As their common name suggests, adult eggplant tortoise beetles are shaped like tortoises. They are a yellowish green color, and their head and claws are hidden from above. The body is also flattened. The elytra, which cover the wings and are extended beyond the body, contain a series of punctures that stretch from the front to the back of the entire body.
Larvae are usually yellow-green in color and 5.5 mm when full grown.
The eggs of G. pallidula are oval shaped and a creamy to light brown color. They are usually 1.3 mm by 0.7 mm. A rectangular, brown, transparent membrane covers the egg. (Blatchely, 1926; Rolston, et al., 1965)
Gratiana pallidula is found wherever host plants of the genus Solanum grow. Solanum melongena, S. carolinese, S. xantii, and S. elaegnifolium are the main host plants. S. melongena is not found in the wild, but is instead grown in gardens. S. carolinese can live in a variety of habitats, including prairies, forest edges, roadsides, fields, and vacant lots. S. elaegnifolium is also a weed-like plant that lives in many habitats. It is found throughout most of the United States. S. xanti grows in the southwestern United States in chaparrals, woodlands and forests. (Blatchely, 1926; Imura, 2003; Olckers and Zimmermann, 1991; Rolston, et al., 1965)
Gratiana pallidula undergoes complete metamorphosis, and goes through egg, larva, pupa, and adult stages. First generation eggs are laid as early as May by adults that have emerged from hiding during the winter, while a second generation of eggs are laid in June or July. Larvae emerge after about a week or two. The larval stage of G. pallidula consists of five stages called instars. Larvae sometimes leave the host plant before pupating. Pupae form anywhere from a week to 3 weeks later, and attach to host plant leaves for 2 to 10 days. First generation adults usually emerge beginning in late June; second generation adults emerge in early August. From late August to early September they go into hibernation for the winter. One generation generally takes about 30 to 35 days to go from egg to adult. (Rolston, et al., 1965)
Little information is available on the mating systems of Gratiana pallidula.
Each year, G. pallidula has two generations that overlap, with one generation born in May-June, and the other generation born in August. Eggs are laid on the leaves of Horsenettle (Solanum). Usually eggs are laid singly, but are occasionally found in groups of 2. Additionally, G. pallidula is able to cross-breed with another species of tortoise beetle, G. lutescens, and produce offspring. (Olckers and Zimmermann, 1991; Rolston, et al., 1965)
Females provide nutrients in the eggs for the offspring to grow and develop. Otherwise, eggs are likely left on plants to hatch on their own, with no care from the parents. (Rolston, et al., 1965)
Gratiana pallidula is a herbivore that feeds on Solanum plants, particularly eggplant (S. melongena), common horsenettle (S. carolinese), gray horsenettle (S. xantii) and white horsenettle (S. elaegnifolium). Adults chew small, circular holes in leaves. During early larval instars, larvae feed on old leaves and green stems. The later instars feed on leaves and young growth. Before pupating, larvae live for 1 to 5 days without eating. Toward the end of summer, adults eat less. After emerging in the spring after hiding during the winter, adults eat more than normal. (Blatchely, 1926; Imura, 2003; Olckers and Zimmermann, 1991; Rolston, et al., 1965)
The stinkbug Stiretrus anchorago is a predator of G. pallidula larvae. Ants are also known to prey on larvae of the genus Gratiana, and are likely predators of G. pallidula as well. To defend against predators, the larvae of G. pallidula make shields on their backs out of feces. Instead of getting rid of their waste, it collects on a fork that sticks out from the end of their body. Larvae will also collect molted skin in their shields. Predators are more likely to stay away because of this fecal shield. (Eisner and Eisner, 2000; Rolston, et al., 1965; Scholtens, 2012)
Eggplant tortoise beetles feed on Solanum plants, particularly eggplant (S. melongena), common horsenettle (S. carolinese), gray horsenettle (S. xantii) and white horsenettle (S. elaegnifolium). G. pallidula are used as a host by parasitic wasps, Tetrastichus and Spilochalcis. Tetrastichus develops in the eggs G. pallidula and emerges 7 to 15 days later. S. sanguineiventris develops in the pupae of G. pallidula and emerges 12 to 18 days later. (Askew, 1971; Carasi and Teixeira, 2010; Olckers and Zimmermann, 1991; Rolston, et al., 1965)
Gratiana pallidula feeds on and infests Solanum plants, particularly eggplant (S. melongena), common horsenettle (S. carolinese), gray horsenettle (S. xantii) and white horsenettle (S. elaegnifolium). Both adults and larvae eat holes in the leaves of host plants, causing damage to the plant. For crops such as eggplant, which are eaten by G. pallidula, this can lead to economic loss on the damaged crops. (Carasi and Teixeira, 2010; Olckers and Zimmermann, 1991)
There are no known positive effects of G. pallidula on humans.
Gratiana pallidula is not an endangered species.
Jaclyn Tolchin (author), University of Michigan Biological Station, Angela Miner (editor), Animal Diversity Web Staff.
Askew, R. 1971. Parasitic insects. London, Great Britain: Heinemann Educational Books Ltd.
Blatchely, W. 1926. An illustrated descriptive catalogue of the Coleoptera or beetles known to occur in Indiana. Indianapolis, Indiana: WM. B. Burford, Contractor for State Publishing and Printing.
Eisner, T., M. Eisner. 2000. Defensive use of a fecal thatch by a beetle larva (Hemisphaerota cyanea). Proceedings of the National Academy of Sciences of the United States of America, 97/6: 2632-2636.
Fernandez, P., M. Hilker. 2007. Host plant location by Chrysomelidae. Basic and Applied Ecology, 8: 97-116.
Imura, O. 2003. Herbivorous arthropod community of an alien weed Solanum carolinense L. Applied Entomology and Zoology, 38: 293–300.
Olckers, T., H. Zimmermann. 1991. Biological control of silverleaf nightshade, Solanum elaeagnifolium, and bugweed, Solanum mauritianum, (Solanaceae) in South Africa. Agriculture, Ecosystems and Environment, 37: 137-155.
Scholtens, B. 2012. "Stiretrus anchorago" (On-line). Animal Diversity Web. Accessed July 31, 2012 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Stiretrus_anchorago.html.