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The tortoise beetles and relatives constitute the leaf beetle subfamily Cassidinae. As of 2007, they contain about 6,000 species in roughly 2,000 genera, with new ones continuing to be described at a steady pace; consequently, they are the second-largest leaf beetle subfamily (after the Galerucinae). They are found almost worldwide, being absent only from New Zealand and the polar regions. But the subfamily is especially diverse in the Neotropics.

Taxonomy
The validity, rank and circumscription of this group has been very much disputed ever since the taxon's erection in 1813. Initially, they were treated at equal rank but distinct from the presumed lineage named Hispinae. This taxon, like the Cassidinae, was first proposed by Leonard Gyllenhaal (or "Gyllenhal" as he was then transliterated), an ancestor of modern actors Jake and Maggie Gyllenhaal. S. Chen, when revising the group in 1940, decided that should they form a single (monophyletic, in today's terminology) group of relatives the name Cassidinae should be the senior synonym.

The Cassidinae and "Hispinae" were lumped and split again by various authors times and again; Chen himself changed his opinion on this matter. This was largely a result of different analysis techniques, with the phenetic studies favored in the mid-late 20th century seemingly suggesting that the basal "Hispinae" formed a clade of their own. With the improved cladistic studies available at the end of the last century, it became clear that the "Hispinae" were actually a paraphyletic assemblage of plesiomorphic tortoise beetles, while the "true" tortoise beetles in the traditional sense and some very close relatives do indeed seem to form a clade within these. Consequently, the "Hispinae" are here merged in the Cassidinae, while the Cassidinae sensu stricto become the tribe Cassidini.

Description
The Cassidinae are fairly small beetles, though by leaf beetle standards they are of average size. They range from a few millimeters (e.g. the tiny Oxylepus) to several centimeters (e.g. Alurnus, which are among the largest leaf-eating insects). Very plesiomorphic lineages look much like robust, large Galerucinae. Their exoskeleton is tough, providing some protection from predators. But many lineages have evolved even better means to stay alive. Some of the more basal groups, such as certain Hispini, are covered in spines. While these do not deter a predator outright, they will make eating the beetle an unpleasant experience, and most predators will soon learn to prefer easier prey. Others, as well as many Cassidinae larvae, camouflage themselves with debris, even their own feces, which is held in place above their bodes with bristles.

Yet others – the tortoise beetles proper of tribes Cassidini, Dorynotini, Eugenysini, Hemisphaerotini and the doubtfully valid Ischyrosonychini – are shaped like a lentil or the carapace of a tortoise (hence their common name). Their thorax' tergites and the elytrae forming a homogenous surface that expands laterally and covers the entire beetle save the antennae. In combination with a smooth cuticula, this makes it very hard for any predator to pick up the beetle from the substrate. The tarsus of many Cassidinae is covered with bifid setae on the underside similarly to a gecko's toes, and between the setae an oily liquid with strong adhesive power was shown to be secreted in Hemisphaerota cyanea (the only species studied in such detail to date). This allows the beetle to achieve an extremely strong hold on surfaces – presumably due to the combination of the liquid's surface tension and the Van der Waals forces between setae and surface – which makes it even harder for a predator to dislodge the insect. It is not known, however, whether this type of adhesive apparatus is widely found among the Cassidinae, or whether other approaches or variants exist.

Many Cassidinae are brightly colored and/or metallic. Some are very cryptic regardless, with golden-green hues or transparent elytrae which afford good protection amongst foliage. Others are contrasting, even conspicuous in their environment; it may be that these are poisonous and warn off potential predators with aposematic coloration.

Life-history data is known for less than 10% of the described species.

The larvae of Cassidinae typically seem go through 3 or 4 instars, but it is suspected that this is actually biased due to a lack of knowledge. Promecotheca cumingi develops with only two instars, while at least some Cryptonychini have 6. Among Alurnini, Arescini and Cephaloleiini species with 8 instars to pupation have been recorded.

