Fecal shield

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Cassida viridis larva with fecal shield Cassida viridis Schildkafer (Chrysomelidae).P8193313 NEAT.jpg
Cassida viridis larva with fecal shield

The fecal shield is a structure formed by the larvae of many species of beetles in the leaf beetle family, Chrysomelidae. [1] It is composed of the frass of the insect and often its exuviae, or bits of shed exoskeleton. The beetle may carry the shield on its back or wield it upon its posterior end. The main function of the fecal shield is defense against predators. [2] Other terms for the fecal shield noted in the literature include "larval clothing", "kotanhang" ("fecal appendage"), "faecal mask", "faecal pad", and "exuvio-faecal annex". [3]

Contents

Ecology

Beetle larvae of the chrysomelid subfamilies Criocerinae and Galerucinae often wear their fecal shields in piles on their backs, regularly adding material as bits chip off. The shields of Cassidinae larvae are mobile. They are attached to the posterior end of the body and moved into position as needed, sometimes held in place above the larva like an umbrella. They may be raised and even swung to strike a predator. [4]

Cassida cf rubiginosa larva constructing the shield

When the shield is carried on the tip of the abdomen, it is secured to a double-lobed, spine-like process called the caudal furca, [5] which is also known as the "anal fork". [6] The larva constructs the shield by maneuvering its "muscular telescopic and highly protrusible anus", [7] or "anal turret", which is positioned dorsally, on the back. It excretes an amount of feces, sometimes with a droplet of gluey secretion, and places it on the caudal furca using its anal turret. In the species Hemisphaerota cyanea , the larva constructs a shield which may be more descriptively called a "fecal thatch", because it is woven from narrow, coiled strands of frass. The larva begins feeding immediately upon emergence from the egg and within minutes it produces its first fecal strand. Within twelve hours, its thatch-shield is full-sized. The larva diligently repairs the shield with replacement strands when it is broken. [8]

The fecal shield takes many forms across species. In some, it covers the entire body, while in others it is narrower. [8] In some, it is simply a "clump". [3] In consistency it may be hard or rather "pasty". [8] In some species of the subfamily Chrysomelinae, the female adult coats each of her eggs with feces, and when the larva emerges, it uses this ready-made fecal casing as the base of its shield, adding to it as it grows. These casings tend to be quite hard, and have been compared to adobe. [4] Most fecal shields are bound with exuviae, the "skins" shed from the insect when it molts. [3] Some shields, such as that of Cassida stigmatica , are entirely frass-free, made only of exuviae. [9]

Function

The fecal shield is not just a physical barrier, but also a chemical one. When a larva feeds on a plant, it ingests secondary metabolites in the plant tissues, such as alkaloids, saponins, and phytol derivatives, and these are present in its feces. These chemicals can be a potent defense against predatory insects. For example, the larva of the tortoise beetle Plagiometriona clavata obtains chemical compounds from its diet of bittersweet ( Solanum dulcamara ), excretes them, and incorporates them into its shield, where they repel the predatory ant Formica subsericea . [10]

The fecal shield is beneficial, but it is not without its cost to the insect. Though it is made of waste products, the larva must exert energy simply to transport its weight. [2] A fecal shield can weigh half as much as the larva itself. [11] This energy might otherwise go into development. [2] The shield is also a problem for the larva when it has the opposite effect: its chemistry attracts predators instead of repelling them. Experiments with several larvae of genus Cassida that feed on volatile-rich tansy show that their shields attract the predatory ant Myrmica rubra . [9]

Another possible function of the fecal shield may include protection of the larva from environmental conditions such as ultraviolet radiation, desiccation, wind, and rain. [2]

See also

Camptosomata

Other leaf beetle larvae build a case made of waste materials. Examples are: Exema and Neochlamisus .

Related Research Articles

Leaf beetle Family of beetles

The insects of the beetle family Chrysomelidae are commonly known as leaf beetles, and include over 37,000 species in more than 2,500 genera, making up one of the largest and most commonly encountered of all beetle families. Numerous subfamilies are recognized, but the precise taxonomy and systematics are likely to change with ongoing research.

