• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 History and distribution
 Appearance of woolly whitefly
 Control of woolly whitefly
 Severity of infestation
 Life history of woolly whitefl...
 Damage caused by woolly whitef...
 Habits
 Food plants
 Fungus enemies
 Insect enemies
 Spread of woolly whitefly...
 Reference














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 126
Title: Woolly whitefly
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Permanent Link: http://ufdc.ufl.edu/UF00027692/00001
 Material Information
Title: Woolly whitefly
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 126
Physical Description: Book
Language: English
Creator: Watson, J. R.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1915
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Bibliographic ID: UF00027692
Volume ID: VID00001
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Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 79
    Table of Contents
        Page 80
    History and distribution
        Page 81
        Page 82
        Page 83
    Appearance of woolly whitefly
        Page 84
    Control of woolly whitefly
        Page 85
    Severity of infestation
        Page 86
        Page 87
    Life history of woolly whitefly
        Page 88
        Page 89
        Page 90
        Page 91
    Damage caused by woolly whitefly
        Page 92
        Page 93
    Habits
        Page 94
    Food plants
        Page 94
    Fungus enemies
        Page 95
        Page 96
    Insect enemies
        Page 97
        Page 98
        Page 99
    Spread of woolly whitefly in Florida
        Page 100
        Page 101
    Reference
        Page 102
Full Text


March, 1915


UNIVERSITY OF FLORIDA

Agricultural Experiment Station




THE WOOLLY WHITEFLY

BY

J. R. WATSON


Fig. 29.-First and second-stage larvae, and eggs. Magnified.

The Station Bulletins will be sent free upon application to the Experiment
Station, Gainesville, Florida.

THE E. O. PAINTER PRINTING CO., DE LAND, FLA.


Bulletin 126

















CONTENTS
PAGE
History and Distribution .---------------------------------------- 81
Appearance of Woolly Whitefly -------------------------------------- 84
Control of Woolly Whitefly -------------------------------------- 85
Severity of Infestation -------------------------------------- -- 86
Life History of Woolly Whitefly ------------------------------------- 88
Number of Broods ..--------------------------------------- 91
Damage caused by Woolly Whitefly -------------------------------------- 92
Habits ------------------------ ------------------------- 94
Food Plants ------------------ -------------------------- 94
Fungus Enemies .----------------- ------------------------ 95
Insect Enemies ------------------------------------------- --- 97
Percentage of Parasitization ------------------------------------ 99
Spread of Woolly Whitefly in Florida ---------------------------------- 0oo
References --------------------------- ----------------- I02




SUMMARY

1. The woolly whitely is rapidly spreading, and will soon be found over
all of citrus Florida.
2. It usually does little damage; but it is capable of causing the almost
total loss of the year's crop, and a severe check to growth.
3. Unless preventive measures are taken, a severe attack will be followed
by a marked rise in the amount of purple scale, which will inflict equal or
greater damage.
4. The miscible oils are effective against the early stages of the larvae
of the woolly whitefly.
5. Both the red and brown fungi have been found growing sparingly on
the woolly whitefly. A species of Cladosporium probably sometimes kills up to 80
per cent.
6. The woolly whitefly is heavily parasitized by a minute wasp-like enemy,
which sooner or later controls an outbreak. Because of this, it probably will
never develop into as permanently serious a pest as is the common citrus white-
fly. The parasite, apparently, does not control the late winter brood.










THE WOOLLY WHITEFLY
(Aleurothrixus howardi Quaintance)
BY
J. R. WATSON


HISTORY AND DISTRIBUTION
This species of whitefly first attracted the attention of ento-
mologists in Cuba, where it was collected in 1903 and 1905. It was
described and named by A. L. Quaintance (I) in 1907, as Aleurodes
howardi. He revised the family in 1914, and placed this species in
the newly created genus Aleurothrixus (15). In Florida the woolly
whitefly was first observed at Tampa in November, 19o9, by E. A.
Back (4). As it was distributed over a considerable part of the city
at that time, it had probably been in Tampa at least several months.
That it had existed there for a much longer period is thought im-
probable by Dr. Back, as it would have been noticed before, since
the trees in question had been under fairly close observation. Judg-
ing from its rapid spread in Florida, a few months would give it
ample time to spread over as much territory. It was in all probability
introduced into Florida from Cuba, since its greatest abundance
was along the water front when first discovered in Tampa, and
there is an extensive commerce between Tampa and Havana. We
know nothing as to the method of its introduction. It may have
been introduced with nursery stock, but it is not necessary to assume
this. Its sluggish habits and the history of its spread in Florida,
would render probable the view that the adult whiteflies have been
brought over clinging to some ship, or to the clothes of some trav-
eler.
When the writer first made its acquaintance, in the fall of 191 I,
it was found in all sections of Tampa and Ybor City, at Lake Mag-
dalene 7 miles west, and at Limona to the east. It had also made
its appearance in Lakeland (9). In the past two years it has spread
rapidly, until now (December, 1914) it is fairly generally distrib-
uted over Hillsborough, Pinellas, Manatee, Polk, and DeSoto coun-
ties. It is generally distributed about Fort Myers, on Sanibel Island,
and as far up the Caloosahatchee River as Alva. It occurs at Ritta






Florida Agricultural Experiment Station


Fig. 30.-Leaf infested with woolly whitefly.


Fig. 31.-Portion of leaf showing early larval stages and
egg-circles. Magnified.






Bulletin 126


in Palm Beach County, on the south shore of Lake Okeechobee,
and at Orlando in Orange County. Dr. Back (8) reports it as
having been found in Miami as early as 1912. We have, however,
received no further reports from that region; nor have we found
any specimens, although the groves in that vicinity have been fre-
quently visited by the writer and other station workers. It would


Fig. 32.-Pupa-case of woolly whitefly (magnified).


seem that the Miami colony failed to become permanently estab-
ished. At the present rate of spread it will be a matter of but a
few years until this species is found all over citrus Florida.
Outside of Florida and Cuba, it occurs in Porto Rico, the Isle
of Pines, and "generally in the West Indies" (Back, 8).






