Xanthogaleruca luteola
Encyclopedia
Xanthogaleruca luteola, commonly known as the Elm Leaf Beetle, is a serious pest of the elm
. Indigenous to Europe
, it was accidentally introduced to North America
. Both the imagines
and larva
e feed on the emergent leaves of the elm. Repeated heavy infestation rarely kills the tree outright, rather it usually weakens it, rendering it vulnerable to attack by other insects and diseases. However, the beetle does not transmit Dutch elm disease
.
is 6–8 mm in length, ranges from yellow to green in colour, with a spot on its head, an hourglass mark and two spots on the pronotum, and a broad, dark stripe along the edge of each elytron
. The larvae are usually black, occasionally black and yellow, and < 13 mm long. The pupae are orange-yellow with black chaeta
e. The ova are yellow, and laid in spindle-like clusters of < 25 on the undersides of the elm leaves http://www.mortonarb.org/res/CLINIC_pests_ElmLeafBeetle.pdf.
Insecticide sprays are of little use since by the time the infestation is apparent, the application will be too late to be effective. However, tree trunks banded with insecticides can limit repetition the following year by killing the larvae as they descend before hibernation.
Elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...
. Indigenous to Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, it was accidentally introduced to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Both the imagines
Imago
In biology, the imago is the last stage of development of an insect, after the last ecdysis of an incomplete metamorphosis, or after emergence from the pupa where the metamorphosis is complete...
and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e feed on the emergent leaves of the elm. Repeated heavy infestation rarely kills the tree outright, rather it usually weakens it, rendering it vulnerable to attack by other insects and diseases. However, the beetle does not transmit Dutch elm disease
Dutch elm disease
Dutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...
.
Description
The imagoImago
In biology, the imago is the last stage of development of an insect, after the last ecdysis of an incomplete metamorphosis, or after emergence from the pupa where the metamorphosis is complete...
is 6–8 mm in length, ranges from yellow to green in colour, with a spot on its head, an hourglass mark and two spots on the pronotum, and a broad, dark stripe along the edge of each elytron
Elytron
An elytron is a modified, hardened forewing of certain insect orders, notably beetles and a few of the true bugs ; in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous...
. The larvae are usually black, occasionally black and yellow, and < 13 mm long. The pupae are orange-yellow with black chaeta
Chaeta
A chaeta or cheta is a chitinous bristle or seta found on an insect, arthropod or annelid worms such as the earthworm, although the term is also frequently used to describe similar structures in other invertebrates. The plural form is chaetae or chetae.In the Polychaeta, they are located on the...
e. The ova are yellow, and laid in spindle-like clusters of < 25 on the undersides of the elm leaves http://www.mortonarb.org/res/CLINIC_pests_ElmLeafBeetle.pdf.
Ecology
The imagines depart their hibernation sites (often houses) in early spring, the females laying their ova on the underside of the elm leaves. The ova hatch after one week, the larvae immediately feeding on the undersides of the leaves. This larval stage lasts for a period of between two and three weeks, at the end of which it will migrate to the lower part of the tree in search of bark crevices in which to pupate. The next generation emerges in mid-summer after two to three weeks' pupation, and begins feeding on the leaves. The female can lay < 800 ova, but this ovipositing may be interrupted by shortening of the photoperiod to < 14 hours, inducing a brief feeding bout before the search for a hibernation site.Symptoms
The larval feeding pattern leaves the upper surface and veins of the leaf intact, but causes it to wither and fall. The feeding imagines create small irregular but discrete holes in the leaves, and are generally less destructive than their offspring.Controls
In North America, there are few natural enemies, but in Europe, the ova of the beetle are often heavily predated by the chalcidoid wasp Oomyzus gallerucae .Insecticide sprays are of little use since by the time the infestation is apparent, the application will be too late to be effective. However, tree trunks banded with insecticides can limit repetition the following year by killing the larvae as they descend before hibernation.