Chromatomyia syngenesiae Hardy, 1849
IMPORTANT CHARACTERS
Adults
Wing length: 2.2 - 2.6 mm. Arista is more gradually tapering than those of Chromatomyia horticola (von Tschirnhaus, 1969). The apical section is longer than the basal one. Palps with several small lateral holes (hardly visible in dry specimens) (von Tschirnhaus, 1969 and personal communication). The head is rather light at the dorsal side.
As in horticola, acrostichals are missing. Tergites with posterior elongated hairs only laterally. In the case of any doubt, the genitalia should be studied.
Immature stages
Very similar to Chromatomyia horticola.
BIONOMICS
Oviposition can take place on either surface of the leaf but the upper surface is preferred (Spencer, 1973). Foliage in the lower shaded portion of the plant or on completely shaded plants seems to be preferred by for oviposition (Gurney, 1960). The larvae form irregular linear mines.
The larva hatches in about 4-6 days, depending on the temperature. A long, irregularly linear mine is formed, with frass normally deposited in distinct, well-separated grains but there appears to be some variation in the form of frass deposits, possibly depending on the nature of the host-plant. Pupation takes place in the mine.
The complete development of larva and pupa ranges depending on the temperature of 16 to 33 days (16-25°C, constant temperatures) (Cheah, 1987). At 20°C the larval development lasts 7-12 days and the puparial period 9-13 days (Ibrahim and Madge, 1978). A similar generation time (28 days) was also observed by Frick, 1972.
HOST PLANTS
The main host group is most probable the Asteraceae but in USA it was also found on Pisum. European specimens from Sonchus and Lactuca were experimentally transferred to Pisum (K.A. Spencer and N.W. Hussey in: Spencer, 1973).
Crops known to be infested by Chromatomyia syngenesiae (Spencer, 1973):
Asteraceae: Cynara scolymus L. (artichoke), Lactuca sativa (lettuce), Cichorium endivia L. (endive) and many ornamentals, of these especially Chrysanthemum and Gerbera.
Fabaceae: Pisum sativum L.
Apiaceae: Daucus carota L.
DISTRIBUTION
Europe; less common in the south but isolated records from Italy, Spain and Canary Islands; North America: Canada, USA: mainly California, Oregon, Washington, also known from Massachusetts and Rhode Islands; Australia, New Zealand.
West Europe can be interpreted as the main center of distribution. The localized records in other regions indicate human introduction (Spencer, 1973).
ECONOMIC IMPORTANCE
The most serious damage is caused on lettuce and on Chrysanthemum (Spencer, 1973). In Europe the species is of considerable significance especially in glasshouse cultures.
Lange et al., 1980 mentioned that Chromatomyia syngenesiae as other agromyzids regularly build up higher populations after insecticidal treatment against other insects. This is caused by the death of the naturally occurring parasitoids controlling agromyzids. Parasitoids are often more vulnerable to pesticides than their hosts.