How to make the most of garden insects this summer

With the hot weather, insect activity increases – notably pollinators – bringing the garden
alive. The buzzing, swirling activity in gardens is appreciated by gardeners at a time of concern about biodiversity.

Bumblebees are the most conspicuous pollinators. They make nests in the ground or hollow trees, that house up to 400 worker bees plus their queen. Nests die out in late summer but are building up now.

There are 26 species of bumblebee, eight of which are very common in gardens with every other garden being said to hold a bumblebee nest. Solitary bees – where each female constructs her own nest, and dies before her offspring emerge – are even more important as pollinators. Many need bare patches of soil into which to burrow.

Avoid disturbing nests or burrows of these valuable pollinators, leaving undisturbed areas of grass and other vegetation or bare soil.

Caterpillars are the larvae of moths and butterflies that often browse leaves or eat roots. The mullein moth caterpillar is very conspicuous on certain mulleins (verbascum) now – it leaves the plant rather ragged, but the banded caterpillar is disarmingly attractive. Most caterpillars do little significant damage and are best left undisturbed for birds to feed on. Plants soon recover.

The notorious cabbage caterpillars seldom appear in force until late summer when picking off will curb damage. They also suffer from insect diseases and predators such as wasps and parasites.

Predators and parasites, known as beneficial insects, act – often unnoticed – on populations including unwanted insects. In nature, a sort of balance exists between beneficial and less welcome insects. This applies in gardens too where insect harm is moderate most of the time. Gardeners often buy parasitic and predatory insects for release in their greenhouses. Success depends on timeliness.

No predator or parasite can be expected to quickly suppress a heavy infestation, nor thrive in the absence of prey.

Regular monitoring of greenhouses and conservatories will pick up the first signs of whitefly, aphids and red spider mite. Yellow sticky traps can detect whitefly in particular, red spider mite mottles leaves and aphids cause leaves to curl. All these insects particularly relish aubergines. An aubergine is a handy greenhouse sentinel to give early warning.

Red spider mite is particularly likely to be prevalent after the recent hot weather. Prompt ordering of the appropriate control before its prey builds, gives long-lasting suppression, although top-ups may be required at intervals.

Ladybirds and their equally conspicuous larvae devour aphids and scale insects. Aphids start the season with an explosion in numbers, the black bean aphid (blackfly) on broad beans being a notorious example. As expanding colonies become crowded, winged forms arise spreading the aphids widely. A pleasing summer garden ritual is watching aphid populations boom, and then bust, with the arrival of their enemies, including lacewing and sawfly larvae. There may be later outbreaks, blackfly on runner beans for example, but they seldom amount to much on thriving plants.

Rose aphids have come and gone in many gardens but the caterpillar-like larvae of certain sawflies might cause concern. The leaf-rolling sawfly rolls leaves into tubes while the rose slugworm and large sawfly browse the foliage. Severe infestations can be picked off, but often the damage is cosmetic with the plants suffering no long-term harm and continuing to flower.

For more pollinators and beneficial insects, plant plenty of pollinator-friendly flowers. The RHS publishes lists of these – search for “RHS Plants for Pollinators”. Garden centre plants carry a bee logo to indicate pollinator friendliness.

The RHS is a charity inspiring everyone to grow via its research, advisory, outreach, shows and gardens. For more information, visit: rhs.org.uk