Some have a wide host range, such as vine weevil. Others are specific to a single type of plant, such as water lily beetle. Viburnum beetle can be a serious pest but attacks just a few types. Lily and rosemary beetles, found as far north as Scotland, can cause serious leaf damage.
Extensive efforts continue to be made to keep Asian longhorn beetles out of the UK due to their significant threat to a range of broadleaved and fruit trees - such as maples, ash, horse chestnut, willow and pear - and the drastic measures needed for control. Natives of China and Korea, longhorn beetles have become established in parts of the USA. The notifiable pest has been intercepted on imported wood products, packaging and bonsai trees.
Growers should also keep an eye open for the distinctively striped Colorado beetle, a notifiable pest of potato crops that has been known to appear on imported nursery stock.
Flea beetles come in a range of shapes, sizes and colours, and can affect outdoor ornamentals. The large blue flea beetle (Altica lythri) can attack fuchsia, potentilla and oenothera. The turnip flea beetle (Phyllotreta cruciferae) will attack brassicas including Cheiranthus, Crambe, nasturtium and Matthiola.
How to recognise them
Adult viburnum beetles (Pyrrhalta viburni) are grey-brown and up to 6mm long. Larvae are cream-coloured with black markings.
The adult lily beetle (Lilioceris lilii) has a characteristic bright-red body. It is around 8mm long and has a black head and legs. Larvae, found on leaves and stems, are red-brown but camouflaged by black frass.
Adult rosemary beetles (Chrysolina americana) are 8mm long and have an attractive body of metallic green with purple stripes. They cannot fly. Larvae are off-white, with five darker lines lengthwise along the body.
Asian longhorn beetles (Anoplophora glabripennis and A. chinensis) are black and shiny with white spots on the wing cases and 20-35mm long. The long antennae are highly distinctive, with segments alternating black and white. Larvae can be as long as 50mm and cream in colour with a hard brown head. Both insects are EU-listed pests.
Adult viburnum beetles lay eggs in holes they make on the undersides of woody stems in late summer, covering them with a cap of chewed leaves. Larvae emerge in spring and feed on developing leaves from April to June before dropping to the ground to pupate. Adult beetles emerge to feed from July to September.
Lily beetles overwinter as adults and can be found from spring to autumn, when they lay orange-red eggs on host plants in small groups. Larvae tend to feed in groups and pupate in the soil. Only one generation is produced each year.
Rosemary beetles lay eggs on the undersides of leaves. Studies suggest adults lay eggs in late summer and on warmer winter days. Eggs hatch in two weeks. Larvae feed for three weeks before pupating in soil. Adults emerge after two-to-three weeks.
Asian longhorn beetles emerge from trees in May-August, or later depending on temperature, through round exit holes with sawdust at the entrance. Adults mate in the crown of trees and females lay eggs singly in cuts in the bark of branches. Larvae feed under the bark, tunnelling into heartwood as they grow. They overwinter as larvae or pupae.
Flea beetles can overwinter on weeds, emerging from May onwards. Eggs, laid singly or in groups, hatch in two-to-three weeks. Larvae feed on host plants and pupate in the ground.
Attacks by viburnum beetle are limited to Viburnum opulus, V. tinus and V. lantana but can be serious. Both larvae and adults strip leaves until only the veins are left, but the larvae are responsible for the most damage. Feeding damage by larvae first appears as small perforations in the leaf. Plants can die if defoliated for several consecutive years.
Lily beetle attacks lilies and fritillaries. Adults eat away at the leaf margins or make irregular holes in the leaf in spring and early summer, endangering the plant's ability to develop flowers for the following year. Larvae also cause damage by feeding on foliage, starting from the leaf tip. Plants can be defoliated.
Rosemary beetle adults feed on flowers, shoot tips and leaves in spring. Larvae feed on flowers and foliage in autumn and winter. It has been found on rosemary, lavender and thyme.
Asian longhorn beetles will attack healthy trees. Symptoms of feeding damage by larvae include leaf wilting as the vascular system is interrupted, broken or dead branches, dead tops and eventually tree death. Resin bleeding is caused by females making slits in which to lay eggs.
Flea beetle adults and larvae can produce pinprick holes or even skeletonise leaves during feeding, rendering crops unsaleable.
Treatment: biological control
No commercial biological controls are currently available for viburnum, lily, rosemary or Asian longhorn beetles. Research carried out by the RHS and AHDB Horticulture has showed potential for semiochemical control for lily beetles.
Treatment: cultural control
Check fertiliser levels to prevent excessive soft growth - highly attractive to beetles. Yellow sticky traps above vulnerable protected crops can help to attract flea beetles away from foliage. They are an attractant, so use with caution. Control weeds such as willowherbs and bittercress. The Food & Environment Research Agency has strict guidelines on dealing with longhorn beetles. If pests or suspect damage is found on plants or wooden pallets, you should inform your local plant health inspector.
Treatment: chemical control
Target the larval stages with:
Active ingredient Cypermethrin
IRAC code 3
Formulation Toppel 100* (United Phosphorus)
Action(s) Contact synthetic pyrethroid. Good coverage essential. Long residual activity. Incompatible with biological controls.
Active ingredient Deltamethrin
IRAC code 3
Formulation Decis* (Bayer)
Action(s) Contact synthetic pyrethroid. Good coverage essential. Long residual activity. Some products have extensions of authorisation for control of flea beetle on edible rosemary. Incompatible with biological controls.
Active ingredient Lambda-cyhalothrin
Formulation Hallmark WZT* (Syngenta) and others
IRAC code 3
Action(s) Fast-acting, persistent, contact and residual insecticide approved for use on a range of outdoor crops for caterpillar control. Incompatible with biological control.
Active ingredient Nutrient-based plus additional natural products
Formulation SB Plant Invigorator (Fargro)
Action(s) Contact insecticide with physical action. Apply at first sign of damage. Good coverage essential. Take care when using with biological control.
Active ingredient Oxamyl
IRAC code 1A
Formulation Vydate 10G* (DuPont) - end use date 31 December 2016
Action(s) Systemic, carbamate nematicide.
Active ingredient Pyrethrins
IRAC code 3
Formulations Pyrethrum 5EC (Agropharm), Spruzit (Certis)
Action(s) Contact insecticide. Compatible with biological controls if predators re-introduced after seven days.
Active ingredient Thiacloprid
IRAC code 4A
Formulation Calypso* (Bayer), Biscaya* (Bayer), Exemptor (ICL Group)
Action(s) Exemptor can be incorporated into compost. Foliar applications are incompatible with biological control.
Fully updated by Dove Associates
* EAMU required for use in ornamental plant production outdoors and/or under protection. Use plant protection products safely. Always read the label and product information before use. Dove Associates shall in no event be liable for loss or damage to any crops or biological control agents caused by the use of products mentioned.