Florida Agricultural Experiment Station


APPEARANCE OF WOOLLY WHITEFLY
From the common citrus whitefly (Dialeurodes citri, formerly
Aleurodes citri) and the cloudy-winged whitefly (D. citrifolii,
formerly A. nubifera) this one is, in the pupa stage, readily distin-
guished by the copious covering of long curly waxen filaments
which have given it the name of woolly
whitefly (Figs. 30, 31 and 32). In the lar-
S val stage it is distinguished by the waxy
fringe encircling the insect (Figs. 29 and
33). The pupa-case, when divested of the
woolly coat is brown, but covered with a
mealy secretion of wax. There are thus
in this whitefly three separate kinds of waxy
secretion: (i) the woolly coat of 'long
curled filaments. that project up from the
pupa case; (2) the fringe, which forms a
Fig. 33.-Second-stage larva waxy band around the larva. and comprises
of woolly whitefly. some filaments on the dorsal side of the
larva and pupa; and (3) the mealy-like
flakes of wax that cover the pupa-case and, less abundantly, the
body of the adult. The pupa-case itself is prominently angled as
compared with that of the com-
mon whitefly. (See Fig. 34.)
The only citrus insect
with which the woolly whitefly
could be readily confused is the
bay or waxy whitefly (Para-
leurodes perseae Quaint.) The
latter is furnished with waxy
rods which break up, when the
adult emerges, into short rods
that lie scattered about the slug-
gish winged insect. Instead of
being curled and woolly, these
rods are nearly straight. They
lie close to the leaf and parallel
to its surface, instead of rising
more or less perpendicularly
and forming a mat of some ap-
preciable thickness as occurs in
Fig. 34.-Pupa, with the wool and the woolly whitefly. Honey-
wax removed. dew does not collect in drops
dew does not collect in drops






Bulletin 126


on the bay whitefly, as it does in the case of the woolly whitefly
(Fig. 33). The bay whitefly is a common sight in citrus groves,
especially in the southern part of Florida. It is less common at
Gainesville and north of that city. It is seldom abundant in a grove.

CONTROL OF WOOLLY WHITEFLY.
Our spraying experiments show that the woolly whitefly will
yield to the same sprays which have been found to be most effica-
cious against the other citrus whiteflies, namely the miscible oils;
but the spray should be applied while the insect is in the early stages.
The pupa is so well protected by the growth of waxy filaments
matted up with honeydew and various molds, that it is difficult to
reach it with a spray solution.
From Fig. 37 it will be seen that the periods in the life his-
tory favorable for spraying will occur about the first of March,
during the first half of June, about the middle of August, and about
the first of November. In cases where the cloudy-winged whitefly
is also present in the grove, it would be well to wait until about the
middle of November, and thus kill both species at one spraying. In
groves where the common whitefly is also present, one should, by
spraying very early in April, do satisfactory execution among the
larvae of both species; although the date would be rather late for
the woolly whitefly, and probably a little early for the other. The
spraying in late August would also kill the cloudy-winged whitefly
as well as the woolly whitefly.
It will probably seldom or never be necessary to spray as often
as four times a year for the woolly whitefly. In most cases where
it seems desirable to use insecticides, it will be found that a single
spraying or at most two a year, will, in connection with the work
of its parasite, control this insect.
Among the miscible oils which are recommended, one of the
best is the formula worked out by W. W. Others of the U. S. Bu-
reau of Entomology, who is located at Orlando (io). To make
this, place in a five-gallon receptacle eight pounds or one gallon of
whale-oil soap. Then add two gallons of a paraffin oil of a specific
gravity of 24 to 28 degrees Baume. Junior Red Engine Oil, (which
can be obtained from the Standard Oil Company, and most insecti-
cide houses), or the Red Insecticide Oil sold by the Gulf Refining
Company, are the best. Pour the oil into the soap gradually, stirring
vigorously all the while, pouring a little oil at a time, and stirring
until no free oil is to be seen on the top of the soap. Continue






Florida Agricultural Experiment Station


stirring until all the oil has been poured in. Add one gallon of
water to the emulsion, about one quart at a time, stirring constantly
as before. The emulsion is complete when, on adding a little of
it to soft water, there is no free oil floating on the surface of the
water. If oil does float on the surface you have not stirred enough,
or you have added the oil too rapidly. If further stirring does not
remedy the trouble, add more soap until the oil is all emulsified.
When ready to spray, dilute the emulsion to make 200 gallons of
spray solution.
If one wishes more minute directions, he should write to the
U. S. Department of Agriculture, Washington, D. C., for circular
168 of the U. S. Bureau of Entomology;,r. to the Florida Station
for bulletin 123. (Through a mistake, the distillate oil formula
was printed in bulletin 123, instead of the above formula. The dis-
tillate is good, but not equal to Yothers' formula as given above.
The directions given in bulletin 123 are for Yothers' formula. This
solution can be bought already mixed from some of the insecticide
houses.)
There are several proprietary brands of insecticides widely sold
and used in Florida which are similar to the above in composition.
These are ready for use, except for mixing with water. The grower
should, however, avoid those containing carbolic acid, sulphuric
acid, or other chemicals that are apt to damage fruit or leaves.
Whale-oil soap will be found to be quite satisfactory against
the whitefly. Use one pound, with six gallons of soft water or four
gallons of hard water.
Experience has shown that this insect is eventually brought
under control by its enemies, and especially by the wasp-like parasite
Eretmocerus haldemani. But, in the case of even a moderate infes-
tation, it is not wise to depend solely on the parasites to control the
woolly whitefly, on account of the increase of the purple scale.
Spray with one of the miscible oils. These oils will doubtless kill
some of the parasites, but there are comparatfiely fewer about at
that time than when the adult whiteflies are emerging.

