GALERUCINAE Latreille, 1802
Includes several very common species, many of which can become super-abundant when conditions are right.
This group has generally been considered as a tribe within a much larger and more broadly-defined Galerucinae which also included the Alticinae Newman, 1834 as a tribe, and as such it formed (perhaps arguably) the largest subfamily of the Chrysomelidae Latrielle, 1802 with about 15000 described species in more than 1100 genera; more than half of these (>8000 species) but slightly less than half of the genera were included in the Alticini. Galerucinae s.str. includes about 6500 described species within about 600 genera, and many more await description. Both subfamilies are morphologically very diverse and so most characters and combinations of characters overlap; in limited faunas such as our own there may be general differences in e.g. the form of the frontal furrows and tubercles and of the pronotal surface structure, and these can be used to separate the groups in the UK but this breaks down for the wider world fauna. The key character used to separate the subfamilies is the form of the hind femora; in the present subfamily it is unmodified but in Alticini it is enlarged to accommodate (usually, but there are exceptions such as Luperomorpha Weise, 1887, such is the present state of play with the classification) a femoral extensor tendon which allows the beetles to jump very powerfully in order to escape predators. There remain many problematic genera in both subfamilies and it is likely that taxonomic relationships will change in due course. The question of tribal classification within the Galerucinae is very difficult as many groups are defined upon combinations of characters that have been in use for many years, some appear to be natural groups while others are obviously not, and the present system, which variously includes eight tribes, will no doubt continue in use until further phylogenetic studies of the group as a whole are carried out. The UK fauna, which is outlined below, includes members of 3 tribes in the latest checklist.
The subfamily is cosmopolitan with the greatest diversity in tropical and subtropical regions while northern temperate regions are often poor in genera and species e.g. the American fauna includes about 220 species of 42 genera while that of Europe includes 116 species of 19 genera. The most diverse region is the Oriental with 186 genera and the adjacent eastern Palaearctic region is also very diverse, especially compared with Europe. About 175 genera, or a third of the total, occur in tropical Africa and more than 100 genera are Neotropical while the Australasian fauna includes about 60 genera. A striking feature of this distribution is the very high number of endemic genera in tropical Africa (148 or 85%, of which 31 are endemic to Madagascar), for all other regions the figure is <50%. Inevitably some species have been transported across the world with the trade in plants and food e.g. Diabrotica virgifera LeConte, 1868, the ‘western corn rootworm’ is established in Europe and occasionally occurs in the UK, but Diabrotica Chevrolat, 1836, with about 370 species, is otherwise a widespread New World genus. There are no cosmopolitan genera but some come close e.g. Luperus Geoffroy, 1762, which includes almost 100 species, occurs worldwide with the exception of Australasia. Other large genera tend to be either Old-World or New World in distribution; the largest genus, Monolepta Chevrolat, 1836, with more than 700 species or just over 10% of the subfamily total, occurs throughout the Old World although does not extend into Europe. Calomicrus Dillwyn, 1829 is a widespread Old World genus of about 85 species, it is absent from Australasia but the European fauna is relatively rich with 18 species of which the widespread C. circumfusus (Marsham. 1802) extends to the UK, Apophylia Thomson, 1858, with about 140 species, is also widespread and does extend into Australasia but is absent from Europe. Oides Weber, 1801 (>160 species) and Aulacophora Chevrolat, 1836 (>170 species) occur throughout the Old World but of these only 3 species of the latter occur in Europe. Several larger genera are widespread in the New World e.g. Acalymma Barber, 1880(>70 species) while others e.g. Neobrotica Jacoby, 1887 are confined to the Neotropical region. An example of an Australasian endemic genus is Adoxia Broun, 1880 with 62 species. The UK fauna is relatively tiny with 20 species of 8 genera and is mostly an extension of the European fauna with no endemic species.
Adults feed externally on the foliage of a very wide range of plants, most are monophagous or oligophagous although many have preferred hosts and will switch to others if necessary. The vast majority of hosts are angiosperms and more than half are dicotyledons, a small proportion have been recorded from Bryophytes, Horsetails, Gymnosperms and ferns, and many have been observed feeding on pollen and nectar of a wide range of flowers. The larvae of many species of Luperini feed on roots although the adults may prefer different host plants. Typically, eggs are laid in small batches or singly on stems or foliage where the larvae will feed, some species insert eggs into stems or fruits and some oviposit in the soil below the hosts and species of Galeruca attach an egg case low down on the host. Larvae generally feed openly on foliage or within stem or leaf mines and pupate in a subterranean cell. The majority of adults feed on foliage although a few also consume pollen or nectar, they often feed on the parenchyma or mesophyll and so produce translucent patches but otherwise leave the leaf intact; some, such as the European Pyrrhalta viburni (Paykull, 1799), may occur in large numbers with both adults and larvae feeding together and extensively skeletonising whole areas of host foliage. Some exotic species e.g. the Nearctic Diabrotica virgifera and D. barberi R. Smith & Lawrence, 1967, have become very serious pests of agricultural crops. They will be found in almost all habitats from wetlands, including on aquatic vegetation, to deserts and from maritime to alpine regions, and most are good fliers and quick to colonize new areas. In temperate regions development generally proceeds through the spring and summer with new generation adults occurring from mid-summer, these will either substantially die-off after reproducing or overwinter and reproduce in the spring, in the former case it is often the eggs that overwinter although at least some adults will normally survive until the following spring.
