There are thousands of species of beetles and weevils (Coleoptera) in our garden world.
They vary greatly in size, appearance and habits. A number of them are garden or household pests, but others are useful predators on other insects and soil creatures. These include the carabid beetles, the devil’s coach horse and tiger beetles. Ladybirds are well-known predators of greenfly.
Beetles have six legs and biting mouth parts. Their forewings are modified to form hard wing-cases and the hindwings, when they are present, are folded beneath them. Most of the weevils can be distinguished from beetles by their long `snouts’. Among the more obvious adaptations for the life they lead are the fierce jaws and long legs for swift running which distinguished the hunters; the hind legs of flea beetles adapted for jumping and those of the water beetles adapted for swimming.
Beetles are found in every part of the garden. In the vegetable plot flea beetles perforate the leaves of brassica seedlings ; the turnip gall weevil (Ceuthorhynchus pleurostigma) damages the roots; pea and bean weevils (Sitona spp.) notch leaves of broad beans and peas; wireworms (click-beetle larvae) attack root crops and asparagus beetles (Crioceris asparagi) feed on the fern.
In the orchard, weevils cause capped blossoms (Anthonomus pomorum), sever the young shoots (Rhynchites spp.) spoil the fruit of raspberries (Byturus tomentosus) and feed on the foliage (Phyllobius spp.). Shothole borers invade unhealthy trees.
Ornamental trees and shrubs also suffer from weevil attack and also from cockchafer larvae feeding at the roots.
Under glass, the vine weevil (Otiorrhynchus sulcatus) is a well-known pest, the larvae feeding on the roots of pot plants and the adult insects making ragged notches in the foliage.
Many beetle pests are to be found in the flower garden. They include the garden chafer (Phyllotherpa horticola) which damages lawns in the larval stage and often spoils rosebuds when adult. The waterlily beetle (Galerucella nymphaeae) makes lily pads ragged and unsightly; weevil grubs feed on primula and other plant roots and chafer grubs may flourish in the herbaceous border, to name but a few.
Most beetles are controlled by spraying their host plants with insecticide and repeating the application 14 days later. The larvae may be treated by applying 5 percent insecticidal dust to the soil at the rate of about 28g (1 oz) per sq m (sq yd) and potting compost may have it incorporated at the rate of 0.250.30kg (8-10oz) per bushel.
Bark Beetles There are several species of these small beetles which attack trees and shrubs, including fruit trees, especially those in poor health through disease, unsuitable conditions at the root or damage such as broken branches, etc.
The female beetles burrow between the bark and the wood and lay eggs in the tunnels. When the legless, white grubs hatch, they extend the galleries, thus making complicated patterns which earn them the name of ‘engraver beetles’ .
In due course, the larvae pupate and emerge through conspicuous exit holes. Among the most destructive species are the fruit bark beetle (Scolytus rugulosus) and the large elm bark beetle (Scolytus scolytus).
It is advisable to burn all dead branches and to remove the bark from any larger limbs or felled tree trunks which may harbour the beetles.