SEVERITY OF INFESTATION.
The amount of harm that this insect has done to the groves
it has infested has been very variable. In the great majority of
cases the owner has scarcely been aware of its presence. A few
dozen leaves per large tree showed colonies for. a few weeks, after
which the woolly whitefly died out so that it was difficult or im-






Bulletin 126


possible to find live material, although the old colonies, dried out
and matted down, were visible on the trees for several months or
even a year. These old colonies are rendered more conspicuous by
becoming heavily infested with purple scale, causing the leaves to
turn yellow at those spots (Fig. 35).
















Fig. 35--Purple scale following woolly whitefly (from Bul. 123.)

In other instances the infestation has been more persistent, the
woolly whiteflies becoming more or less permanent residents of the
trees; where they may do nearly as much damage as the common
whitefly. This has been the case with certain dooryard trees in
West Tampa for the past three years.
In two groves in Lakeland, about a mile apart, the woolly
whitefly, during the spring and early summer of 1913, inflicted
much more damage than the common whitefly (Dialeurodes citri)
ever did in the same length of time. These cases are so instructive
as illustrating the amount of damage that this species is capable of
inflicting, that they -deserve a somewhat detailed account.

On May 14, 1913, the writer was called to Lakeland to advise a grower
in regard to the woolly whitefly. The trees in a part of the grove were found
to be heavily infested. The under side of most of the leaves was white, and
honeydew so abundant as to cause not only the leaves but the smaller limbs as
well to droop markedly. As one observer remarked, the trees "looked as if
they had been turned upside down and snowed on." If one touched a branch
he brought down a 'sihwer of the honeydew (which is much more sticky than
that excreted by the pther species). Mules which had been used to cultivate the
grove became so covered that the owner, finding that he was unable to wash
it off, became alarmed about them. The insects were mostly in the pupal stage,
with numbers of adults emerging, and some were in the later larval stages.







Florida Agricultural Experiment Station


Some attempts were made at spraying, but these were not very successful, as the
mats of wool and honeydew prevented the sprays misciblee oils and whale-oil
soap) from penetrating to the pupae. Numbers of the adults (estimated at 50
per cent) were hit and killed, owing to their sluggish habits, which resulted
in their failing to take to the wing promptly and escape as the other species of
whiteflies would have done. Because of the comparative inefficiency of the
spraying it was thought best to postpone any further attempts until a more
favorable period in the life-history of the insect. The owner stated that he
had been noticing the woolly whitefly in his grove for about a year, during which
time it had been getting constantly more abundant. At this time the other
grove (Grove B) had quite a heavy infestation but not nearly as heavy as in
Grove A. Grove B was not sprayed.
The groves were visited again on June ii. The woolly whitefly was found,
on the average, in the second-larval stage, and consequently in a much more
favorable stage for spraying. Grove A was thoroughly sprayed with one of
the miscible oils. This sprayed grove had about the same degree of infestation
as on the previous visit, while in the unsprayed grove (Grove B) the infestation
was very much worse than in May, and fully as bad as in the sprayed grove,
in spite of its later start. This would seem to indicate that our first spraying,
although applied at the wrong period in the life-history of the insect, had held
the whitefly at a standstill. At this time the wasp-like parasite was becoming
noticeably abundant in both groves.
On July ii the groves were again visited. There was a marked diminution
in the numbers in the sprayed grove (A), while there was little or none in the
other. The parasite was more abundant. In August the groves were visited
by the writer's assistant, A. C. Mason, who reported that there was little live
whitefly to be found in either grove. The parasite had obtained the upper hand.
The groves were again visited in late October. There was very little living
woolly whitefly to be found in either grove. The trees in the sprayed grove,
although still showing the old colonies, were apparently little the worse for
their experience, except that there was much purple scale present and very little
fruit on the affected trees. (A large part of the grove never became infested.)
The unsprayed grove (B), on the other hand, was in bad shape. The purple
scale was exceedingly abundant. Nearly fifty per cent of the leaves had either
fallen or were yellow and about to fall, and there was very little fruit.
The groves were again visited in February, 1914. Diligent search through-
out the sprayed grove yielded only one leaf with living woolly whitefly (show-
ing only a half dozen larvae). The infested trees had made good growth and
were putting out abundant bloom. The unsprayed grove was receiving good
care and a great deal of dead wood had been cut out. There was still much
purple scale present in it, but no live woolly whitefly was seen. The cause of
this heavy infestation of purple scale following the woolly whitefly is explained
below.

LIFE HISTORY OF WOOLLY WHITEFLY.

The individual eggs are light colored when first laid, but soon
turn to a very dark brown. They are about one hundred and twen-
tieth of an inch in length, and half as wide. They are curved,
shaped like a very short sausage and larger at the anterior end
(Fig. 36). They lie in a circle on their convex surfaces, with the
larger anterior end pointed away from the center of the circle.
(See Fig. 29.) They are attached by a stalk which is about half






Bulletin 126


the length of the egg, and is inserted about one-fourth of the dis-
tance from the base of the egg. The eggs and the surrounding sur-
face of the leaf are dusted with waxy granules rubbed from the
body of the female. This wax is usually sufficiently abundant to
give a mealy appearance to that portion of the leaf when viewed
with the unaided eye. The eggs hatch in from four to seven days
in July. In hatching they split along the upper, concave side and
towards the anterior end; the edges of the slit do not collapse after
the emergence of the larva but continue to show the spatulate open-
ing (Fig. 36).









Fig. 36.-Egg and empty eggshell of woolly whitefly
(magnified).

