The insects of the beetlefamilyChrysomelidae 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 only some of them are listed below. The precise taxonomy and systematics are likely to change with ongoing research. Leaf beetles are partially recognizable by their tarsal formula, which appears 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 the Chrysomelidae; instead, the family is delineated by a set of characters. Some lineages are only distinguished with difficulty from longhorn beetles, namely by the antennae not arising from frontal tubercles. Adult and larval leaf beetles feed on all sorts of plant tissue, and all species are fully herbivorous. Many are serious pests of cultivated plants, for example the Colorado potato beetle, the asparagus beetle, the cereal leaf beetle, and various flea beetles, and a few act as vectors of plant diseases. Others are beneficial due to their use in biocontrol of invasive weeds. Some Chrysomelidae are conspicuously colored, typically in glossy yellow to red or metallic blue-green hues, and some have spectacularly bizarre shapes. Thus, they are highly popular among insect collectors.
Description
The imagos of leaf beetles are small to medium-sized, i.e. most species range from 1.0 to 18 mm in length, excluding appendages, with just a few larger species such as Alurnus humeralis, which reaches 35 mm. The bodies of most species are domed, and oval in dorsal view, 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. 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.
Until recently, the subfamily Bruchinae was considered a separate family, while two former subfamilies are presently considered families. Other commonly recognized subfamilies have recently been grouped with other subfamilies, usually reducing them to tribal rank.
Predators
Some species of wasps, such as Polistes carolina, have been known to prey upon Chrysomelidae larvae after the eggs are laid in flowers.
