Cassidinae | uk beetles

CASSIDINAE Gyllenhal, 1813

Tortoise Beetles

Includes two common species mostly associated with thistles, as well as a number of polyphagous species which can be found by general sweeping.

Introduction

After Alticinae this is the second largest group of leaf beetles, it is a little larger than the Galerucinae but many more species of all groups await description, it currently includes about 7200 described species (estimates vary) in about 2000 genera, which accounts for about 16% of the family total, and up to 43 tribes; the classification is far from settled and some groups formerly considered as separate subfamilies e.g. Hispinae Gyllenhal, 1813 are now included as tribes, many of the long-standing tribes do not appear to be monophyletic and many examples of species or genera being transferred between tribes and other groupings will be found in the literature. The present large size of the group is the result of a recent (2002) combining of the subfamilies Cassidinae (which formerly included about 3000 species of about 160 genera and up to 19 tribes) and Hispinae (with about 3000 species in 170 genera and 24 tribes), both described by Gyllenhal in 1813 in the same paper but the former a few pages before the latter, and both generally regarded as distinct until recently (although the latter group is still recognized by some workers). The subfamily is almost cosmopolitan with by far the greatest diversity in tropical and sub tropical regions, especially in the Neotropical region, and with the exception of Eurasia which is relatively very diverse, comparatively poor faunas exist in both northern and southern temperate regions e.g. about 120 species of 33 genera and 5 tribes occur in North America while more than 2000 species occur in the Neotropical region, the European fauna includes about 65 species of 4 genera in the tribe Cassidini Stephens, 1831 and four genera, each with a single species, of the Hispini Gyllenhal, 1813.

Description

The subfamily is distinguished among the wider Chrysomelidae Latreille, 1802 by three general features (synapomorphies). Firstly the antennae are placed close together and are inserted ventrally towards the front of the head, a condition most closely approached in the Galerucinae Latreille, 1802 where they are inserted laterally on the front margin, in most other subfamilies they are widely separated and placed laterally, either towards or on the front of the head. Secondly, the mouth is oriented ventrally, in other subfamilies it is oriented anterior or anteroventrally, and thirdly the fourth tarsomere has been lost completely whereas in other subfamilies it

POLYPHAGA Emery, 1886

CHRYSOMELIDAE Latreille, 1802

3.5-10mm

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is reduced. The distinction between tribes is often subtle and the present state is very unsatisfactory, there has been much overlap in the past and this is very likely to continue as new species are described and research continues, more especially with molecular techniques. Regarding the general groupings of Cassidinae and Hispinae, they have historically been separated on larval habits and general adult morphology but there are no strict morphological boundaries because among the numerous taxa there are always examples that display intermediate features, both in adult and early stage morphology as well as ecological and behavioural features but a few generalizations are possible as follows. Members of the ‘cassidine’ group of tribes have a rounded outline, many are vividly coloured and/or patterned and some can change colour due to their sub cuticle chemistry, their larvae live on the surface of stems and leaves and feed on the outer layers and most cover themselves with a mixture of secretions, frass and plant material-so called faecal shields-that render them cryptic and are thought to provide a chemical defence against predators and parasites although this defensive role has yet to be demonstrated. Members of most of the ‘hispine’ tribes are elongate, rather parallel-sided and somewhat flattened beetles, they often have strongly punctured elytra and many have spines either along the lateral margins or across the dorsal surface, and the larvae of most species are stem or leaf miners, giving rise to the common names of hispines or leaf-mining beetles. The morphological diversity of both groups is very wide, hence the large number of tribes, and can only be appreciated with an awareness of the isolating features given above and by reviewing pictures of a good selection of fauna from around the world, a simple thing to do online, but the following notes are provided as a very brief overview of these two major groupings.