The first-stage larvae (Fig. 29) are light green, with brown-
ish eyes and well-developed legs and antennae. On the dorsal sur-
face are eight conspicuous but short spines, showing white in the
figure. After crawling about for, at most, a few hours (during
which time they usually do not wander more than an inch or two
from the circle of eggs), they settle down and insert their beaks,
and like the other species of Aleurodids, do not move again until they
become adults. In the second stage (Figs. 29 and 33) a well-devel-
oped marginal fringe is present, which is longest at the posterior
end, where it is usually longer than the width of the larva. There
are also six prominent lines, of wax marking off the abdominal
segments. The dorsal spines secrete long conspicuous waxen rods,
the third pair being longest. The insect is very dark in color, al-
most black; it has, of course, lost the eyes, legs, and antennae of
the first stage. The third stage develops the woolly coat which
gives the insect its name. This stage is only a little over half
as long and two-thirds as wide as the pupa, which it otherwise
closely resembles.
The original description of the pupa by Quaintance (i) is as
follows:






Florida Agricultural Experiment Station


Size about 0.9 by 0.55 mm., subelliptical in shape. Many specimens with
more or less evident indentures on cephalo-lateral margin case, with cephalic
end obtusely pointed. Color on leaf under hand lens with secretion removed,
yellowish brown varying to blackish; under transmitted light yellowish to brown-
ish yellow. There is a distinct marginal rim all around, with wax-tubes distinct,
the incisions acute and tubes rounded distally. From margin of case all around
arises a short rim of wax, composed of individual wax threads, serrated on
margin as seen under a high power of microscope. Case usually quite covered
by a very copious secretion of grayish curling wax rods, which is very conspic-
uous on badly infested leaves, quite hiding the insects beneath. Denuded of se-
cretion, pupa case is seen at first to be almost flat, but later becoming rather con-
vex as the insect develops, with segments distinct.
Dorsum with pair of strong setae on first abdominal segment, a pair at
vasiform orifice, and a pair at caudal margin extending some distance beyond
margin of case. Vasiform orifice relatively small, subcordate, the rim dark
brown, from 6 to 8 strong setae or spines arising from caudal margin; operculum
largely filling orifice, the distal margin with two faint notches; lingula not dis-
tinguishable.

It is the author's observation that most of the black individu-
als are parasitized.
For the emergence of the adults, the pupa-case splits open in
a manner quite different from those of the other whiteflies. In-
stead of the T-shaped opening through which the adult of these
species emerges, the pupa-case of the woolly whitefly splits open
along the anterior margin, and from the apex backward there ex-
tends another rupture at right angles to the first. As the adult
pushes its way out, the four flaps thus formed flare open in a man-
ner suggesting the opening of some pods, such as that of the radish
plant.
Irr | i l rl iwr tl Tl I 9i l ""Irl"
I I II IJ II 1 1 I 1 1
I I I I II I I II I II II it II l I I I
,,- L, ^ii I II i 9.9.. I *
II II II II d II I IV |I I\I j. .,I 1I
I II i I II 1 1


I I I I i I I III I .- I II I i 1 i
II I I I J \ II I o
I I I I 1 1 i I I I1 I I I I1 I



-,'.L,, ,, 4.. L' .. 1 \ I W


Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.
Woolly whitefly.
---------------Common citrus whitefly.
................ Cloudy-winged whitefly.
Fig. 37.-Diagram showing relative date of emergence of adults.






Bulletin 126


The adults are distinctly more yellow to the naked eye than
are the adults of either of the other species. They do not carry
their wings so high over their bodies and therefore expose to view
more of the abdomen. The male is similar to the female, but a trifle
smaller.
NUMBER OF BROODS
W6 have not been able to rear this insect in the insectary and
carry it through a year as we should like to do. During the past
two years we have made the following observations in the field:

December, 1912. Adults and pupae.
May 15, 1913. Adults emerging in large numbers.
June II, 1913. Mostly in the second (some in the third) larval stage.
July II, 1913. Mostly.pupae, but some adults.
August 15, 1913. First-stage larvae, eggs and some adults.
October 1o, 1913. Adults and eggs.
October 28, 1913. First and second larval stages and some eggs.
December 4, 1913. Third-stage larvae and pupae.
February 4, 1914. Adults and eggs.
February 27, 1914. First and second larval stages.
May 21, 1914. Pupae, and third larval stage.
June 12, 1914. First-stage larvae.
June 27, 1914. Second-stage larvae.
July 14, 1914. Pupae. Adults.

From these field observations, and from the examination of
much material sent in by correspondents, we can approximately re-
construct the seasonal history of the insect. There are four gen-
erations a year, with the maximum number of adults flying during
December and January, the latter part of May, about July 20, and
about October io. The winter brood of adults is very variable in the
date of its appearance, and much prolonged. The writer found adults
to be abundant in December, 1912, in Tampa, as did S. S. Cross-
man in 1909 (5). Dr. A. E. Back (5) found them flying in January,
1910. In 1914, the maximum number of adults of the winter brood
apparently appeared about February I, in Tampa; and according to
observations of F. M. O'Byrne, at Sarasota. It should not be in-
ferred, however, that the adults are flying during the whole of
these two months; much depends upon the weather. During a cool
spell they do not emerge from the pupa-cases. It is to be noticed
that during the summer there is a brood about every ten or eleven
weeks. This period is one or two weeks shorter than that for the
common whitefly. For those adults of the winter brood that issue in
mid December, the length of time required for development is about
the same; but if emergence is delayed until February, the time is






Florida Agricultural Experiment Station


lengthened to sixteen weeks. The time between February and
May 25 is again about sixteen weeks; while for the eggs laid earlier
than February, the period is prolonged. These periods are consid-
erably shorter than those required for the development of the com-
mon citrus whitefly. This, in connection with the fact that the
woolly whitefly can develop and emerge during the winter months,
enables that species to produce four generations a year; whereas
the common citrus whitefly usually, and the cloudy-winged species
always, produce but three. The late fall brood of the woolly white-
fly nearly coincides with that of the cloudy-winged species, but the
other broods do not coincide with those of either of the other
species. (See Fig. 37.)

