Contact: Eric Day, Manager, Insect Identification Laboratory
August 1996
Diptera: Agromyzidae, Phytomyza ilicis & P. ilicicola
Plants Attacked
American and English varietites of holly, inkberry.
Description of Damage
Linear or blotch mines are evident on the
upper surface of leaves from July through May. P. ilicis makes a
linear mine; P. ilicicola makes a blotch mine. There are
numerous other species of holly leafminers more or less related
to specific hosts. Japanese and Chinese hollies are not attacked
by leafminers. Adult feeding causes numerous puncture marks on
the undersides of the leaves.
Identification
Adults can be seen in early May when new growth
is 1/2-1" in length. They are jet black, shiny flies about 1/16"
long. Larvae are cream colored to yellowish and one per mine is
usual. Leaves may have one or more mines per leaf. Pupae are
brown to black and located in the leaf attached to a grayish spot
where the adult will emerge.
Life History
Pupation may occur in late fall or early spring.
Adult emergence begins in early May and peaks as new leaves and
shoots begin to develop, about the time old leaves naturally drop
to the ground on American Holly. Adult flies spend a several
days puncturing new leaves with the ovipositor and feeding on
bleeding cell sap. In mid May they insert their ovipositors deep
into leaf tissue from the underside and deposit an egg. Larval
development starts two or three weeks later in June. Larvae
develop slowly until mid or late summer when mines develop into a
large blotch. Larval development is complete by fall. One
generation per year. Overwintering stage - larvae.
Control
Systemic insecticides are highly effective if applied
after eggs have hatched. Dimethoate will injure Chinese Holly
varieties, especially burfordi, but leafminers do not attack
these plants.
Remarks
Be sure to include a precaution against spraying
Chinese Hollies with dimethoate.