Merodon equestris F Large narcissus fly

The large narcissus fly is mainly a pest of daffodil and narcissus; various other ornamental bulbs, but not tulip, are also attacked. The inner tissue of larva-infested bulbs is destroyed and the resulting cavity becomes filled with rotting tissue and blackish frass. Infested bulbs feel soft, especially in the neck region. If planted, damaged bulbs give rise to weak, discoloured and distorted foliage and poor-quality flowers; sometimes, growth is limited merely to the emergence of a ring of narrow, grass-like leaves. Although widely distributed, in the British Isles this pest is of most significance in southwestern England.

BIOLOGY

Unlike species of Eumerus (p. 177 et seq.), the large narcissus fly is univoltine, and adults are active in calm, sunny weather at any time from late April to July. Eggs are laid singly on the neck of a bulb or in the soil, especially where the egg-laying female can gain access through a soil crevice; the eggs may also be laid low down upon withering foliage of host plants. Eggs hatch in approximately 2 weeks, and each neonate larva immediately crawls down the bulb and bites its way in through the base plate. Further development occurs within the bulb. Larvae are usually fully grown by the winter. They pupate in the spring, usually in the neck of the infested bulbs. In forcing houses, development of the pest may be accelerated and adults often emerge as early as February.

DESCRIPTION

Adult 2-14 mm long; body bumblebee-like, clothed mainly in gingery-brown hairs but hairs often forming black, grey or reddish crossbands (Plate 6f). Egg 1.6mm long, elongate-oval, pearly-white. Larva up to 18 mm long, stout-bodied, dirty yellowish-white; posterior respiratory cone dark brown.

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