- Robert Blake
beneficial insects in the garden
Andrew Halstead, who was the RHS’s Principal Entomologist at Wisley before retirement, is also a beekeeper and gave this informative talk at our 3 February Zoom meeting. He started by emphasising the importance of insects in pollinating plants by picking up pollen from the stamens and transferring it to the stigma of another flower. All types of bees are good at doing this as pollen sticks to their hairy bodies. Bumble bees are much hardier than honey bees, are active from March to October and live in colonies of up to 100 – bird boxes are favourite nest sites. Advice on plants that attract bumble bees can be found at www.bumblebeeconservation.org/gardeningadvice. Red Mason bees are gentle and solitary bees that make their nests in hollow spaces. They like bug hotels, fitted with 7 mm cardboard tubes and placed in a sunny position.
We should welcome the many predators that help to protect our plants against attack by
pests. There are many different types of beetle (e.g. Ground, Devil’s Coach Horse and Stag
beetles) which feed on slugs, caterpillars and aphids. The 2 and 7 spot ladybirds are the
most common ones in the UK and predate aphids. However, the larger 16 spot Harlequin
ladybird, new to Britain in 2004, is a much more efficient aphid predator as it produces three
generations each year. There are also about 300 species of hoverfly which prey on aphids,
leaf hoppers and caterpillars. Ichneumon parasitic wasps are non-threatening, can be found
in gardens as well as woodlands near log stacks, and lay eggs in the bodies of caterpillars of
the cabbage butterfly.
Large infestations of pests can be dealt with using pesticides but their use can kill beneficial
insects. However, insecticidal soap (organic pesticides with fatty acids) can be bought at any
garden centre and will control a wide range of pests such as whitefly, aphids and spider
mites. Yellow sticky traps can be used in greenhouses to indicate the presence of whitefly.
Vine Weevil larvae attack and eat the roots of container plants and can be eliminated by
introducing nematodes in late summer. There are also nematodes for removing slugs but
they work best in sandy soil and are not so effective in heavy clay. Beer traps are probably
worth trying! Snails can best be reduced by attracting song thrushes to your garden as they
eat them by smashing their shells on a stone.