Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 183

Eumerus strigatus (Fallén)
A small narcissus fly
This fly is essentially similar to Eumerus tuberculatus
but has a wider host range, including Colchicum ,
hyacinth ( Hyacinthus orientalis ), Iris , Lilium and
Narcissus ; the larvae also invade vegetable crops such as
carrot, onion, parsnip and potato, increasing damage to
previously injured tissue. Adults are distinguished from
those of E. tuberculatus by the yellow or light brown
pterostigma on the fore wings and by the absence of a
basal projection on the hind femora.

British Isles most numerous in south-western England.
Also present in parts of Australasia, Japan and North
America.

DESCRIPTION
Adult: 12-14 mm long; stout-bodied and very hairy, the
body hairs ranging in colour from black to greyish,
yellowish, orange or red and often forming a bumblebee-
like pattern; each hind leg bears a characteristic tooth-
like projection. Egg: 1.6 mm long; elongate-oval and
pearly white. Larva: up to 18 mm long; dirty yellowish-
white and plump, with a short, dark brown respiratory
cone at the hind end, bordered on either side by small
inconspicuous tubercles. Puparium: 10-12 mm long;
brownish.

Merodon equestris (Fabricius) ( 423-424 )
Large narcissus fly
A locally important pest of Narcissus ; various other
cultivated bulbs, including belladonna lily ( Amaryllis
belladonna ), Galtonia , hyacinth ( Hyacinthus
orientalis ), Iris , snowflake ( Leucojum ), snowdrop
( Galanthus nivalis ), squill ( Scilla ) and Vallota are also
attacked. Widely distributed in mainland Europe; in the

LIFE HISTORY
Adults occur mainly from May to July but individuals
may appear as early as February in forcing houses. In
cool, inclement weather, they hide in hedgerows and in
other suitable situations, but in favourable conditions
they visit various flowers in search of nectar. They may
also be found sunning themselves on nearby banks,
posts, tree trunks and leaves. In flight they emit a
characteristic, bee-like buzz, and often occur in large
numbers in narcissus fields during warm, sunny
afternoons. Eggs are deposited singly, either on foliage
in the neck region of host bulbs, or directly on the bulb,
or in the soil, the female usually crawling into the hole
left by the withering foliage and flower stem. Most eggs
are laid in June and early July. Eggs hatch in about two
weeks. Each larva then crawls to the base plate of a bulb
before burrowing in to begin feeding. The tissue
immediately around the larval entry hole soon turns
rusty red. This becomes visible if the dead tissue around
the base plate is scraped away. At first, the larva
(typically one per infested bulb) quickly hollows out a
large cavity which becomes filled with blackish frass
and rotting tissue. Larvae normally complete their
development in the original bulb but will move from
bulb to bulb if necessary; most individuals become fully
grown by the winter. Pupation occurs in the following
spring, either in the neck region of the bulb or in the
soil. Adults emerge 5-6 weeks later.

423

423 Large narcissus fly ( Merodon equestris ).

424

DAMAGE
Infested bulbs become soft, particularly in the neck
region, and much of the inner tissue is destroyed. Small
bulbs are often completely destroyed and, if planted, fail
to grow. Larger ones may appear sound, but will
produce weak, distorted, yellowish foliage or merely a
ring of small, grass-like leaves. 424 Larva of large narcissus fly ( Merodon equestris ).