DAMAGE CAUSED BY WOOLLY WHITEFLY
As in the case of other whiteflies, the damage that this species
inflicts upon its host plant is of a threefold nature: (i) the with-
drawal of sap from the tree; (2) the excretion of honeydew and
the consequent growth of molds which interfere with the proper
functioning of the leaves and necessitate the washing of the fruits;
and (3) increase in the numbers of the purple scale.
I. In the case of the other whiteflies it is the second of
these injuries that attracts the attention of the grower. Neverthe-
less it is probable that the withdrawal of sap is fully as serious to
the tree as the damage resulting from sooty mold. Dr. Berger (3,
p. lvii) has shown that at a temperature of 70 degrees a million
third and fourth-stage larvae of the common whitefly exude one
pound of honeydew in 48 hours. In some measurements made by
the writer the amount of honeydew produced was found to be less
than one-tenth as much as this at a temperature of between 40 and
50 degrees F. (one and two-sevenths ounces per million pupae in
48 hours.)
Although no similar weighing have been made of the amount
of honeydew given off by the woolly whitefly, observations would
indicate that it is at least as great per larva as in the case of the
common whitefly. It is not thrown off from the body of the insect
as thoroughly as in other species, but has a tendency to cling to the
larvae, from which it hangs in large drops. This is true in even
young larvae that have not developed any great amount of woolly
coat. In older larvae the drops become entangled in the woolly fila-
ments, which still further retards the process of liberation. The
honeydew given off by this species is of a different consistency from






Bulletin 126


that given off by the common whitefly, being less watery and more
sticky. It is eagerly sought after by ants and wasps.
2. The honeydew produced by this species seems to be a less
favorable medium for the growth of the ordinary sooty mold
(Meliola camelliae) than is that of the common whitefly. There
are, however, a number of other fungi which develop in it. One
is a Meliola with much. larger fruiting bodies than those of the
common sooty mold. Another fungus is of a dirty green color,
something like the color of the common green mold Penicillium.
These and other fungi mat up an old colony of woolly whitefly
and give it a particularly dirty appearance.
3. The third aspect of the infestation, the rise of the purple
scale, is usually the most serious feature in the case of the woolly
whitefly. This phenomenon has been frequently noted with the
other citrus whiteflies and has received a variety of explanations.
Some investigations by the writer show that leaves covered with
loose-fitting sooty mold have, on the average, twice as many scales
per unit of surface as leaves free from sooty mold. The explana-
tion of this increase is as follows: The young crawlers are nega-
tively phototactic to the average degree of illumination met with
in a citrus tree, that is, they avoid such light. This leads them to
crawl into any shaded corner, as between two fruits that are in con-
tact, under the calyxes of fruits (where they are always relatively
abundant) or under loose-fitting sooty mold, and especially under
colonies of the woolly whitefly (Fig. 35). This leads to the con-
centration of crawlers in such situations. Here they are partially
protected from their enemies, such as Chrysopa larvae, or the lady-
beetles.
So marked is this tendency of the scales to congregate under
an old colony of woolly whitefly, that it is possible to tell just where
on the lower surface of a leaf there is a colony, by noting the yellow
areas on the upper surface. The writer has in many instances,
counted over a thousand purple scales per square inch in these old
colonies, not including crawlers. Five hundred adult scales, those
that have reached the egg-laying stage, have frequently been counted
per square inch. These old colonies of woolly whitefly, if suffi-
ciently numerous, become the centers from which the trees become
heavily infested with scale.






Florida Agricultural Experiment Station


HABITS
The adults are markedly more sluggish than those of the other
two species. A jar to the limb that would cause the latter to take
wing has little effect on the woolly species. So sluggish are they,
indeed, that the adults frequently .lay their eggs on the same leaf
on which they grew and emerged. There is not the marked ten-
dency to seek out the new and tender growth that is so character-
istic of the others and especially of the cloudy-winged whitefly.
They seem, indeed, to prefer leaves that have recently completed
their growth and turned dark green, to either the very young or
the very old leaves. This sluggishness greatly retards their spread
through a grove. In one of the severest infestations that have come
under the writer's notice, the woolly whitefly was confined to one-
half of a ten-acre grove. None whatever were seen at the other
side. On the other hand this same sluggishness is a distinct aid to
their transportation to a distance on the clothes of travellers and
on vehicles. The writer saw adults clinging to the clothes of the
owner of one of the above-mentioned groves after he had driven in
a buggy three miles. In Arcadia, in December, 1912, this species
was only in some trees in front of the hotel, and in a small door-
yard grove across the street; plainly suggesting that the insect had
been brought to town on the clothes or luggage of travellers. A
year later, the insect was found by Dr. Berger to be generally dis-
tributed in the groves about town, and as far out as five miles.
The crawlers of this species also are very sluggish, and settle
down very near to the place where the eggs were deposited. This
results in most of the larvae and pupae being collected in colonies,
instead of being scattered more or less uniformly over the surface
of the leaf, as with the other species. These groups or colonies
average a score or more of individuals and are strikingly charac-
teristic of the woolly whitefly.
The eggs of this species are laid in circles (Figs. 29 and 31)
which will often contain three or four rows of eggs if the female
is not disturbed during egg-laying. The female inserts her beak
into the tissue of the leaf, doubtless for feeding purposes, and, using
that as a pivot, rotates slowly about, thus making the circles.

