana, four-o-clocks, and other nectar producing flowers. Sphinx moths are also known as hawk moths and hummingbird moths. In southeastern Arizona, 45 species of sphinx moths have been collected. While I am not aware of any scientific data for our area, but I would guess we have at least 10 species.
In general, the life cycle of sphinx moths is similar for most species. The pupae overwinter in the soil in a 1 ½ to 2 inch long brownish case. When handled under warm conditions, a pupa will often begin to move. These pupae are often brought to our Cooperative Extension offices for identification. Adults emerge in spring or early summer then mate and lay eggs on suitable host plants for their species. Upon hatching, larvae often initially feed in groups then become solitary as they mature. After feeding for 6-8 weeks, the larvae burrow into the soil to pupate. Some species of sphinx moths are known to have up to four generations per year. The number of generations varies by species and location.
The tomato hornworm (Manduca quinquemaculata) and the tobacco hornworm (Manduca sexta) are both sphinx moths. The word “hornworm” describes the distinctive pointed structure on its tail. The tomato hornworm larva is green with diagonal white lines on the side of each segment that form L-shapes. The adults are large gray moths with a wingspan of five inches. They have four yellow-orange patches on each side of their abdomen. The tobacco hornworm is also found on tomatoes, but has a red "horn" and straight diagonal stripes. The adult looks similar to the tomato hornworm. Both feed on tomatoes and peppers and may even be present on the same plant. The larvae of each species can reach four inches in length. Experienced tomato growers monitor for damage and frass (droppings). The larvae are usually in the interior of the plant during daylight hours. Hand picking the larvae is the best control option for protection of home gardens.
Another common species in our area is the white-lined sphinx moth (Hiles lineata). The larvae of this species feed on a wide variety of host plants. The adult has distinctive pink patches on its underwings and is a very common visitor to flower gardens. During years when sphinx moth larvae are abundant and large migrations have occurred in the desert, there have reports of dangerous road conditions for vehicles due to an “oil slick effect”. This could be an urban legend, but it sounds feasible and sensational enough to make news.
This summer, Bob Celaya (Office of the State Forester) and I were in the field and he found a Great Ash Sphinx Moth (Sphinx chersis) larva on an ash tree. It is very similar in appearance to the tobacco hornworm, but does not have a red “horn”. In researching this column, I learned about sphinx moths that are known to feed on catalpa, poplar, cottonwood, incense cedar, juniper, mints, desert willow, and many other species that grow in our area. I imagine that if we went out and looked for various species, we may find as many as those documented in southeastern Arizona. The interesting thing about that is, since they do not form a web or cause noticeable damage outside of vegetable gardens, sphinx moth “damage” goes largely unnoticed.
There are many great web sites devoted to sphinx moths. If you are interested, visit the Moths of Southeastern Arizona web site at nitro.biosci.arizona.edu/zeeb/butterflies/mothlist.html. It has excellent pictures of the moths, larvae, and pupa of species discussed above and good scientific information.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: October 12, 2006
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