'Hispinae Gyllenhal, 1813'

The hispine group of tribes occur almost worldwide but are very poorly represented in temperate regions and thus far no species have been found in New Zealand, the tribes form their own groups and there is generally little overlap between the faunas of the Old-World and those of the New World. Many of the species, genera and tribes, especially in some tropical regions, are badly in need of revision and the biology is known, but sometimes in only the most general of terms, for about 6% of the species and many of these are either plant pests or from countries with better understood faunas. An interesting feature found in several Old-World and New-World genera, and of at least 10 tribes, is the presence of stridulatory organs on the head and anterior prothoracic margins, these may be present in both sexes or only in the male, The general morphology can be summed up as follows (although doing no justice to the group at all). They vary in size from 2 to about 40mm in length and in shape from elongate, narrow and parallel-sided, which applies to the majority of species, to broadly oval with some approaching the general habitus of cassidine species, and from flat to highly convex dorsally; the elongate form is probably most extreme in some African species e.g. Eurispa vittata Baly, 1858 which superficially resembles an elongate and narrow elaterid or a Lixus weevil-the elytral apices are even separately acuminate as in some members of that genus. Colour and pattern vary widely, there are many drab black or brown species and many unicoloured green, yellow or red species, but many are strikingly patterned with longitudinal or transverse bands or fascia of contrasting bright reds, yellows, greens or violets but blue colours are comparatively rare. The dorsal cuticle is usually punctured and often striate or rugose and many species are either mostly glabrous or only very finely and sparsely pubescent. The head is generally small and substantially visible from above although it may be hidden beneath an explanate anterior pronotal margin, the eyes are well-developed, broadly transverse and only moderately convex, the antennae are inserted on the frons between the eyes and usually have 11 segments although some or even most may be fused; in extreme cases there are only 3 distinct antennomeres, and in some the basal segments are produced into

Hispa atra Linnaeus, 1767

long spines or the terminal segments are fused to form a club. The frons and clypeus are angled down posteriorly and the mouthparts are situated in a circular cavity which is sometimes covered by the anterior margin of the prosternum. The pronotum is very variable; usually transverse to quadrate, often broadest across the base and narrowed to a straight anterior margin but may be rounded laterally and lack distinct angles, there is usually a distinct lateral border and there may or may not be trichobothria inside the angles, the surface is often simply flat to convex and usually distinctly punctured and/or sculptured with tubercles, ridges or furrows, but a feature of many species are series of robust dorsal and/or lateral spines, these may be arranged simply, as in the European Hispa atra Linnaeus, 1767 where they are arranged singly or in pairs around the lateral and anterior margins, or they may form complex arrangements in some tropical species where they are very long and mounted in pairs or small groups on widely explanate portions of the lateral margins. Extremely developed explanate pronotal and elytral margins are a feature of several exotic groups, they often have toothed or spiny margins and may be strongly punctured or otherwise sculptured, in extreme cases the punctures are expanded and penetrate the cuticle, forming longitudinal series of translucent ‘windows’ parallel to the lateral margin, a condition superbly demonstrated in the Old-World genus Cassidispa Gestro, 1899. The elytra are similarly very variable, there are often 8 to 10 regular striae and an abbreviated scutellary striole which may be finely or very strongly punctured but they may be missing altogether or modified with tubercles or ridges etc,. The interstices may be simple and flat or convex or modified into longitudinal series of spines or tubercles, sometimes alternate interstices may be raised and the strial punctures transverse, giving a strong impression of certain lycids. The basal margins may be separately curved, and sometimes very strongly so, or otherwise modified but rarely simply straight, the lateral margins are often sinuate about the middle or variously explanate, serrate, dentate or furnished with tubercles or spines, and the apical margin may be continuously or separately rounded but in some tropical species it is truncate, in extreme forms the apical quarter is dilated before a truncate apical margin and the angle produced into a spine. Hispine larvae are also very variable, from one to about 40mm when fully grown, elongate to rounded in shape and, like the adults, many are equipped with strong defensive spines to the various body segments, some of these are very spectacular but as descriptions have been published for only about 6% of species there are no doubt many surprises in store. Most are pale coloured, white, creamy, yellow or green, no doubt to make them cryptic within the host material; they mine leaves or stems or develop among fruits or flower parts, and so far as is known, only a few are free-living. In general they are flattened and lack a caudal appendage on the terminal abdominal segment, the antennae are 3-segmented and the abdomen has 8 visible segments, each of which may have a long and robust lateral spine which is usually armed with smaller spines along its length, the legs are short but robust and the head and sometimes various dorsal plates to the thorax and elytra are well-sclerotized although in some tribes the legs are short, almost vestigial, and the head is entirely ventral and hidden from above by the thorax. A well-developed caudal process is present in larvae of the tribes formerly included within Cassidinae s.str. and this is used to hold a faecal shield above the body for protection, but while this process is absent in the present group of tribes there are a few species e.g. the Neotropical Odiopalpa negligens (Weise, 1905) (Spilophorini Chapuis, 1875) with free-living larvae that carry a shield.