FOOD PLANTS
The preferences of this species for different varieties of citrus
are almost the reverse of those of the other whiteflies. Grapefruit
seems to be most attractive; oranges, slightly less; while tangerines






Florida Agricultural Experiment Station


HABITS
The adults are markedly more sluggish than those of the other
two species. A jar to the limb that would cause the latter to take
wing has little effect on the woolly species. So sluggish are they,
indeed, that the adults frequently .lay their eggs on the same leaf
on which they grew and emerged. There is not the marked ten-
dency to seek out the new and tender growth that is so character-
istic of the others and especially of the cloudy-winged whitefly.
They seem, indeed, to prefer leaves that have recently completed
their growth and turned dark green, to either the very young or
the very old leaves. This sluggishness greatly retards their spread
through a grove. In one of the severest infestations that have come
under the writer's notice, the woolly whitefly was confined to one-
half of a ten-acre grove. None whatever were seen at the other
side. On the other hand this same sluggishness is a distinct aid to
their transportation to a distance on the clothes of travellers and
on vehicles. The writer saw adults clinging to the clothes of the
owner of one of the above-mentioned groves after he had driven in
a buggy three miles. In Arcadia, in December, 1912, this species
was only in some trees in front of the hotel, and in a small door-
yard grove across the street; plainly suggesting that the insect had
been brought to town on the clothes or luggage of travellers. A
year later, the insect was found by Dr. Berger to be generally dis-
tributed in the groves about town, and as far out as five miles.
The crawlers of this species also are very sluggish, and settle
down very near to the place where the eggs were deposited. This
results in most of the larvae and pupae being collected in colonies,
instead of being scattered more or less uniformly over the surface
of the leaf, as with the other species. These groups or colonies
average a score or more of individuals and are strikingly charac-
teristic of the woolly whitefly.
The eggs of this species are laid in circles (Figs. 29 and 31)
which will often contain three or four rows of eggs if the female
is not disturbed during egg-laying. The female inserts her beak
into the tissue of the leaf, doubtless for feeding purposes, and, using
that as a pivot, rotates slowly about, thus making the circles.

FOOD PLANTS
The preferences of this species for different varieties of citrus
are almost the reverse of those of the other whiteflies. Grapefruit
seems to be most attractive; oranges, slightly less; while tangerines






Bulletin 126


are distinctly least so. The writer has found this species on lemon
trees. W. L. Tower has reported them on guava in Porto Rico,
and Dr. Back (5) on mangoes at Tampa (but he states the infes-
tation to be more or less accidental).

FUNGUS ENEMIES
Both the red fungus (Aschersonia aleyrodis Webber) and the
brown fungus (Aegerita webberi Fawcett), which are such efficient
enemies of the other species, have been found on the woolly white-
fly, but usually so sparingly that they amount to very little in the
control of the insect. Only on some leaves recently received from
Palmdale, DeSoto County, has the writer seen a satisfactory growth
on material from Florida. In this case the red Aschersonia and
the brown fungus were doing efficient work. The writer has seen
a high percentage of infestation of red fungus on leaves from
Cuba where, according to Cook and Home (2) it has long been
present. A little of the red Aschersonia was found on this species
of whitefly by the writer in Tampa and Fort Myers in 1913. The
brown fungus had not been found on this species, until February,
1914, when the writer found it parasitizing the woolly whitefly at
Sarasota. When both species of whitefly are living on the same
leaf, it is usually impossible to be sure as to which species is infested,


Fig. 38.-Cladosporium growing on woolly whitefly (magnified).






Florida Agricultural Experiment Station


so thoroughly do the fungi hide the identity of their host.
In the specimens from Sarasota, however, one pupa-case was found
that had not been so thoroughly broken up by the fungus but that
it was possible to make out the angular outline of the pupa-case
of the woolly whitefly when picked off and turned over. The
pupa-case of this species is easily told from that of the others by
the prominent angles of the anterior half (Fig. 34). There is thus
no doubt about the identity of the host in this case. On the ma-
terial from Palmdale only the woolly whitefly was present.
The writer often finds a fungus belonging to the genus Clad-
osporium or a related genus, growing on dead larvae (Fig. 38).
Frequently as high as 80 per cent of the individuals in a colony
are infected. That this fungus is the cause of the death of the larvae
has not been absolutely proven. It is possible that it is only a sap-
rophyte which develops on the body of the insect after death. How-
ever, the evidence points strongly to the fungus as being the cause
of the death of the larvae. None of the infected larvae were black,
indicating that they had not been killed by the hymenopterous para-
site. Numerous cultures have been made from these dead larvae
on agar. The only fungus that came up with any degree of regu-
larity was this Cladosporium. We have had no opportunity to
try inoculation experiments on living larvae with this fungus.
Just as the common sooty mold sometimes grows on the honey-
dew which sticks to the body of the other species of whitefly, to


Fig. 39.-Eretmocerus haldemani, female (magnified).






Bulletin 126


such an extent as to kill the insects; so the several species of mold
that grow on the honeydew that clings so persistently to the woolly
whitefly, sometimes kill the latter insects also. Chief among these
are the Meliola and the green fungus mentioned above.

