Leaf Beetles (lat. Chrysomelidae)

Description

Imago (adult form) of leaf beetles are small to medium-sized, with most species ranging from 1 to 18 mm (0.039 to 0.709 in) in length, excluding appendages, with just a few larger species such as Alurnus humeralis, which reaches 35 mm (1.4 in). The bodies of most species tend to be dome-shaped, and oval in dorsal view (though some species are more rounded or elongated), and they often possess a metallic luster or multiple colors. In most specimens, the antennae are notably shorter than head, thorax, and abdomen, i.e. not more than half their combined length. The second antennal segment is of normal size (which differentiates leaf beetles from the closely related longhorn beetles of family Cerambycidae). In most species, the antennal segments are of a more or less equal shape, at most they gradually widen towards the tip, although some Galerucinae in particular have modified segments, mainly in males. The first segment of the antenna in most cases is larger than the following ones. The pronotum of leaf beetles varies between species. In most, it is slightly to highly domed and trapezoidal to rounded-squarish in dorsal view. In some subfamilies such as the Cassidinae and to a lesser extent the Cryptocephalinae, the head is covered by the pronotum and thus not visible from above. The first three sternites are not fused, instead being linked by mobile sutures. Most species possess wings, although the level of development and thus flight ability varies widely, including within a single species, and some are flightless with fused elytra. The tarsal formula of leaf beetles may be helpful in identifying them; the tarsal formula may appear to be 4-4-4, but is actually 5-5-5 as the fourth tarsal segment is very small and hidden by the third. As with many taxa, no single character defines Chrysomelidae; instead, the family is delineated by a set of characters. Some lineages are only distinguished with difficulty from the closely related longhorn beetles, namely by the antennae not arising from frontal tubercles. Members of former chrysomelid subfamilies (Orsodacnidae and Megalopodidae) are also difficult to differentiate from true chrysomelids.

Diet

Chrysomelidae in general are herbivorous. Adults mostly feed on leaves and flowers of angiosperm plants, while larval diets are diverse.

Bruchinae larvae are seed-borers, usually in seeds of legumes. Many adults feed on pollen, not necessarily the same species as that of the larval host. Some do not feed as adults. Cassidinae larvae may be leaf minerss (many of the former Hispinae), stemborers (e.g. Estigmena) and external leaf feeders (e.g. Leptispa, Oediopalpa). Chrysomelinae generally feed on leaves as adults and larvae, though some species feed on flowers instead. Criocerinae larvae are usually leaf miners or feed externally on leaves. Some species are gallers instead. Eumolpinae larvae feed on roots. Most Cryptocephalinae larvae live and feed in leaf litter, making them detritivoress, while a few feed on green leaves. Some Cryptocephalinae have larvae that live in ant nests (myrmecophily), where they feed on dead plant or even dead animal matter. The semi-aquatic Donaciinae have larvae feeding on sap from the roots of aquatic plants. In addition to food, they also obtain oxygen this way, from the plant’s intercellular spaces. Adults feed on leaves of aquatic plants. Galerucinae are quite varied, with larvae living in soil and feeding on rootlets (e.g. Aulacophora, Cerotoma, Diabrotica), mining leaves (some Monoxia) or feeding externally on plants (e.g. Arima, Galeruca, Galerucella). Lamprosomatinae larvae feed on green plant parts or graze on bark. Sagrinae larvae mostly form galls in stems of shrubs, though Mecynodera balyi instead feeds inside seed pods of Pandorea vines. Adults feed on pollen. Spilopyrinae larvae are external leaf feeders. Synetinae larvae feed on roots, mainly of trees in cold northern forests. To be able to digest the plant matter, the beetles use enzymes such as pectinases. This group of enzymes are either produced by the beetles themselves, due to horizontal gene transfer, or symbiotic bacteria provides them with the enzymes. Both methods do not occur within the same species; they are never used simultaneously.

External links

Chyrsomelidae of northwest Europe List of subfamilies of European Chrysomelidae from University of Wrocław Brisbane leaf beetles Keys to the British genera and species of Chrysomelidae Chrysomelidae @ MIZA Archived 2020-10-24 at the Wayback Machine