Liriomyza bryoniae (Kaltenbach, 1851)
Closely related to Liriomyza strigata and Liriomyza huidobrensis. No undisputed morphological characters are available for the separation of huidobrensis and strigata. However, the combination of the mines, which are not associated with the veins and the midrib of the leaf, and the peculiar aedeagus are good diagnostic characters. Furthermore the generally lighter coloration of the cuticle in the vicinity of the vertical bristles should be taken into account.
IMPORTANT CHARACTERS
Adults
Wing length: 1.75 - 2.1 mm. Frontorbits distinctly projecting above eye in lateral view (Spencer, 1973), not visible in alcohol material. Hind margin of eye black, cuticle around both vertical bristles yellow.
Anepisternum yellow with a straight black bar on the lower margin.
Male genitalia
Hypandrium large and thin; basal part of aedeagal apodeme almost straight; ejaculatory apodeme of intermediate size; surstyli rather broad and short (figs?) with 1 apical spine and thinner hairs. Gonites as in 'normal' Liriomyza; terminal part of distiphallus consisting of two sclerotized parts, terminal tubules well visible (Figs).
Immature stages
The numerous bulbs of the posterior spiracles are arranged semicircular. Below the posterior spiracles subspiracular processes can be found. The larvae form irregular linear leaf mines.
BIONOMICS
The following information comes mainly from Spencer, 1973, who used the following sources: Speyer, 1937; Speyer, 1939; Speyer and Parr, 1945; Speyer and Parr, 1947; Speyer and Parr, 1949; Speyer and Parr, 1950; Speyer and Parr, 1952. Further references are given in the text.
Feeding punctures occur both on cotyledons or young leaves. Eggs are mainly inserted in the upper surface of the leaves but oviposition in the lower side may occur. The larvae live as leaf miners. If a cotyledon or young leaf is not large enough to provide sufficient nourishment, larvae can move up through the stem via a petiole into a second or a third leaf.
As most other agromyzid larvae the fully grown larva cuts a characteristic semicircular exit slit in the epidermis of the upper leaf surface, remains within the mine for a further hour or so and then normally drops to the ground, penetrates the soil just below the surface before actually pupating. However, several authors observed that a part of the puparia of variable size (Saito, 1988: 50%) remains attached to the upper or lower surface of the leaves. That may be partly due to control measures: In applying control measures against soil dwelling puparia, those remaining at the host plants are selected and survive.
Recently some more laboratory experiments on the developmental time correlated to different temperatures were carried out among others by Nedstam, 1985, Saito, 1988, Minkenberg and Helderman, 1990. The results differ not remarkably and may be summarized as follows:
Complete development:
15°C 41 days
20°C 21-27 days
25°C 17 days
30°C 14-15 days
Threshold for development: 8-11°C.
Maximum number of eggs 107-170.
HOST PLANTS
The species is highly polyphagous, Spencer, 1990 listed 16 families which contain host species. The native host in Europe appears to be Bryonia (Cucurbitaceae) (Spencer, 1990). The main crops attacked are Lycopersicon esculentum L. (tomato), Citrullus vulgaris Schrad. (watermelon), Cucumis melo L. (melon), Cucumis sativus L. (cucumber) and Lactuca sp. (lettuce).
DISTRIBUTION
Essentially palaearctic, records from Western Europe, North Africa, Canary Islands, the former USSR, Iraq, India, China, Korea, Japan and Taiwan.
In northern Europe bryoniae is normally restricted to glasshouses and botanical gardens and rarely occurs outdoors (Spencer, 1973, Minkenberg and van Lenteren, 1986).
ECONOMIC IMPORTANCE
One of the major agromyzid pests in the palaearctic region. The species is of particular importance in greenhouses. Among the high number of potential host plants tomatoes and cucurbits seem to be the preferred ones (Spencer, 1973).
Strong infestation of this leaf miner can cause considerable yield reduction and even the death of the whole plant. However, nowadays bryoniae populations in greenhouses can be successfully controlled by commercially available parasitoids (see literature).