INSECT ENEMIES
An efficient check to the increase of the woolly whitefly is a
small wasp-like parasite, Eretmocerus haldemani by name (Figs. 39
and 40). This minute insect has a body which is less than I mm.
(one twenty-fifth of an inch) in length, and of a clear yellow color.
The compound eyes are dark brown and conspicuous under a lens,
as are also three small simple eyes between the large compound ones.
The four wings of the living insect shine with an iridescent gleam


















Fig. 4o.-Eretmocerus haldemani, male (magnified).

in the light. The female pierces the tough covering of the larva
or pupa of the woolly whitefly and lays an egg in the interior. This
egg hatches into a minute legless maggot-like larva, which devours
the contents of the whitefly pupa, grows to full size, and itself
pupates in the now empty case of the host. When ready to emerge,
it cuts a round hole in the dorsal surface of its host towards the
anterior end, through which the adult parasite emerges. This round
hole is very different in shape from the rupture which the adult
whitefly makes in emerging (see description of pupa), consequently






Florida Agricultural Experiment Station


it is not difficult, after the woolly coat has been removed, to pick
out the parasitized pupae from among those from which the whitefly
has emerged. These parasitized pupa-cases usually turn jet black,
which further helps to distinguish them. This is not always the
case, however. Occasionally one finds a pupa-case that, although
showing the emergence hole of the parasite, has the brown color of
the normal pupa-case. On the other hand some pupa cases turn
black without ever showing the exit holes of the parasite. In some
cases this may be due to the parasite having died in the process of
development; but in other cases very young larvae assume the black
color.
These black pupa-cases with the round holes were observed and
recognized as the work of a hymenopterous parasite some time be-
fore the parasite itself was captured (9). This parasite (Eret-
mocerus haldemani) was first found in Florida by the writer. It
was captured at Lakeland in May, 1913, when the hosts were in
an advanced stage of development. The parasites were again seen at
Winter Haven on October 29, when most of the whitefly larvae
were in the first and second stages of development.
According to Dr. Howard, who described it, this parasite has
before been found only in California and Mississippi, in both cases
parasitizing aleurodids. It would seem, then, that the species is a
widespread one, and is doubtless native to Florida, where it has
been parasitizing some one of our native whiteflies. When the
woolly whitefly was introduced, the parasite quickly discovered it
and commenced to breed on it. The parasite probably occurs in
Cuba as well, where it helps to keep its host in check; as Dr. Back
mentioned finding pupa-cases with the exit holes of a hymenopterous
parasite.
It is a fortunate thing for the orange growers of Florida that
there was a native insect ready to infest the woolly whitefly upon
its arrival here; otherwise, it might have become an exceedingly
destructive pest because of its ability to spread rapidly over the
State, and because of its exceedingly sticky and copious honeydew,
and its comparative immunity to the attacks of the fungi which
parasitize the other whiteflies.
The original description of Eretmocerus haldemani as it ap-
peared in the Proceedings of the Entomological Society of Wash-
ington, Vol. X, p. 65, is as follows:
FEMALE.-Length, 0.64 mm.; expanse, 1,78 mm.; greatest width of fore
wing, 0.32 mm. Antennal club more than four times as long as pedicel, not
ellipsoidal as with E. califonnicus, but approaching the oar-shape figured by







Bulletin 126 99

Haldeman for E. corni and lacking the longitudinal lines found abundantly on
the club with E. californicus; antennae as a whole about as long as entire body.
Mesoscutum and mesoscutellum with a wide delicate irregular subhexagonal
sculpture, the scutum in addition being faintly granular. (In E. californicus the
surface of these sclerites is faintly aciculate.) General color lemon-yellow,
eyes reddish, ocelli crimson, legs pallid, flagellum of antenna yellowish.
MALE.-Resembles female except for usual sexual differences.

PERCENTAGE OF PARASITIZATION

Beginning early in 1912, some careful determinations were
made of the percentage of parasitized individuals in colonies from
different places. The number of parasitized individuals was de-
termined by removing the woolly coat from the pupae and looking
for the exit hole of the parasite. In many cases it was necessary to
remove the insect and examine it under a microscope in order to
be certain that it was not parasitized. The results of these counts,
taken in part from the annual report for 1913, are given in Table I.


TABLE I.

PARASITIZED WOOLLY WHITEFLY.









JM. Baker's grove, Tamp Feb. I, 1912 oo 68 4 18
Locality March 1, 1 1

P g M 20 72 2



Winter Haven Dec. 9, 1913 19 26 5 58 II
Sarasota Feb. 26, 191 330 79 21 ... f
Tampa Bay Hotel grounds- Jan. 31, 19121 400 98 ------ ------ 2

J. M. Baker's grove, Tampa Feb. I, 191 2 6 oo 68 314 18
Tampa Bay Hotel -------March 12, 1912 8s 87 ----- 13 --
Aman's grove, Ybor City. March 12, 1912 86 6g 12 20
St. Petersburga -------- March 14, 1912 220 72 2 26
Lakeland -----------Oct. 29, 1913 39 51 15 33 ---
Winter Haven ----- Dec. 9, 1913 190 26 5 58 4
Sarasota ------- eb. 26, 1914 330 79 21 8 o

Wauchula --------------May 21, 1914 524 -------- 6 39 --





Palmdale Sept. 24, 1914 78 5 5 37 --53
Tampa ------- ----- June 12, 1914 2120 2 2 ------ 20 --
Wauchula -- ------ June 1914 528 o--- 1 87
Nocatee ----------------une 27, 1914 452 ----- 28 6o 12
Winter Haven -----J-----July 14, 1914 483 --------- 45 13 42
Sarasota ----------------July 14, 1914 367 ------ 28 io 62
Clearwater -------------July, 19141 255 ------------ 8o 20 --
Lakeland -__---------_---- Sept. i, 1914 200----------_ 95 5 --_
Palmdale ---------------Sept. 14, 1914 78 5 5 37 53
Avon Park ------------ Oct. 16, 1914 850 28 21 40
Palmdale -------------- Nov., 1914 500 50 40 10o