Ecology
Though generally found in habitat with a significant amount of woody plant growth, Cassidinae – at least the non-mining species – are rare by comparison to other leaf beetles in the forest canopy. Rather, they prefer more open habitat, such as roadsides, cuts, treefalls or patches of shrubland. In general, they live on their host plants, where the adults feed openly on the leaves. However, the adults of two Imatidium species apparently produce themselves shelters out of leaves, from which they then feed at leisure, as do larvae of the unrelated Leptispini. Almost 40% of the described Cassidinae are leaf miners as larvae, and a few Anisoderini and Cryptonychini are stem- or stalk miners. The larvae of some non-mining species in the Arescini and Cephaloleiini eat from young leaves that have not unrolled, and likewise utilize shelter when feeding. Some Cassindinae – namey the tortoise beetles – are free-roaming feeders even as larvae, however. A sixth feeding guild found among the larvae of this subfamily are those that inhabit the water-filled bracts of Heliconia and feed on flower parts; this behaviour probably evolved from rolled-leaf feeding.

The life cycle of Cassidinae takes usually a few weeks in tropical, a few months in temperate regions. There are some – in particular rolled-leaf feeders – which take much langer to develop. The record development times are according to current knowledge those of Chelobasis perplexa and Alurnus humeralis, which take almost one and more than one year from egg to adult.

Intracellular symbionts seem to play some role in the development of cassidine eggs and/or larvae. Maybe the relationship between the beetles and these bacteria is only commensalism rather than anactual symbiosis, given that no studies have been performed; all that can be said at present is that females and larvae have mycetomes in which cells infected by the presumed symbiotes occur. In the female, the mycetomes shed cells into the oviduct, where they are transferred to the eggs.

Host plants
As regards host plant specificity, there are still considerable gaps in our knowledge, but some patterns are already apparent. Predominantly utilized are commelinid monocots from order Arecales, Poales (especially Cyperaceae and Poaceae) and Zingiberales (especially Heliconiaceae and Zingiberaceae, and to a somewhat lesser extent Costaceae and Musaceae); the Commelinaceae themselves only play a minor role, as do other monocots. A large amount of eudicot host plant diversity is comprised by asterids. First and foremost, the Asteraceae, Convolvulaceae and Verbenaceae are utilized by many Cassidinae lineages. Rosids and Caryophyllales are eaten to a lesser extent, with only the Fabaceae and Lamiaceae of the former and the Amaranthaceae of the latter being widely found as tortoise beetle foodplants.

Among more basal angiosperms, magnoliids of the Aristolochiaceae and Piperaceae (Piperales), Annonaceae (Magnoliales) and Lauraceae (Laurales) have been recorded as host plants. But the former two are only eaten by Chalepini, which though a decidedly polyphagous lineage are not yet known from euasterids but feed on a number of plant families that are not otherwise recorded as Cassidinae food. The latter two are utilized by the Uroplatini, which are less unusual polyphages, though eurosids I are more prominent in their diet than usual among Cassidinae. The only non-angiosperm family hitherto recorded as food plant of these beetles and their larvae are Ophioglossaceae ferns. These are used by some Cryptonychini, a group that otherwise forages almost exclusively on commelinids.

Many Cassidinae species are monophagous, specific to one host plant genus or even species. Though exception are not infrequent, host plant association is normally lineage-specific, with specific beetle genera feeding on a small range of plant families, genera or species. A few Alurnini, Imatidiini and Hemisphaerotini are noted for having adapted from monocots – their tribes' usual food – to feeding on Theobroma (cocoa) of the Malvaceae (one species each of former two tribes) and the Fabaceae Inga (the two shelter-building Imatidium mentioned above, of the latter tribe).

Relationship with humans
Many of the larger "tortoise beetles" are prized by beetle collectors. Their bizarre shapes, whose function is easily explained, makes them an attractive educational display in museums, and scientific beetle collections (which often grew out of private collections) are usually fairly well-stocked at least with the more spectacular lineages of this subfamily. This has in recent years enabled scientific studies of this group to be quite comprehensive, at least compared to the subfamily's enormous diversity.

