Gratiana pallidula

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Geographic Range

Gratiana pallidula, also known as the eggplant tortoise beetle, is found in the Nearctic Region throughout the southern United States. (Olckers and Zimmermann, 1991)

Habitat

Gratiana pallidula is found where host plants are found. Solanum plants, such as S. melongena, S. carolinese, S. xantii, and S. elaegnifolium are the main host plants. S. melongena is not found in the wild, but is instead maintained in cultivated gardens. S. carolinese often takes advantages of disturbed areas and can thrive 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)

Physical Description

As their common name may suggest, adult eggplant tortoise beetles are shaped like tortoises. They are a yellowish green color with a concealed head and claws, which differentiates G. pallidula from other North American species of tortoise beetles. The body is also flattened, with a broad, expanded pronotum and elytral margins. The elytra contain a series of coarse punctures that stretch from the front to the back of the entire body.

Larvae are recognized by 16 pairs of subspiracular scoli, an anal fork, and retracted head. They are usually yellow-green in color and 5.5 mm when full grown.

The eggs of G. pallidula are capsular, oblong, 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)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    5 to 5.5 mm
    0.20 to 0.22 in

Development

Gratiana pallidula is holometabolous and goes through egg, larva, pupa, and adult stages. First generation eggs are laid as early as May by adults that have overwintered, 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 instars. Larvae sometimes leave the host plant before pupating. Pupae form anywhere from a week to 3 weeks later, and attach to the upper surface of 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)

Reproduction

Little information is available on the mating systems of Gratiana pallidula.

Each year, G. pallidula has two full generations that overlap. Eggs are laid on Horsenettle (Solanum) foliage, usually on the upper surface of a leaf or near the leaf terminals. Usually eggs are laid singly, but are occasionally found in groups, rarely containing more than two eggs. Additionally, G. pallidula is able to cross-breed with G. lutescens and produce fertile offspring. (Olckers and Zimmermann, 1991; Rolston, et al., 1965)

  • Breeding interval
    Two generations are born during the summer.
  • Breeding season
    The two main breeding times are May-June and August.

Females provide eggs with nutrients, but otherwise it is likely that eggs are left on plants to mature on their own. (Rolston, et al., 1965)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

Little information on lifespan is available, but it takes about 30 to 35 days for G. pallidula to go from egg to adult. Adults then likely live several weeks in the summer. (Rolston, et al., 1965)

Behavior

G. pallidula is diurnal. They remain on their host plants during the night. Daytime clouds and low temperatures reduce their activity. (Rolston, et al., 1965)

Communication and Perception

In general, leaf beetles in the Chrysomelidae family use visual, olfactory and chemical cues when colonizing a host plant. (Fernandez and Hilker, 2007)

Food Habits

Gratiana pallidula is a herbivorous oligophage 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 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 feeding. Toward the end of summer, adult feeding rates decrease, and then increase in early spring after diapause. (Blatchely, 1926; Imura, 2003; Olckers and Zimmermann, 1991; Rolston, et al., 1965)

  • Plant Foods
  • leaves

Predation

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. In defense, like all larvae of tortoise beetles in the family Cassinidae, the larvae of G. pallidula build fecal shields on their backs. Instead of getting rid of their waste, it accumulates on a fork that projects from the tip of the abdomen, forming a shield that effectively deters enemies. In addition to feces, larvae of G. pallidula will also accumulate molted larval skin in their shields. (Eisner and Eisner, 2000; Rolston, et al., 1965; Scholtens, 2012)

Ecosystem Roles

Eggplant tortoise beetles feed on and infest Solanum plants, particularly eggplant (S. melongena), common horsenettle (S. carolinese), gray horsenettle (S. xantii) and white horsenettle (S. elaegnifolium). G. pallidula serves as a host to parasitic wasps, Tetrastichus and Spilochalcis. Tetrastichus parasitize eggs and emerge 7 to 15 days later. S. sanguineiventris parasitize pupae and emerge 12 to 18 days later. (Askew, 1971; Carasi and Teixeira, 2010; Olckers and Zimmermann, 1991; Rolston, et al., 1965)

Species Used as Host
  • Solanum melongena
  • Solanum carolinese
  • Solanum xantii
  • Solanum elaegnifolium
Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of G. pallidula on humans.

Economic Importance for Humans: Negative

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, but larvae cause the most damage. (Carasi and Teixeira, 2010; Olckers and Zimmermann, 1991)

  • Negative Impacts
  • crop pest

Conservation Status

The IUCN Red List, CITES appendicies, the US Federal list or the State of Michigan list have no special status on G. pallidula.

Contributors

Jaclyn Tolchin (author), University of Michigan Biological Station, Angela Miner (editor), Animal Diversity Web Staff, Brian Scholtens (editor), University of Michigan Biological Station.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

diapause

a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

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.

Carasi, S., E. Teixeira. 2010. Immatures of Gratiana conformis (Bohemian) (Coleoptera, Chrysomelidae, Cassidinae). Revista Brasileira de Entomologia, 54: 235-242.

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.

Rolston, L., R. Mayers, P. Edwards, M. Windfield. 1965. Biology of the eggplant tortoise beetle (Coleoptera: Chrysomelidae). Journal of the Kansas Entomological Society, 38: 362-366.

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.