Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 185

Family PSILIDAE

Trypeta zoe (Meigen) ( 427 )
larva

chrysanthemum blotch miner
A minor pest of Chrysanthemum . Attacks of significance
tend to occur most frequently on autumn-flowering or
winter-flowering plants. Certain other cultivated
members of the family Asteraceae are also attacked.
Widely distributed in Europe.

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Small to relatively large, colourful flies; wings with a
pale streak or fold extending from the broken costa.
Larvae typically mine within plant tissue.

Psila nigricornis Meigen
larva

chrysanthemum stool miner
An infrequent but formerly common pest of
Chrysanthemum , occurring mainly where clean stock
plants are not used. Also attacks other herbaceous
plants. Widely distributed in Europe; also found in
Canada.

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DESCRIPTION
Adult: 4-5 mm long; yellow-bodied, with iridescent
wings distinctly marked with brown. Larva: up to 7
mm long; yellowish and rather stout-bodied, pointed
anteriorly and truncated posteriorly.

LIFE HISTORY
Adults occur in the spring, depositing eggs on the leaves
of chrysanthemum and certain other Asteraceae,
including Aster , common ragwort ( Senecio jacobaea ),
groundsel ( S. vulgaris ), mugwort ( Artemisia vulgaris )
and tansy ( Chrysanthemum vulgare ). The larvae then
feed within the leaves during May and June, each
forming a characteristic mine. This feeding gallery
commences as an irregularly rounded blotch but later
develops into an expanded, somewhat linear, mine
which frequently follows the midrib and major veins.
When fully fed, usually in early July, the larvae enter the
soil and pupate. A second generation of adults appears
about two weeks later. Larvae of the second generation
feed during the autumn; they eventually pupate to
produce adults in the following spring.

DESCRIPTION
Adult: 4-5 mm long; shiny bluish black, with head and
legs brownish yellow; antennae mainly black. Larva:
up to 6 mm long; creamy white, tough-skinned and
slender-bodied. Puparium: 4 mm long; dark brown.

LIFE HISTORY
Adults of the first generation occur in May and June,
laying eggs in the soil close to chrysanthemum plants.
The eggs hatch in about two weeks. Larvae then invade
the chrysanthemum stools, and are fully fed in
1-2 months. They return to the soil to pupate. Adult
flies emerge from late August to early October. Larvae
resulting from this second generation feed throughout
the winter, usually taking 3-4 months to reach maturity;
under greenhouse conditions, however, the rate of
development is increased and the first new adults often
appear in February or March. DAMAGE

When numerous, the mines seriously disfigure the
foliage of chrysanthemum plants, affected tissue
eventually turning brown.

DAMAGE
Larvae form long, superficial tunnels in chrysanthemum
roots and stools, the outer tissue drying out and then
splitting open; shoots, especially of cuttings, are also
attacked. Infested plants are weakened and shoot
production is reduced. In addition, attacked cuttings
may be killed. Damage is most significant in stool beds
during the autumn, particularly where early-flowering
cultivars (e.g. cv. Favourite) are used for producing
cuttings in heated greenhouses. Damage may also be
caused to the roots of lettuces planted into infested
chrysanthemum beds.

427

427 Mine of chrysanthemum blotch miner ( Trypeta zoe ).