Syrphid flies; our best allies in the garden

What is a hoverfly?

You’ve probably seen an insect that looks like a wasp, but hover in front of a plant. It is an adult hoverfly. He, or rather she (the female) consumes only pollen, nectar or honeydew, but his larva, which is a voracious predator, consumes aphids.

The adults

Are flies often disguised as wasps or wild bees. But they only have two wings and are also equipped with 2 stabilizers (like all Diptera) which allow them to hover.
If you see a hoverfly hovering in front of a non-flowering plant, chances are aphids are already present on the plant.
An adult female hoverfly may lay several eggs separately near aphid colonies. In 2 to 3 days the eggs hatch and the larvae eat.

the egg

Is small, elongated, barely 1 to 2 mm, white and is usually found on or under a leaf near an aphid colony.

The larvae

This small, legless maggot, often transparent to the point that its internal organs can be seen through its skin, feeds mainly on aphids of all species. He pricks them with his siphon, injects them with saliva to liquefy their organs and sucks up this soup thus obtained as though through a straw. Then it moves on to another aphid.
It only needs about fifty aphids to be able to complete its larval cycle, but as it is insatiable, it will not finish its prey and will very quickly move on to another as soon as the straw flow drops.
A large larva can thus kill between 40 and 100 aphids in one night.

Another particularity is that the larvae are not afraid of ants, unlike ladybug larvae which are often chased away by them. I saw an ant bothering a hoverfly larva. The latter took advantage of the ant being above her to sting her under her abdomen. She lifted the ant which could no longer flee. It was the hoverfly that had the upper hand.
Also unlike ladybugs, they attack all kinds of aphids, possibly also scale insect larvae or other parasitic insects.

The pupa or nymph

Like all insects with complete metamorphosis, the transparent worm will transform into the perfect insect or imago.
But before pupating, it will empty itself of an inky black liquid, like a stain of tar, which will remain the trace of its passage on the plant. It is thus possible to know, in the event of an attack by aphids, whether the hoverflies are present on the site and to look for pupae, eggs or larvae.

the pupa has a characteristic teardrop shape resting on a leaf.
The different species of hoverflies are therefore valuable auxiliaries, early and not very sensitive to cold temperatures, very efficient, with few predators.

The different species.

We are talking about several thousand species distributed in the Palearctic zone, that is to say in our latitudes, but we rarely encounter more than a few species in a garden.

How to get some in the garden?

The easiest way is to have flowers with pollen, because hoverflies are good pollinators, throughout the growing season, from March to November.
They also need prey (mainly aphids). This is why it is absolutely necessary to stop fighting aphids in our gardens, whether with conventional, organic products or “homemade” preparations such as mixtures of black soap, vinegar, various manure and other “junk”. “which do much more damage than they render service.

You can also find them commercially, but if their breeding is not too complicated, they are insects that do not tolerate travel well, which limits their marketing.
Currently we can find Sphaerophoria rueppellii commercially as pupae.

These insects are also considered good markers of biodiversity. In the 1990s they were numerous and declined with the disappearance of prey.

Ask all your questions during the gardening program on Sunday morning on France bleu Isère from 9 a.m. to 10 a.m. by calling 04 76 46 45 45.