Although many species are polyphagous and some feed on a range of plants of widely different families, the majority are oligophagous or monophagous at the generic level and adults tend to be more polyphagous than their larvae, the majority feed on monocotyledonous plants and a wide range of families have been recorded as hosts including Orchidaceae, Pandanaceae, Musaceae, Cyperaceae, Poaceae, Arecaceae and Zingiberaceae. Rather less diversity has been recorded for dicotyledonous host families but these include Malvaceae, Asteraceae, Fabaceae and Pandanaceae, and the expansion from monocots to dicots is thought to be a recent evolutionary shift. A wide range of feeding behaviours is seen among the various tribes but the majority of species (more than 2500 among 22 tribes) are leaf-miners, the various species produce characteristic mines and all patterns are found, from linear or meandering mines to extensive blotch mines. Free-living larvae feeding openly on the leaf surface are rare and known from only 2 genera in separate tribes. Stem-borers are known from 4 genera of 2 tribes and a specialized type of feeding sometimes called ‘bract scraping’ is known from 2 genera of 2 tribes. True leaf-rollers are known from 13 genera of 2 tribes and a few species of a further 2 tribes construct leaf-shelters in which they feed. Many species have adopted commercially grown plants and crops as hosts and in tropical areas some have become serious economic pests, the majority are Old-World species of Africa and southern Asia and, of course, they are readily transported between countries and regions, crops most commonly affected include soybean, rice, sugarcane, bamboo, palms and a range of spices, particularly ginger.

Only 4 species representing 4 genera occur in Europe and all are classified in Hispini, 3 of these are restricted to warmer Mediterranean areas and Hispa atra Linnaeus, 1767 is the only widespread species, it is locally common throughout Europe north to Denmark and Belarus and extends east Russia and Asia Minor to Mongolia and China but does not occur in the UK. Its biology is typical of the tribe; it occurs on dry grassland and pasture is oligophagous on various grasses (Poaceae) with larvae mining longitudinal galleries along the leaves and pupation occurring within the mine.

'Cassidinae Gyllenhal, 1813'