As pests, Cassidinae are less significant than other leaf beetles. Still, some are of economic importance due to their destruction of crops by feeding and transmission of plant pathogens. Coelaenomenodera elaeidis, Hemisphaerota and Promecotheca for example are noted as palm pests, while Aspidimorpha species damage Sweet Potato (Ipomoea batatas) crops. Other species may damaging to Poaceae such as rice (Oryza). Historically, in the 1930s Craspedonta leayana was responsible for the failure of a Malay Beechwood (Gmelina arborea)-based pulpwood industry to become established in Myanmar.

For pest control on large host plants, injections of thiocyclam hydrogen oxalate in root soil or stem can be used. As regards biological pest control, the sac fungus Beauveria globulifera as well as (against Promecotheca) the chalcid wasp Pediobius parvulus have been used with success.

Use in biocontrol
A more helpful aspect of cassidine phytophagy is their use as biocontrol of invasive weeds. In North America, Cassida azurea and C. hemisphaerica in the control of Silene cucubalus, Chelymorpha cassidea, Chirida guttata and Metriona bicolor to control the bindweeds Calystegia specium [check] and Convolvulus arvensis (Field Bindweed), and Stolas phaeopada against Mulefat (Baccharis salicifolia) have been successfully employed. Anacassis species have also proven useful in the control of Baccharis, and in New Zealand and North America, the Thistle Tortoise Beetle (Cassida rubiginosa) has been deployed against Creeping Thistle (Cirsium arvense).

Physonota species were used to control manjack (Cordia); namely, Physonota alutacea was used against Cordia macrostachya on Mauritius. In South Africa, Gratiana species were used against Solanum sisybriifolium. Introductions of weed biocontrol Cassidinae to Australia have been rather unsuccessful for reasons insufficiently known; the attempts to control Bitou Bush (Chrysanthemoides monilifera) with a Cassida from South Africa and Eastern Baccharis (B. halimifolia) with Stolas fuscata and S. phaeopada from Brazil failed because the beetles did not thrive.

Most importantly, Cassidinae fare better than most other biocontrol herbivores in stemming the expansion of the notorious shrub verbenas (Lantana), which affects many regions in Africa and the Pacific today. But even so, success in eradicating these vigorous plants which are spread by birds feeding on the fruit is by no means guaranteed. In any case, species that were used in Lantana biocontrol are Octooma championi, O. scabripennis, Uroplata girardi and U. lantanae.

Tribes
43 tribes of Cassidinae were recognized in recent times. How many of these are indeed valid monophyletic groups is not yet resolved. The "true" tortoise beetles in tribe Cassidini make up the largest of the groups known to be monophyletic. The Hispini are another large and monophyletic lineage of Cassidinae. While the Stolaini and Uroplatini are additional large tribes of this subfamily, their monophyly or at least their circumscription as monophyletic groups is not completely resolved.

More than half the proposed tribes, however, have a small or very small number of species, and this creates a considerable need for further research on their affinities – whether they do indeed represent distinct and possibly very basal lineages, or whether they are just specialized offshoots of a larger tribe and would better be included therein. Even some of the mid-sized tribes were not yet studied thoroughly in recent times. It is almost certain that some tribes will need to be abolished. For example the proposed "Mesomphaliini" have turned out to be invalid, as they unite the Eugenysini (a valid tribe) and the "Stolaini" (yet another paraphyletic assemblage).


 * Alurnini
 * Anisoderini m
 * Aproidini m
 * Arescini
 * Aspidimorphini
 * Asterzini
 * Basiprionotini
 * Basiptini
 * Botryonopini
 * Callispini
 * Callohispini
 * Cassidini m
 * Cephaloleiini
 * Chalepini
 * Charidotini
 * Coelaenomenoderini
 * Cryptonychini
 * Delocraniini m
 * Dorynotini m
 * Epistictini
 * Eugenysini m


 * Eurispini
 * Exothispini
 * Goniocheniini
 * Gonophorini
 * Hemisphaerotini m
 * Hispini m
 * Hispoleptini
 * Hybosispini
 * Imatidiini
 * Ischyrosonychini
 * Leptispini
 * Notosacanthini m
 * Oediopalpini
 * Omocerini m
 * Oncocephalini
 * Physonotini
 * Promecothecini
 * Prosopodontini
 * Sceloenoplini
 * Spilophorini m
 * Uroplatini