Frass Waste from insects

Frass refers loosely to the more or less solid excreta of insects, and to certain other related matter.

<i>Neochlamisus</i> Genus of beetles

Leaf beetles of the genus Neochlamisus are sometimes known as the warty leaf beetles. They are members of the case-bearing leaf beetle group, the Camptosomata. Measuring 3–4 millimeters in length as adults, they are cryptic, superficially resembling caterpillar frass. Seventeen, sometimes 18 species are presently accepted in this genus, all of them occurring in North America.

Cassidinae Subfamily of beetles

The Cassidinae are a subfamily of the leaf beetles, or Chrysomelidae. The antennae arise close to each other and some members have the pronotal and elytral edges extended to the side and covering the legs so as to give them the common name of tortoise beetles. Some members, such as in the tribe Hispini, are notable for the spiny outgrowths to the pronotum and elytra.

<i>Charidotella sexpunctata</i> Species of beetle

Charidotella sexpunctata, the golden tortoise beetle, is a species of beetle in the leaf beetle family, Chrysomelidae. It is native to the Americas.

<i>Epargyreus clarus</i> Species of butterfly

Epargyreus clarus, the silver-spotted skipper, is a butterfly of the family Hesperiidae. It is claimed to be the most recognized skipper in North America. E. clarus occurs in fields, gardens, and at forest edges and ranges from southern Canada throughout most of the United States to northern Mexico, but is absent in the Great Basin and western Texas.

<i>Diamphidia</i> Genus of beetles

Diamphidia or Bushman arrow-poison beetle, is an African genus of flea beetles, in the family Chrysomelidae.

Thistle tortoise beetle Species of beetle

The thistle tortoise beetle is a species of leaf beetle, situated in the subfamily Cassidinae and the genus Cassida.

<i>Acromis spinifex</i> Species of beetle

Acromis spinifex is a species of tortoise beetle from South America. The males have enlarged elytra which are probably used in male–male combat, while females are among the few tortoise beetles to show maternal care of their offspring.

Insects have a wide variety of predators, including birds, reptiles, amphibians, mammals, carnivorous plants, and other arthropods. The great majority (80–99.99%) of individuals born do not survive to reproductive age, with perhaps 50% of this mortality rate attributed to predation. In order to deal with this ongoing escapist battle, insects have evolved a wide range of defense mechanisms. The only restraint on these adaptations is that their cost, in terms of time and energy, does not exceed the benefit that they provide to the organism. The further that a feature tips the balance towards beneficial, the more likely that selection will act upon the trait, passing it down to further generations. The opposite also holds true; defenses that are too costly will have a little chance of being passed down. Examples of defenses that have withstood the test of time include hiding, escape by flight or running, and firmly holding ground to fight as well as producing chemicals and social structures that help prevent predation.

<i>Phratora vitellinae</i> Species of beetle

Phratora vitellinae, the brassy leaf beetle, formerly Phyllodecta vitellinae, is a beetle of the family Chrysomelidae found in Europe and Asia. It feeds on Populus and Salix species. The evolution of its host plant preferences and the mechanism by which it uses host plant chemicals to make a larval defensive secretion have been the subject of intense study by research groups in Europe and the Nordic countries.

<i>Deloyala guttata</i> Species of beetle

Deloyala guttata, the mottled tortoise beetle, is a species of tortoise beetle in the family Chrysomelidae. It is found in the Caribbean, Central America, North America, and South America.

<i>Chelymorpha cassidea</i> Species of beetle

Chelymorpha cassidea, known generally as the Argus tortoise beetle or milkweed tortoise beetle, is a species of leaf beetle in the family Chrysomelidae. It is found in the Caribbean and North America.