The cassidine group of tribes are commonly known as tortoise beetles and this is understandable when considering the rounded and flattened species that occur almost worldwide and constitute the entire fauna of northern temperate regions, but rather less so when some of the amazing tropical diversity is considered. Including only 12 tribes (in a modern sense) and lacking the range of morphological diversity seen in the previous group of tribes, it is nonetheless very diverse. As with the hispine group the tribes are confined to various regions of the Old and New worlds and diversity is greatest in the Neotropical zone: Aspidimorphini Chapuis, 1875 (7 genera, >280 spp. Asia and Africa), Basiprionotini Gressis, 1952 (5 genera, about 80 spp. Asia, Philippines, Madagascar) Cassidiini Gyllenhal, 1813 (76 genera, >960 spp. Almost worldwide), Notosacanthini Hincks, 1952 (2 genera, >250 spp. Old World, widespread except Europe), and the following tribes are restricted to the Neotropical region, Delocraniini Spaeth, 1929 (1 genus, 3 spp.), Dorynotini Monrós & Viana, 1949 (6 genera, about 50 spp.), Eugenysini Hincks, 1952 (3 genera, 35 spp.), Gomiocheniini Spaeth, 1942 (5 genera, 30 spp.), Hemisphaerotini Monrós & Viana, 1951 (2 genera, >40 spp.), Mesomphaliini Hope, 1840 (24 genera, about 700 spp.), Omocerini Hincks, 1952 (7 genera, about 150 spp.) and Physonotini Hincks, 1952 (7 genera, about 50 spp.). Many species within these tribes are morphologically rather similar and most will be recognized as tortoise beetles but many grossly-developed species occur in tropical regions worldwide, these modifications are generally exhibited by the extent of the explanate lateral margins and the convexity of the pronotum and elytra. Colouration is a very variable feature; in the simplest case the entire dorsal surface is green, yellow or red with various dark spots or streaks, often along the sutural and basal elytral margins, and a common feature is longitudinal contrasting metallic bands on the elytra. Exotic species can be very different; they may be entirely brilliant metallic green, red or blue or dark, in some cases black, with patches of metallic green etc, some are densely mottled with dark flecks of colour and concentric rings of contrasting colour are seen in some species-so-called ‘bulls eye’ or ‘target’ beetles, in many the explanate margins are transparent or coloured differently to the rest of the elytra, this gives a very striking effect when the elytra are very broadly expanded but the pronotum is normal, and a common theme is a contrasting T-shaped pattern on an otherwise pale or transparent elytra. Some species exist in a range of colour morphs and some can change colour in response to external stimuli e.g. some green species may become pale yellow or brown when disturbed or kept in different environments, and many lose their colour after death, hence collections of green tortoise beetle species tend to be mostly shades of brown although colours can be preserved by keeping them in alcohol. Many general features of cassidine colouration may be seen in the North American Deloyala guttata (Olivier, 1790), but in general the northern temperate species are more soberly coloured. Cassidines vary widely in size and shape, from 2mm to more than 40mm long, and from elongate-oval to very broadly-oval and a feature of many exotic species is the broad elytral shoulders that may protrude laterally far beyond the pronotal base, most are rather flattened or with moderately ascending lateral margins but in warmer areas many are more convex and the pronotum and/or elytra may be strongly vaulted from an explanate margin and in extreme cases this vaulting is produced into an oblique or erect thorn-like spine, this is often coupled with a dilated elytral base and serrate lateral margin, giving the species a very strange appearance. Most species are glabrous or only sparsely pubescent although many, even in northern regions, have a fine and very short pubescence that needs to be viewed in strong oblique light to be appreciated, this can be seen in our UK species Cassida vibex Linnaeus, 1767. The head may be exposed between protruding anterior pronotal angles or hidden beneath a rounded pronotum, it is quadrate to elongate and flattened with the mouthparts ventral and oriented towards the prosternal margin, the eyes are large and occupy most of the margin when viewed from below and the vertex is usually dissected by a medial longitudinal suture, the antennae are 11-segmented (or with various segments fused in exotic species) and placed close together anteriorly between the eyes. Head structure varies widely due to the ventral orientation e.g. the frons and clypeus are usually fused with a distinct frontoclypeal suture visible from below, but in extreme cases both the frons and clypeus may be absent and the antennal insertions separated from the mouthparts by a narrow sclerite. In most there are distinct frontal sutures between the eyes, usually diverging ventrally from the antennal insertions, which often provide valuable features for identification. This evolutionary ventral shifting of the head has also produced a great variation in the structure of the mouthparts e.g. in many the mandibles are flattened and dilated with mesal rather than apical cutting edges. The pronotum varies from transverse to quadrate and from hemispherical to quadrangular with strongly produced anterior angles, the surface is variously convex and punctured and may have strong punctures, fovea or other surface structure, the lateral margins are variously explanate and may be bordered, toothed or otherwise modified, the basal margin is usually sinuate and often serrate or with isolated teeth. The prosternum is transverse or quadrate with elliptical and posteriorly closed coxal cavities separated by a broad and usually flat process that meets the mesosternum. Elytra variable, as above, but where the explanate margins are well-developed they are usually matched ventrally with very broad and almost flat epipleura which are usually punctured or sculptured similar to the dorsal surface. The shape varies from parallel-sided to strongly-rounded or variously dilated laterally or across the base and the apical margin is usually continuously-rounded and covers the abdomen by a wide margin, there are usually punctured striae but they may be obscured by the strength of the punctures or by various surface structures and they are often confused towards the base, in some exotic forms they may be very fine, incomplete or missing altogether, the interstices may be flat, convex or raised and they are often confused by elongate tubercles or other structures or sometimes obliterated by very strongly punctured striae. Most species have fully-developed hind wings and are capable of strong flight. Abdomen usually with 5 or 6 ventrites which are usually to some extent fused, the basal ventrite produced between the hind coxae to reach the metasternum and the terminal segment rounded, in females it is indented or depressed while in males it is smoothly convex. Legs long and robust but in normal setting only the coxae are visible beyond the explanate margins, all coxae narrowly separated, the middle coxae elliptical and the hind coxae transverse, trochanters small and obliquely attached to the femoral base, the femora are flattened and usually a little longer than the tibiae which are usually gradually broadened from the base to a truncate apex and lack terminal spines. The tarsi are always 4-segmented, usually with 1-3 bilobed and often strongly so and the fourth small and hidden within the lobes of the third. The claws are paired and usually separated from the base but connate claws are seen in some exotic groups, and in most they are simple or toothed at the base but bifid claws are unknown in the group. Larvae are very variable in form from elongate and cylindrical to oval and flattened, colour varies from entirely black to pale yellow or green, a common feature is one or several branched or spiny lateral projections on the thoracic or abdominal segments and all possess a caudal process which may be short and stout or long, whip-like, branched or paired, and many of these featured may remain in the pupa.

