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Alder Leaf Beetle

Agelastica alni

Alder Leaf Beetle

An Agelastica alni insect on a green leaf
Agelastica alni seite by Fabelfroh (CC-BY-SA-3.0)
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The Alder Leaf Beetle is a small, metallic blue insect, which can be seen in open, sunny areas in wetlands, typically alder carr. Throughout this time, they will feed mainly on Alder leaves but they're known to eat Beech, Hazel and Hornbeam, too. They're not severe pests, with plants tolerating most damage. Typical symptoms include holes in the leaves, which is purely aesthetic. Young trees may be more vulnerable to stunted growth, so picking off insects by hand (where appropriate) is advised at first.

Traits

Most trees recover from leaf beetle infestations.
Both adult beetles and larvae eat the leaves of alder.

Appearance

Adults: Beetles are around half a centimetre. They are metallic blue or black. They're similar to other metallic blue beetles, however, this species has a strong association for Alder, Hornbeam and Hazel. Larvae: Small grub-like caterpillars, black-grey and approximately 1 cm. Eggs: Small, yellow and laid in clusters.

Symptoms

They will leave holes in tree leaves following feeding.

Activity

Diurnal

Personality

Order

Coleoptera

Family

Chrysomelidae

Metamorphosis

Complete

Distribution

Europe and America

Biological treatment

It can be challenging to get rid of these beetles completely, especially if the trees infested are tall. Healthy and established trees can tolerate leaf beetle damage. If you have young trees, try removing beetles by hand at first. Birds are key predators of beetles and larvae. They can be attracted to gardens using bird tables, baths and other perches.

Chemical treatment

Organic insecticides containing natural pyrethrins can be used. It will need to be applied a few times to give good control. Other, more persistent pesticides are available, but it's recommended to consult with your local garden centre first before purchasing.

Attracts

Alder

Alnus spp.

Hazel

Corylus spp.

Hornbeam

Carpinus spp.

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