Fascinating Insect with a William M. Ciesla I n 1997, I was working in Port of Spain, on the Caribbean Island of Trinidad. As I walked past the Botanical Gardens opposite Queen s Park Savannah, I couldn t help but notice large numbers of caterpillars feeding on the foliage of several frangipani trees, Plumeria spp., in the garden. It had been a long day and I had a report to finish that evening, so they only received a cursory examination and were soon forgotten. In 2004, on a more leisurely visit to the neighboring island of Tobago, I saw them again. This time, they appeared on the foliage of giant milkweed, Calotropis procera, 76 a plant on which I would have expected to see larvae of the monarch butterfly, Danaus plexippus. During a stop at an Internet café, I Googled frangipani and sphinx moth and quickly identified the larvae as Pseudosphinx tetrio (L.) (Lepidoptera: Sphingidae). I found that it was a relatively well known species with several common names, including tetrio sphinx, giant gray sphinx, and frangipani hornworm (Dunford and Barbara 2005). In 2012, while visiting the British and U.S. Virgin Islands, my wife, Pat, and I encountered outbreak populations of P. tetrio in several locations, American Entomologist Summer 2013 A Close Encounter
which provided an opportunity to learn more about this fascinating and colorful insect (Fig. 1). Fig. 1. Mature larva of Pseudosphinx tetrio; Norman Island, British Virgin Islands. Distribution and Hosts Santiago-Blay 1985). In addition to Trinidad and Tobago, the author has seen life stages on Norman Island, British Virgin Islands and on St. John, U.S. Virgin Islands. The primary host plants are species of frangipani, Plumeria spp., including P. alba, P. rubra, and P. obtusa (Family Apocynaceae) (Fig. 2). Frangipani is a popular ornamental tree and helps create a tropical appearance in urban areas. Its waxy flowers emit a lemon or P. tetrio is widely distributed in the tropical and subtropical regions of the Americas, from southern Brazil and Paraguay north through Central America, Mexico, the Caribbean Basin, and the southern United States. Moths have been collected as far north as Connecticut, Nebraska, and Pennsylvania, but there are no suitable host plants for the larvae in these locations (Dunford and Barbara 2005, American Entomologist Volume 59, Number 2 77
Rico. He also reports that larvae fed reluctantly on A. cathartica in the laboratory and rejected foliage of Pterocarpus indicus, Carica papaya, Bambusa vulgaris, Lagerstroemia speciosa, Calotropis procera, and Wedelia trilobata. This author s observation of larvae feeding on C. procera on Tobago may be an anomaly (Fig. 3). Mature or nearly mature larvae were found feeding on a single plant near the community of Plymouth, on the northwest shore of the island of Tobago in February 2004. Neighboring C. procera plants were free of P. tetrio larvae, although (as expected) they did contain small numbers of larvae of Danaus plexippus. Fig. 2. Species of frangipani, Plumeria spp., are the primary host plants for larvae of Pseudosphinx tetrio. gardenia-like fragrance and are used for making traditional leis in Hawaii. Like other plants of the family Apocynaceae, frangipanis produce a toxic milky sap that contains alkaloids. Other reported host plants of P. tetrio include Allamanda cathartica (golden trumpet), Himatanthus sucuuba (bellaco-caspi), Rhabdadenia biflora (Florida rubbervine), and Echites umbellata (devil s potato) (Dunford and Barbara 2005). Santiago-Blay (1985) reports a single occurrence of larvae feeding on Allamanda cathartica in Puerto 78 P. tetrio has multiple generations and life stages can be found throughout the year, except in locations where there are prolonged dry seasons and frangipani, its principal host, drops its leaves and becomes dormant. Female adults deposit eggs in masses of 50 to 100, usually on the undersides of leaves of host plants. Eggs are pale green and ellipsoidal when deposited. They hatch within about three days, and all the eggs hatch at about the same time (Santiago-Blay 1985). After eclosion, eggs are milky white (Fig. 4). Larvae are gregarious and live in colonies for at least the first three instars. Initial feeding is on the upper surface of the leaf (Fig. 5). Later instars consume all of the leaf tissue except veins and midribs, and mature larvae consume entire leaves. As leaves are consumed, the larval colony moves in unison to a new feeding site (Fig. 6). According to Santiago-Blay (1985), most larvae have five instars, although a few individuals undergo Fig. 3. Larva of Pseudosphinx tetrio on giant milkweed, Calotropis procera; Plymouth, Tobago. American Entomologist Summer 2013 Life History and Habits
Fig. 4. Recently hatched egg mass of Pseudosphinx tetrio; St. John, U.S. Virgin Islands. a sixth instar. Mature larvae are either solitary feeders or feed in small groups. The coloration of the larvae is quite striking. Their bodies are velvety black with yellow rings on each thoracic and abdominal segment, the head is dark red-orange, and the prothoracic shield, legs, prolegs, and anal segment are red-orange with dark brown mottling. The spine on the eighth abdominal segment is black and emerges from an elevated, orange, button-like structure. Newly molted larvae are lighter in color. Mature larvae range in length from 63-69 mm (Houge 1993, Santiago-Blay 1985, Fig. 1). The characteristic larval coloring is an example of aposematism and serves as a warning to would-be predators that the larvae are (at best) bad-tasting and (at worst) toxic. One author has suggested that the larval