Members of the Galerucini vary in length from 2-20mm but most are 4-8mm, the shape is very variable but most are elongate with the pronotal base narrower than the elytra across the shoulders, and most are rather characteristically widened towards the apex, very convex to flattened dorsally and weakly convex underneath. Many are glabrous above but some are finely and densely pubescent. Head mostly exposed, prognathous or weakly inclined, vertex and frons convex and with a longitudinal impression, frontal tubercles present but variously developed, sometimes very weakly so, and delimited posteriorly by a transverse impression. A frontoclypeal suture may be present, sometimes very faint or well-impressed, and the clypeus is generally triangular and sometimes emarginate anteriorly. Eyes round to weakly oval, finely faceted and sometimes pubescent. Antennae 11-segmented and filiform, weakly serrate or, rarely, clubbed, inserted close together anterior to or between the eyes, usually on well-defined tubercles. In some species they are sexually dimorphic. Mandibles short and broad, smooth or toothed internally and simple to bi- or multi-dentate apically. Terminal segment of all palps cylindrical and narrowed to a rounded or truncate apex. Pronotum quadrate to quite strongly transverse, lateral margins simply rounded to straight or variously toothed to excavate and not, or only weakly, explanate. Angles generally distinct and often toothed and almost always with a setiferous puncture. Surface smooth and finely to coarsely punctured to strongly sculptured but usually without the distinct transverse impression or basal fovea seen in many Alticini. Prosternum short and flat or convex in front of open or closed coxal cavities, coxae transverse, sometimes strongly so, and touching or very narrowly separated, the process varies from incomplete to long, extending behind the coxae, the form is very variable. Meso-coxae round to very slightly transverse and generally contiguous. Meta-coxae contiguous or nearly so and transverse but not extending to the elytral margin. Abdomen with 5 free ventrites, the first longer than the second and without post-coxal lines. Tergites 9 and 10 completely fused in the male. Scutellum visible, triangular to elongate and acute to rounded. Elytra elongate, rounded to almost parallel-sided, discontinuous with and wider than the pronotum, generally completely covering the abdomen and continuously rounded, sometimes separately so or obliquely truncate, and usually have a single sensilla patch. Epipleura variable but generally broad below the shoulders and narrowed or absent beyond the middle. The surface may be smooth or with very fine to very strong punctation, often random but sometimes forming striae and species of many genera have distinct longitudinal carinae. Legs well-developed, often robust, and usually finely pubescent. Pro-coxae conical and prominent, often touching at the middle, meso-coxae globular, meta-coxae transverse and usually flat. Femora only moderately thickened, the meta-femora usually a little wider than the others, tibiae slender and unadorned, generally thickened towards the apex. Tarsi 5-segmented; the third strongly bilobed and the fourth tiny, 1-3 ventrally with dense adhesive setae. Claws free and simple, bifid or appendiculate. It is probably fair to say that in general members of the Galerucinae are less gaudy and metallic than other chrysomelid groups, especially in temperate regions where many are drab, black to various shades of brown or brown with darker markings but there are many brightly coloured or aposematic species in warmer parts of the world e.g. some Neotropical Diabrotica Dejean, 1836, such as the Old-World pumpkin beetle, Aulacophora hilaris (Boisduval, 1835), or the New-World Phyllobrotica physostegiae E. Riley, 1979, which is worth looking at for it’s unusual antennae which are serrate with the basal segment enlarged, as well as the striking black and orange colour.
Our UK species are typical of the northern temperate fauna and much of the world fauna as a whole because species tend to be rather typical, differing mostly in colour and fine detail. They are currently included in 3 tribes. Our fauna includes 2 established introductions; Diabrotica virgifera (Luperini, Diabroticina) which occurs very locally in the southeast, and Luperomorpha xanthodera (Fairmaire, 1888) (of uncertain placement in the tribal system) originally from China, which has recently become established on cultivated roses in garden centres. Two of our species are included in the Hylaspini Chaupuis, 1875; Agelastica alni (Linnaeus, 1758), formerly considered extinct but recently spreading and becoming common on alders, and Sermylassa halensis (Linnaeus, 1767) which is widespread and locally common throughout England and Wales. Luperini includes 5 UK species in the subtribe Luperina Gistel, 1848. Calomicrus circumfusus (Marsham, 1802) is a very local species in England and Wales and is associated with gorse. The 2 UK species of Luperus Geoffroy, 1762 are associated with various broadleaved trees, both are widespread though local. Phyllobrotica quadrimaculata (Linnaeus, 1758) is very local and generally scarce; it is associated with skullcaps, Scutellaria spp. in southern England and Wales. Our remaining species are included in the Galerucini Latreille, 1802. Our 6 species of Galerucella Crotch, 1873 are associated with various herbaceous plants and all are widespread and locally common. Three species of Lochmaea Weise, 1883 are widespread and generally common; L. suturalis (Thomson, C.G., 1866) is associated with heather moorland, L. crataegi (Forster, 1771) with hawthorne and L. caprea (Linnaeus, 1758) with various willows although also develops on other broadleaved trees. Pyrrhalta viburni (Paykull, 1799) is widespread and common on various species of Viburnum, often occurring in numbers on ornamental plants in gardens etc.