Adults occur on host foliage and may often be found by general sweeping as they disperse and may migrate between winter and summer habitats by flight, many species in warmer areas have been found swarming in large numbers before the breeding season and many species occur over a long season with adults overwintering and becoming active from early in the year. In general the life cycle is rapid, in temperate regions development from egg to adult takes 8 to 12 weeks while in warmer areas it is more rapid; between 4 and 8 weeks although a few species are noted for their protracted development which may last more than a year. Most species are univoltine with breeding occurring in spring and early summer. Eggs are laid singly or in batches on the underside of leaves, often in small protective cases but sometimes exposed and covered in a secretion by the female, and they usually hatch within a few days. Larvae feed on the chorion as they emerge and soon begin to consume host foliage, most species of Cassidini (and some other tribes) have five active and free-living instars and in some the fifth may become inactive, the ‘pre-pupal’ stage, but more generally cassidines are notable for the great variation in the number of instars which varies from 3 to 9 between tribes. Some exotic species exhibit parental care; eggs are laid in batches and larvae are gregarious, feeding and pupating together on the host plant with the female parent guarding them until the new adults emerge. More generally they roam exposed on the host foliage as they feed, each carrying a shield of cast skins, organic detritus and secretions on the caudal appendage (sometimes referred to as an ‘anal fork’) which can be moved and is thought to provide protection against predators and parasites. Pupation always occurs on the leaf or stem surface, usually on the ventral surface of leaves and usually covered or partly covered by the larval faecal shield.

In contrast to the hispine group of tribes, the majority of cassidines attack dicotyledons and the group includes fewer economic pest species although in warmer regions large populations or swarms occasionally occur and they may cause minor damage to crops or ornamental plants, they vary from widely polyphagous to oligophagous or, rarely, monophagous; a wide range of families include host species but in temperate regions many attack various Asteraceae, Convolvulaceae, Caryophyllaceae and Amaranthaceae.

Dorynota monoceros (Brazil)

UK species

The group is familiar to UK naturalists as it is represented by our 14 species of tortoise beetles; mostly members of the genus Cassida (meaning helmet in Latin) Linnaeus, 1758, which is a very widespread Old-World group of more than 430 species and is the largest genus in the subfamily; most occur in the tropics and of the 160 or so Palaearctic species, 57 occur in Europe and so they constitute the majority of the subfamily diversity in that region, only 5 species occur in North America and of these only one is indigenous. C. rubiginosa Müller, O.F., 1776 and C. vibex Linnaeus, 1767 are widespread and common across England and Wales while C. flaveola Thunberg, 1794 and C. viridis Linnaeus, 1758 are also widespread but more local. C. prasina Illiger, 1798 is widespread in England and Wales but generally scarce, and C. nobilis Linnaeus, 1758 and C. vittata de Villers, 1789 are widespread but scarce and mostly coastal. Our remaining species are very local and rare; C. denticollis Suffrian, 1844 is known from a few sites in Southern England and south west Scotland, C. sanguinosa Suffrian, 1844 is restricted to a few sites in the south and is also known from Southern Ireland, C. murraea Linnaeus, 1767 occurs mostly in the south-west and South Wales where it can be locally common, and C. nebulosa Linnaeus, 1758 is known from a few widely separated sites in the south, mostly from Norfolk and Hampshire. The very rare C. hemisphaerica Herbst. 1799 is known from the south east of England, the West Country, Wales and south-west Scotland but is otherwise generally absent. Of the 4 European species of Hypocassida Weise, 1893, only H. subferruginea (Schrank, 1776) is widespread and extends into central and northern areas, it is included in the UK list but was last recorded in the 19th century and is now thought to be long extinct. Pilemostoma fastuosa (Schaller, 1783) is a very widespread European species that extends north into Fennoscandia and the UK.