coloration resembles that of the poisonous Central American coral snake, Micrurus nigrocinctus, and its Spanish common name is oruga falso-coral (Janzen 1980, 1983). When feeding is complete, larvae drop to the soil or leaf litter, spin loose cocoons of silk and leaf litter, and pupate. The elongated pupae are yellow at first and turn dark brown within a few days (Santiago-Blay 1985). In Florida, several adult flights occur between March and September (Dunford and Barbara 2005). A single adult was collected on St. John, USVI, 23 December 2012. The adults have a wingspan of 12.7 14.0 cm, and females are slightly larger than males. The body is light brown and the forewings have a faint mottled pattern, American Entomologist Volume 59, Number 2 Fig. 5. Colony of first instar larvae of Pseudosphinx tetrio. Note feeding damage on upper surface of frangipani leaf; St. John, U.S. Virgin Islands. while the hind wings are medium brown with white along the inner margin (Fig. 7). Male moths are somewhat darker than females. Both sexes are strong fliers. Generally nocturnal, they are attracted to several species of flowering plants from which they gather nectar and serve as pollinators (Dunford and Barbara 2005). A laboratory study indicates that total life span from egg to adult is about 53 days, with approximately three days as eggs, 24 days as larvae, 4 days as prepupae, and 22 days as pupae (Santiago-Blay 1985). 79
Santiago-Blay (1985) reports the presence of tiny holes in two eggs that failed to hatch during a laboratory study, suggesting the activity of an egg parasite. On Tobago, approximately 50% of the late-instar larvae feeding on Calotropis procera exhibited flaccid bodies and were hanging from branches and leaf petioles, symptoms suggestive of infection by a virus (Fig. 8). As would be expected of aposematic larvae, there are few reports of larval predation. However, in Belize, the squirrel cuckoo, Piaya cayana, has been observed taking P. tetrio larvae, beating them against a branch until the gut content is gone, and swallowing the remains (Meerman 2009). Fig. 7. Pseudosphinx tetrio adult; Cruz Bay, St. John, U.S. Virgin Islands. 80 Fig. 6. After devouring all of the foliage on a branch, a colony of Pseudosphinx tetrio larvae move in unison to a new feeding site; Norman Island, British Virgin Islands. Socio-Economic Impacts Mature larvae are capable of consuming three leaves per day, and large numbers of larvae can cause moderate to heavy defoliation of host plants (Fig. 9). However, reports of permanent injury to host plants (such as growth loss, dieback, or mortality, often associated with insect defoliation) are lacking. A few detrimental effects on humans associated with the larvae of P. tetrio are reported. In one instance, an individual who was clearing vegetation from his garden Fig. 8. Mature larva of Pseudosphinx tetrio with symptoms suggestive of virus infection; Plymouth, Tobago. American Entomologist Summer 2013 Natural Enemies
Save Money, Save Time. Get Results! With our high quality Lepidoptera Eggs and Larvae Beet Army Worm Cabbage Looper Corn Earworm Diamondback Moth Fall Armyworm Tobacco Budworm Fig. 9. Defoliation of frangipani by Pseudosphinx tetrio; Cruz Bay, St. John, U.S. Virgin Islands. developed keratitis (inflammation of the cornea of the eye), which was attributed to the fine hairs of P. tetrio larvae (Merle et al. 2001). Larvae reportedly wave their anterior back and forth when disturbed and will bite when handled (Houge 1993, Janzen 1980). Having been bitten by a mature larva of the tobacco hornworm, Manduca sexta (L.), many years ago, this author can confirm that larvae the size of a mature P. tetrio could deliver a nasty bite. On Tobago, local folklore suggests that exposure to larvae of both P. tetrio and D. plexippus causes fever. Presence of large numbers of larvae in urban areas is a potential nuisance, yet people on the U.S. Virgin Island of St. John seem to regard them as objects of curiosity and fascination. References Cited Dunford, J.C., and K.A. Barbara. 2005. Tetrio sphinx, giant gray sphinx, frangipani hornworm, Pseudosphinx tetrio (Linnaeus) (Insecta: Lepidoptera: Sphingidae). University of Florida, Institute of Food and Agricultural Sciences Extension, EENY344. Houge, C.L. 1993. Latin American Insects and Entomology. University of California Press, Berkeley, CA. Janzen DH. 1980. Two potential coral snake mimics in a tropical deciduous forest. Biotropica 12: 77-78. Janzen, D.H. 1983. Pseudosphinx tetrio (oruga falso-coral, frangipani sphinx), pp. 764-765. In Janzen, D.H. (ed.), Costa Rican Natural History. University of Chicago Press, Chicago, IL. Meerman J.C. 2009. The annual outbreak of colorful caterpillars of the frangipani hawkmoth (Pseudosphinx tetrio). Biological Diversity in Belize, Biological-Diversity. info., http://biological-diversity.info/pseudosphinx.htm (site visited 17 January 2012). Merle, H., D. Suchocki, M. Gérard, and A. Donnio. 2001. Keratitis due to caterpillar of Pseudosphinx tetrio hairs. Journal Français d Ophtalmologie 24: 635-638 (In French). Santiago-Blay, J.A. 1985. Notes on Pseudosphinx tetrio (L.) (Sphingidae) in Puerto Rico. Journal of the Lepidopterists Society 39: 208-214. William M. Ciesla is the owner of Forest Health Management International, an international consulting service based in Fort Collins, Colorado. American Entomologist Volume 59, Number 2 Entomology Division Lepidoptera Eggs and Larvae Insect Diets and Ingredients Rearing Supplies and Equipment 800-996-9908 U.S and Canada 908-996-2155 International sales@insectrearing.com www.insectrearing.com 81