<i>Hemisphaerota cyanea</i> Species of beetle

Hemisphaerota cyanea, known generally as palmetto tortoise beetle, is a species of leaf beetle in the family Chrysomelidae. Other names include the Florida tortoise beetle and iridescent blue chrysomelid beetle. It is native to the southeastern United States, from North Carolina, south to Florida, and west to Mississippi. It is introduced to southern Texas.

<i>Hemisphaerota</i> Genus of beetles

Hemisphaerota is a genus in the subfamily Cassidinae in the family Chrysomelidae. There are about 10 described species in Hemisphaerota.

Hemisphaerotini Tribe of beetles

Hemisphaerotini is a Neotropical tribe of tortoise beetles and hispines in the family Chrysomelidae. There are at least 2 genera and more than 40 described species in Hemisphaerotini.

<i>Eurypepla calochroma</i> Species of beetle

Eurypepla calochroma, commonly known as the Geiger tortoise beetle, is a species of tortoise beetle. It is found in Florida, Central America and the Caribbean. This specific beetle only feeds on the Geiger tree throughout all of its life stages.

<i>Epistictina reicheana</i> Species of beetle

Epistictina reicheana, is a species of leaf beetle found in India, Nepal, Sri Lanka and Tasmania.

Laccoptera (Laccopteroidea) quatuordecimnotata, is a species of leaf beetle native to India, and Sri Lanka.

Silana farinosa, commonly known as curry-leaf tortoise beetle, is a species of leaf beetle native to Indo-China, India, Sri Lanka, Thailand and introduced to Peninsular Malaysia.

References

  1. ↑ Nogueira-de-Sá, F. and J. R. Trigo. (2002). Do fecal shields provide physical protection to larvae of the tortoise beetles Plagiometriona flavescens and Stolas chalybea against natural enemies? Entomologia Experimentalis et Applicata 104(1) 203-06.
  2. 1 2 3 4 Bacher, S. and S. Luder. (2005). Picky predators and the function of the faecal shield of a cassidine larva. Functional Ecology 19(2) 263–72.
  3. 1 2 3 Gómez, N. E., et al. (1999). Chemical defense in larval tortoise beetles: essential oil composition of fecal shields of Eurypedus nigrosignata and foliage of its host plant, Cordia curassavica. Journal of Chemical Ecology 25(5) 1007-27.
  4. 1 2 Chaboo, C. Defensive behaviors in leaf beetles: from the unusual to the weird. Archived 2013-12-07 at the Wayback Machine Pp. 59-69. In: Vivanco, J. and T. Weir (Eds.) Chemical Biology of the Tropics. Springer Verlag, Berlin. 2011.
  5. ↑ Gomes, P. A., et al. (2012). Biology of Omaspides pallidipennis Boheman, 1854 (Coleoptera: Chrysomelidae: Cassidinae). Psyche: A Journal of Entomology 2012 290102.
  6. ↑ Capinera, J. Golden Tortoise Beetle. Entomology and Nematology. University of Florida IFAS. 1997, revised 2012.
  7. ↑ Keefover-Ring, K. (2013). Making scents of defense: do fecal shields and herbivore-caused volatiles match host plant chemical profiles? [ permanent dead link ]Chemoecology 23(1) 1-11.
  8. 1 2 3 Eisner, T. and M. Eisner. (2000). Defensive use of a fecal thatch by a beetle larva (Hemisphaerota cyanea). Proceedings of the National Academy of Sciences 97(6) 2632-36.
  9. 1 2 Müller, C. and M. Hilker. (1999). Unexpected reactions of a generalist predator towards defensive devices of cassidine larvae (Coleoptera, Chrysomelidae). Oecologia 118(2) 166-72.
  10. ↑ Vencl, F. V., et al. (1999). Shield defense of a larval tortoise beetle. Journal of Chemical Ecology 25(3) 549-66.
  11. ↑ Mitton, J. Tortoise beetles and fecal shields. Colorado Arts and Sciences Magazine. College of Arts and Sciences. University of Colorado, Boulder. 2010.
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