Press Bulletin No. 4.
May I, o901.
Florida Experiment Station.
The White Fly.
This is probably the worst citrus insect in Florida.
It does not kill trees so quickly as some of our scales,
but is very persistent in its attacks upon the leaves, sap-
ping the vitality of the trees, impairing the quality,
flavor and keeping qualities of the fruit, and rendering
both trees and fruit unsightly because of the black sooty
mold, MELIOLA, that invariably develops in the honey-
dew excreted by the insects. The damage to some of our or-
ange growing counties is at present hardly less than a quar-
ter of a million dollars annually and with the rapid ex-
tension of the citrus industry in these sections, single
counties promise to suffer a loss of a half million dollars
each year, within a half dozen years, if present conditions
continue. Extensive and promising experimental work
with fumigation is being conducted by the Station and
.announcements of results will be made as fast as positive
conclusions are reached.
The insects winter on the undersides of the leaves in
their various larval stages, mostly full grown, the first
adult flies sometimes appearing in a particularly favora-
ble spot in South Florida as early as the second week in
February. -The bulk of the brood appear during the first
two weeks in April, continuing until in May. Egg-lay-
ing begins very soon after the adults appear. The eggs
are firmly attached to the undersides of the leaves by
means of a pedicel or stalk. They hatch in from ten days
to three weeks according to the season. The young larvaI
are able to crawl about when first hatched and may be
transported by men or horses working in infested groves;
also by birds and probably by other insects, as lady-bugs.
After hatching. the insects pass through six stages, the
last being the adult or winged form. During these inter-
mediate larval stages the insect does not move about but
remains attached to the same spot upon the leaf, much as
the scale insects do. Both sexes of adults are winged and
live a week or ten days, each female depositing upwards
of two dozen eggs. As many as five or six thousand eggs -
may be laid upon a single leaf. The adults are trans-
ported in carriage tops, railway coaches and by other
similar means. They do not possess powers of prolonged
flight, many of them, perhaps the majority, never leav-
ing the tree upon which they have hatched.
A second brood of adult flies appears in June and Ju-
ly, and a third in September and October, extending into
The most practicable remedy at present is a resin spray
applied during the larval and pupal periods, the first oc-
curing from May 1st until the middle of June, the, second
from the last of July until early September, and the third
from the 1st of November until the last of March.
The following formula for resin spray has given ex-
cellent satisfaction to many of our growers and is recom-
mended because of the convenience of obtaining and keep-
Resin, pulverized, -------- ------------8 lbs.
Caustic Soda (Star Ball Potash,) pulverized, 3 lbs.
Fish Oil ------------------------------- pts.
Boil in a large iron kettle in six or seven gallons of
water until the materials are all dissolved which will usu-
ally be in twenty minutes after the boiling point is reach-
ed. Strain into a barrel holding about fifty gallons and
fill up with water, thus diluting to fifty gallons. It is now
ready for use as a rather coarse spray. As the insects are
on the under sides of the leaves only, care must be taken
to thoroughly wet the under side of every leaf.
When trees are large and tall it is best to have the
pump with two long leads of hose, to lhe end of one of
which is attached a metal pipe about six or eight feet long
with nozzle fastened at the end, and to the other hose a
similar rod twelve or more feet in length. Both hose are
worked from the same side of the wagon, the operator
with the short rod spraying the lower part of an advance
tree, while the operator with the long rod sprays the top
of the tree which operator No. 1 has just left. If the
hose are of sufficient length the operators can shift their
positions enough to thoroughly cover the entire tree, al-
ways thrusting their pipes through the openings between
the branches to the side of the tree opposite to where
they are standing, thus always spraying against the under
sides of leaves. Examination has shown that about sev-
enty-five per cent. of the insects are dead within twenty-
four hours after the application of the spray.
Some growers have had their fruit to fall following
spraying in April and May when the trees werein blos-
som or the fruit was small. Others have sprayed at the
same time without noticeable injury. We regard it safest
to spray the summer and winter broods. Two applica-
tions may be made during the winter if the insects are
very numerous and the trees will have a good clean start
in the spring.
SResin wash is removed by rain and if rain falls be-
fore twenty-four hours have passed after the application,
unsatisfactory results will follow. Three or four spray-
ings will not injure but rather benefit the trees the first
year, but some harm is apt to result if done so frequently
through a series of years. Two thorough and carefully
timed treatments per year is about right, although the
number may have to be increased sometimes, even at the
risk of injury. The fruit will be free from smut and of
far higher quality if the foregoing directions are followed.
Kerosene emulsion, or a ten to fifteen per cent. me-
chanical mixture of kerosene and water applied with a
Gould or Deming kerowater machine will doubtless give
good results, though we have not personally used these
sprays against this insect. The kerowater pumps must
be watched and tested occasionally to see that they are
not throwing more oil than the gauge indicates. The
emulsion is entirely safe.
The insects are killed by freezing and North Florida
has been freed from them during the past several severe
H. A. GOSSARD, Entomologist.