Alder leaf beetle
The metallic blue alder leaf beetle (Agelastica alni) feeds on the leaves of alder trees. It has become common in parts of England and Wales since 2004.
Quick facts
Common name - Flea beetle
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Scientific name - Various, mainly Phyllotreta and Psylliodes species
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Plants affected - Many plants in the brassica family. Also nasturtium and Cleome
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Main symptoms - Small rounded holes in the foliage, especially on seedlings
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Most active - Spring and summer
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What are flea beetles?
There are more than 100 species of flea beetle in Britain, they are a subfamily of the leaf beetles (Chrysomelidae). Most do not feed on garden plants or have a noticeable effect on them, a few species in the genera Phyllotreta and Psylliodes feed on brassicas and related plants. The small beetles are 2-3 mm (about 1/10 in) long, with enlarged hind-legs that enable them to leap when disturbed. Adult beetles are coloured black or metallic green or blue, some have a yellow stripe running the length of each wing case. The adults feed on the leaves and the larvae on the roots, the root damage does not usually affect crops in gardens.
Symptoms
- Rounded holes are scalloped out of the upper leaf surface; often these do not go all the way through the leaf. The damaged areas dry up and turn pale brown
- are particularly susceptible, the growth of older plants is only checked if populations are large
- Adult flea beetles can be seen jumping off leaves when disturbed
- Root feeding by the grubs does not usually affect growth in home gardens
Management
Populations of this beetle can be tolerated, especially on larger brassicas where outer leaves are discarded. These beetles usually have a limited effect on edible parts.
- Encourage wildlife in the garden, such as birds , frogs and predatory ground beetles who will eat the larvae and sometimes the adult beetles
- Growing susceptible crops under insect proof mesh may keep the beetles out
Biology
Brassica flea beetles overwinter as adults in leaf litter, emerging in mid-spring to feed on brassica and other host plants. In late summer, significant migrations of adult beetles from brassica crops, such as oilseed rape fields, can damage mature plants in gardens. The larvae, which are whitish-brown, live in the soil and feed on plant roots, though this rarely causes significant damage in garden plants. Pupation occurs in the soil during mid-summer.
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