Florida Agricultural Experiment Station


SPREAD OF WOOLLY WHITEFLY IN FLORIDA
Detailed accounts of the spread of an introduced insect fur-
nish valuable data to the entomologist, and are so few that each
such account is valuable. The data for the following accounts are
taken from the field observations of the writer and from material
sent in for identification. Each locality and date is authentic, being
substantiated by specimens. In localities that have been included,
the date is that of the collection of the material; the establish-
ment of the infestation, was in every case, some time previous, at
least as early as the immediately preceding date of the emergence
of adults. I believe that the account is fairly complete for this
species. The colonies are so conspicuous that they are likely to
attract the attention of a grower soon after introduction; and some
grower in that community, finding a new insect on his tree, is apt
to send it to the Experiment Station.
The woolly whitefly was first found in Tampa in November,
1909 (4). When the writer took up the study of this insect in
February, 1912, it was spread all over Tampa and Ybor City. It
occurred in the R. S. Wilder grove, on the Sulphur Springs street-
car line; but it was not general in the groves in this neighborhood.
It occurred also at Lake Magdalene, seven miles west. It was in
one grove in Limona, and in Lakeland at the corner of S. Massa-
chusetts Avenue and Lemon Street. It was found in a few door-
yard trees in St. Petersburg, but not in large groves outside the
town. In June, 1912, it had spread to Terra Ceia and Palmetto,
and was found in some of the larger groves about Lakeland, a few
miles from the town. In December an incipient infestation was
found in the hotel grounds at Arcadia and in a dooryard grove
diagonally across the road, but not in other groves about the town.
In April, 1913, it appeared at Florence Villa and Winter Haven,
and in May, at Alva (Lee County), and in Orlando. In June we
had it from Wulfert, Largo, and Auburndale. In August it had
spread to other groves in Largo, and in September, 1913, it appeared
at Wauchula, Bradentown and Sarasota; while at Arcadia it had
reached groves 7 miles from town. In February, 1914, it had reached
Fort Ogden, and in March, Ritta, on the south shore of Lake Okee-
chobee in Palm Beach County. In July, 1914, we had it from Avon
Park. (Whether this insect had spread overland from Wauchula
or come down the railroad, it was impossible to say.) In Septem-
ber, we received it from Palmdale in the southeastern part of De
Soto County, and in November from near Dade City in Pasco






Bulletin 126


County. It is to be noticed that, with two exceptions, all the com-
plaints that have reached us, have come in the spring and early
summer. Two of the records in September, 1913, and one in Decem-
ber, 1912, were not direct complaints from the owners, but were
small infestations discovered by the writer, or by E. W. Berger
in the course of his duties as nursery inspector.
That this whitefly should extend its limits, especially in the
spring, is in full accord with the fact that its numbers are greater
in the spring because of the inactivity of its parasite during the
winter. The woolly whitefly is distinctly a spring pest. As to its
manner of spread, this would seem to be, even more than in the case
of the other whiteflies, brought about by the accidental carrying of
the adults from place to place. All the incipient infestations I have
seen would point to this conclusion, as also the observation of one
insect carried for three miles on the clothes of a grove owner. The
woolly whitefly usually makes its first appearance in the grove about
the house or barn, and its first appearance in a town is usually about
the hotels and business centers, as was observed in Lakeland, Ar-
cadia and St. Petersburg. A study of the distribution shows that
this insect has spread most rapidly along lines of commerce, as rail-
roads and steamboat lines. In one of the groves at Lakeland where
it did the most damage, the first infestation was not about the house
or barn, but on the side of the grove near the railroad. The writer
has found no evidence of the woolly whitefly being spread by means
of nursery stock; indeed, if such stock is properly defoliated, the
transportation of the woolly whitefly by such means would be im-
probable. Wind has been a much less important factor in the dis-
tribution of this whitefly than in the case of the common citrus
whitefly, because of its sluggishness. Doubtless the absence of suit-
able wild host plants has hindered its spread through infested com-
munities.
The writer's thanks are particularly due to Dr. L. O. Howard
for the identification of the parasite (Eretmocerus haldemani) ; also
to A. C. Mason and U. C. Loftin for much of the work in de-
termining percentages and the taking of photographs; to Prof. H.
E. Stevens for identification of some of the fungi; and to F. M.
O'Byrne for collecting some of the material and field notes. The
part of Fig. 37 that shows the curves for the other species has been
taken with some modifications from Morrill and Back (6).






102 Florida Agricultural Experiment Station

REFERENCES.

I. QUAINTANCE, A. L.-U. S. Dept. of Agr., Bur. of Ent., Tech. Bul. 12, Pt.
5. 1907.
2. COOK, M. T., and HORNE, W. T.-Estacion Central Agr. de Cuba, Bul. 9.
I908.
3. BERGE, E. W.-Fla. Agr. Exp. Sta., Rept. for 9go8. 19o9.
4. BACK, E. A.-Florida Fruit and Produce News. Nov. 26, 1909.
5. BACK, E. A.-U. S. Dept. of Agr., Bur. of Ent., Bul. 64. Pt. 8. 19Io.
6. MORRILL, A. W., and BACK, E. A.-U. S. Dept. of Agr., Bur. of Ent., Bul.
92. 191I.
7. BERGER, E. W.-Fla. Agr. Exp. Sta., Rept. for 1911. 1912.
8. BACK, E. A.-Canadian Entomologist, 44. Pt. 5. May, 1912.
9. WATSON, J. R.-Fla. Agr. Exp. Sta., Rept. for 1912. 1913.
io. YOTHERS, W. W.-U. S. Dept. of Agr., Bur. of Ent., Circular 168. 1913.
11. WATSON, J. R.-Fla. Agr. Exp. Sta., Press Bul. 212. 1913.
12. YOTHERS, W. W.-Florida Grower. Aug. 23, 1913.
13. WATSON, J. R.-Florida Grower. Dec. 6, 1913.
14. WATSON, J. R.-Fla. Agr. Exp. Sta., Rept. for 1913. 1914.
15. QUAINTANCE, A. L.-U. S. Dept. of Agr., Bur. of Ent., Tech. Bul. 27-II.
Classification of Aleurodidae, II. 1914.




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