Narcissus bulb fly

What is narcissus bulb fly?

Narcissus (daffodils) and some other bulbs can be attacked by the larvae of two different types of fly. The more serious pest is large narcissus bulb fly, as this has larvae that attack and destroy otherwise healthy bulbs. Maggots of small bulb flies are secondary pests that infest bulbs that have already been damaged by another pest or disease.

Symptoms

Signs of an infestation include;

• Affected bulbs are often killed or produce a few grass-like leaves but no flowers. This is not to be confused with daffodil blindness
• The centre of the bulb is eaten out by a plump, creamy white maggot that is up to 18mm long. This is the large narcissus fly which is a primary pest that attacks healthy bulbs
• The centre of the bulb is filled with the larva’s muddy excrement
• If there are several creamy white maggots, up to 6 mm long, in a decaying bulb, these are likely to be larvae of small narcissus flies (Eumerus strigatus and E. funeralis). These are secondary pests that attack bulbs that have been already damaged by other pests, diseases or other injury

Control

Non-chemical control

Adult bulb flies like warm sheltered places, so the level of infestation can be reduced by growing daffodils in more shaded and exposed places.

After flowering, firm down the soil around the plants to make it less easy for female flies to deposit their eggs.

Avoid introducing large narcissus bulb fly and other bulb problems into your garden by buying firm, good quality bulbs from reputable suppliers. Newly acquired high value bulbs can be protected by covering them with insect-proof nets such as Enviromesh, during mid-May to June when the female flies are laying eggs.

Chemical control

None of the pesticides available to amateur gardeners will control large bulb fly larvae.

Biology

Adult large narcissus flies are about 15 mm long and resemble small bumblebees. They have hairy bodies that vary in colour – some are yellowish brown, while others have bands of black, white and/or brown hairs. They emerge on sunny days in mid-May to June, when the females seek out suitable host plants.

Eggs are usually laid on the neck of the bulbs. After hatching, the maggot crawls down to the bottom of the bulb and enters through the basal plate. Once inside, the maggot eats the central portion of the bulb, including next year’s flower buds. The maggot is fully grown by late winter – early spring of the following year.

The larva usually leaves the bulb and pupates in the soil nearby.