PRESS BULLETIN No. 97.
Florida Agricullural Experiment Stallon.
WHITEFLY CONTROL BY FUNGI.
BY E. W. BERGER.
There is still time during September in which to introduce fungus. The
earlier this is done, the better. For introducing fungus use the method of
spraying the spores (germs) of the fungus mixed in water against the under
surfaces of the whitefly-infested leaves. Several trees treated with the red
Aschersonia by this method at DeLand on April 21 and 22, 1908, had nearly
half of the whitefly larvae on them infected and dead by the middle of the
following June. Other trees treated in the same way and with the same fun-
gus at New Smyrna on Nov. 29, 1907, showed similar results by the twenty-
first of August of this year. Other experiments have not been equally suc-
cessful. In some instances the causes of failure are not well understood; in
others it was doubtless due to the extreme drouth. There are, however, only
one or two instances in which the writer failed to get any growth of fungus at
all, when good fresh material was used between the dates of April 21 and
WHEN TO APPLY THE FUNGI.
It is at those times when the larvae are young (first, second, and third
stages) and abundant, that the fungus can be most readily started. For
some time past young larvae of the first, second, and third stages have been
abundant in whitefly-infested trees, and they will continue to be more or less
abundant until about the end of November. It should, therefore, be an easy
matter to start a growth of fungus now. Fungus can be introduced at any
time from about April till November; except perhaps during a brief period in
May or June, just before the issuing of the second brood of adult whiteflies,
At that period so many of the larvae would be in the fourth and fifth stages,
when they appear to be immune to infection by fungus, that little success
might be attained. December, January, February and March are not favora-
ble for the introduction of fungus, probably because the larvae of the whitefly
are then almost all in the fourth or fifth stages.
PRECAUTIONS TO BE TAKEN.
Use fungus which is well matured. This should be either of a bright red
or a bright lemon-yellow color, according as it is the red or the yellow spe-
cies which is taken. Since much of the summer's growth of fungus fre-
quently becomes weathered or drops from the trees before the following
spring, it is believed to be best to use plenty of it now, and if it is still avail-
able, to introduce more next spring. Rains immediately following introduc-
September 19, 1908.
tions of fungus appear to be conducive towards getting a good growth; but it
is not necessary to wait for rain when spraying.
Cut down the chinaberry, umbrella tree, and .other food plants of the
whitefly (see Bulletin 88), and so stop the infestation spread by these.
TWO SPECIES OF WHITEFLY WHICH REQUIRE DIFFERENT FUNGI.
The fact that the citrus whitefly of Florida represents two distinct and
easily distinguished species has only recently been established by the writer.
This discovery is of importance, since it appears that the yellow Aschersonia
will not thrive upon the species A, which has smooth and generally light-
colored eggs, pupa cases which do not collapse when empty, and adults with
unmarked white wings. The yellow Aschersonia appears to thrive only upon
the other species B, which has rough eggs, covered with a microscopic net-
work of six-sided meshes, and generally dark or black. The pupa cases col-
lapse when empty, and the edges of the slit through which the adult emerged
become more or less folded inward into the empty case. The adults have
white' wings with a smoky-colored area visible towards the end of each fore-
wing, when these are viewed as they lie folded on the back of the insect.
These distinctive characters can be made out by the use of a hand magnifier.
The red Aschersonia and the brown fungus are known to thrive on species A,
but will also grow, to some extent at least, on species B.
If there is any doubt in regard to which species is present, send specimens
to the Experiment Station for identification. It is important to know which
species is being dealt with, in order to know which fungusto use.
For more detailed information write to the Experiment Station at Gaines-
ville for bulletin 88, and for press bulletins 80, 82 and 88.
State papers please copy.