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Leaf Miner

Hi Alisdair, Our University of California Master Gardeners just had a short
lecture on leaf miners and may have some help for your local Leaf Miner
problem. There are many specific Leaf Miners so best to get it identified.
Here is the information regarding the holly leaf, which comes closest to
the Citrus you were speaking of:
			DIPTERA
	Compositae, and are often quite injurious. Pupation occurs within the
mines.  The species occurs in various parts of the United States and in
California, Oregon, and British Columbia in the west.  The maggots are
killed in the mines by spraying with 1 part of 40 percent nicotine sulfate
to 400 to 600 parts of water
	The holly leaf miner, Phytomyza iliciola, mines the leaves of American and
English holly and occurs in Alaska, Washinton, Idaho, Oregon and
California. P. obscurella Fallen, mines the leaves of lupine in CAlifornia
and also occurs in Oregon, Washington, and Idaho
AGROMYZIDAE	 Leaf Miners.
	The serpentine leaf mminer, Agromyza scutellata Fallen (A.pusilla Meigen),
is 2mm. long, black, with much of the head, parts of the thorax, legs, and
abdomen, the halteres and scutellum yellow.  The minute white eggs arelaid
just under the epidermis of the leaf tissues and hatch in 4-6 days.  The
maggots are yellow with black mouth hooks and when full grown are 3-4 mm.
long.  They make long winding mines under the epidermis of the leaves
ofalfalfa, beans, garden and sugar beets, cabbage, burr clover, red clover,
white clover, sweet clover, cotton, cowpeas, smooth rock cress, fenugreek,
malva, milkweed, horse mint, hedge mustard, nasturtiem, sweet pea, pepper,
plantain, potato, radish, rape, spinach, tobacco, turnip, vetch and
watermelon.  Pupation occurs in the mines or in the ground in the oval
shining brown puparia.  The life cycle during the summer requires about 23
days.  There are from three to five generations a year.  This miner is most
abundant and injurious in the Southwestern States of New Mexico, Arizona,
and Southern California.  It is common throughout California, Oregon,
Washington, Idaho, Wyoming, Utah, Colorado, and the United States in
general.  Because of thenumerous parasites, the leaf miner is not a
generally serious pest, but is sporadic in its attacks.  The cutting of
forage crops and deep plowing of the land after the harvest of cultivated
crops aid greatly in reducing the numbers.  

Well after reviewing all the above ....not sure it applies at all to your
particular problem but it was interesting anyway. The speaker, our resident
entomologist, added that most commercial growers, of cotton anyway, don't
bother treating for the pest as it does not affect the end product. It
would look awful on Citrus leaves though, (I've got thrips curling my
Citrus right now) and could be detrimental to spinach I would conclude. 
Enjoy your posts.
Lorraine Hoag, University of California Master Gardener, Coordinator,
sutter/Yuba Counties.
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