Phytomyza ilicicola Loew, 1872
Ph. ilicicola belongs to a group of closely related species which are highly specialized leaf miners on different Ilex species (Aquifoliaceae) (Kulp, 1968). They are characterized by rather long and thin terminal tubules in the aedeagus which are distally diverging. This character is quite abundant across Phytomyza but not among species of economic importance. The host plants (hollies) are often cultivated as ornamental bushes for parks and gardens. The present agromyzid species is the best known and most important holly miner in the Nearctic region. About the other Nearctic species no serious damage is recorded, they are, thus, not included into this CD-ROM.
IMPORTANT CHARACTERS
Adults
Orbits at most narrowly yellowish on inner margin.
Mesonotum silvery greyish, pubescent, humerus and notopleuron widely dark.
Wing length from 1.6 in male to 2.3 mm in female; second costal section relatively long, 2.5-3 times length of fourth.
Legs basically dark, tibiae lighter than femora, normally brownish. At least the knees of the fore legs are yellowish.
Note: The species is similar to Phytomyza ilicis but smaller and especially the head is darker. Mesonotum heavier pubescent than in ilicis.
Male terminalia
(Phy ilicicola aedeagus.pct, Phy ilicicola aedeagus Sp.pct) with basal vesica relatively short, tapering towards rear; appendages of aedeagus strongly pigmented, large, rectangular.
Immature stages
Anterior spiracles of larva not branching at tip.
BIONOMICS
In spring the females oviposit into young soft leaves. The emergence of the adult flies is well synchronized with the flush of the leaves. During the summer the young larva creates very slowly a narrow linear mine. The main larval feeding activity of the same generation takes place during the winter. This can be explained by an age-related change of the chemical and structural properties of the leaves. "As leaves get older there is a shift in allocation of defense investment away from allelochemicals and towards leaf sclerophylly, spinose teeth and low foliar Nitrogen and water." (Potter and Kimmerer, 1986). The larva feeds usually only on one of the 2-4 layers of palisade mesophyll cells (Kimmerer and Potter, 1987). For pupariation the larvae remain within the mine.
Eggs are laid into the leaf-blade (not into the vein), slow feeding during the summer, feeding continuing through the winter, thus only one generation. Pupation within the mine.
HOST PLANTS
Ilex opaca, occasionally also I. cumulicola and the European holly I. aquifolium.
DISTRIBUTION
USA: Connecticut, District of Columbia, Massachusetts, New Jersey, New York, Ohio.
ECONOMIC IMPORTANCE
Ilex opaca is grown as an ornamental bush in the USA, on which the species can have serious outbreaks. It was observed that infestation in urban sunny areas is higher than in the natural habitat of holly in the undergrowths of forests (Potter, 1992, ...?). Up to 13 mines were found on one leaf (Potter, 1985). The always visible feeding traces of the larvae can have a high influence on the appearance of the plants, because the life span of the perennial leaves can become several years old. Although the leaf miner is mainly an aesthetical problem, especially in nurseries, young plants may be weakened by heavy infestation.