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 Title Page
 Credits
 Character of damage done
 Varieties attacked
 Host plants
 Identifying the aphids
 Means of spread
 Enemies
 Control measures
 Life history
 Relation of ants to the aphids














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 174
Title: Controlling the citrus aphis (Aphis spiraecola Patch)
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 Material Information
Title: Controlling the citrus aphis (Aphis spiraecola Patch)
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 174
Physical Description: Book
Language: English
Creator: Watson, J. R.
Beyer, A. H.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1925
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Bibliographic ID: UF00027600
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 79
    Credits
        Page 80
    Character of damage done
        Page 81
    Varieties attacked
        Page 82
    Host plants
        Page 83
        Page 84
    Identifying the aphids
        Page 85
    Means of spread
        Page 86
    Enemies
        Page 86
        Page 87
        Page 88
        Page 89
    Control measures
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
    Life history
        Page 95
    Relation of ants to the aphids
        Page 96
Full Text


March 10, 1925


UNIVERSITY OF FLORIDA
Agricultural Experiment Station



CONTROLLING THE CITRUS APHIS
(Aphis spiraecola Patch)

By
J. R. WATSON AND A. H. BEYER


'I

Fig. 48.-Foliage curled as a result of citrus



Bulletins will be sent free upon application to the
GAINESVILLE, FLORIDA


aphis damage.



Experiment Station,


Bulletin 174







BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN, Citra
J. C. COOPER, JR., Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee

STATION STAFF
WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT, B. S., Vice Director and Animal Industrialist
J. R. WATSON, A. M., Entomologist
R. W. RUPRECHT, Ph. D., Chemist
0. F. BURGER, D. Sc., Plant Pathologist
G. H. BLACKMON, B. S. A., Pecan Culturist
W. B. TISDALE, Ph. D., Associate Plant Pathologist, Tobacco Ex-
periment Station (Quincy)
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. FRANCIS COOPER, B. S. A., Editor
J. H. JEFFERIES, Superintendent Citrus Experiment Station
(Lake Alfred)
A. H. BEYER, M. S., Assistant Entomologist
C. E. BELL, M. S., Assistant Chemist
W. E. STOKES, M. S., Grass and Forage Crops Specialist
J. M. COLEMAN, B. S., Assistant Chemist
HAROLD MOWRY, Assistant Horticulturist
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. F. CAMP, Ph. D., Assistant Plant Pathologist
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
GEO. E. TEDDER, Foreman, Everglades Experiment Station
(Belle Glade)
RUBY NEWHALL, Secretary
A. W. LELAND, Farm Foreman
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. G. KELLY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
IDA KEELING CRESAP, Librarian
ROBERT E. NOLEN, B. S. A., Lab. Asst. in Plant Pathology
H. E. BRATLEY, B. S. A. E., Asst. in Entomology
MARY E. ROUX, Mailing Clerk

K. H. GRAHAM, Auditor
RETTA MCQUARRIE, Assistant Auditor









CONTROLLING THE CITRUS APHIS
(Aphis spiraecola Patch)*
By J. R. WATSON AND A. H. BEYER
In the spring of 1924 there appeared in the southwestern
part of the citrus belt a severe outbreak of aphids. The insect
was at first confused with the melon aphis (Aphis gossypii)
which always appears in small numbers on citrus during the
spring of the year. But by April it was recognized that the
growers had to contend with a new pest of major importance.
From the original focus the insect spread with surprising
rapidity and by the end of June had covered most of the citrus
belt. By September it reached St. Johns County and was pres-
ent also in extreme western Florida, on satsumas. With the
advent of the rainy season in June the outbreak subsided, altho
there continued to be more or less aphids about.
Between the last week of October and Christmas very little
rain fell in the citrus belt, the trees put out very little new
growth and the aphis nearly disappeared from most groves,
completely so from some. But warm weather following ample
showers caused much new growth during January, and now
(March 1) it seems likely that there is to be another severe in-
festation. To help the growers meet the threatened outbreak
by presenting our experience in control and such facts concern-
ing the life history of the aphis as will make the intelligent ap-
plication of control measures possible, is the object of this bul-
letin. In a later bulletin the authors hope to present a more
detailed account of the research work connected with this aphis.

CHARACTER OF DAMAGE DONE

The citrus aphis attacks the very young leaves, twigs, blos-
som buds, blossoms and young fruit. In a very heavy infesta-
tion the twigs are attacked when they first push out from the
matured growth. Often this twig is prevented from growing
at all. A button only a fraction of an inch in length may be so
severely attacked by the aphids that it never develops further.
If the aphids are later in reaching the twig, or the infestation
is not so severe, the twig may make a fair growth, but the
*This aphis is clearly related to Aphis pomi, the green apple aphis of
the North, and may be identical with that species. If so, Aphis pomi is
the proper name.






Florida Agricultural Experiment Station


leaves will be curled. The extent of the curling will depend on
the age of the leaf, when attacked, and the number of aphids
present. The leaves are very frequently twisted into a tight
spiral suggesting a snail shell. (See fig. 48.) The formation of
these spirals is one of the things that makes the aphis so hard
to control, as those inside the curled leaves are very hard to
reach with any insecticide. In the case of very young leaves
a single aphis is often sufficient to cause this curling.
When the blossom buds and blossoms appear they are at-
tacked and, if the infestation is heavy, they will be so severely
injured that the blossoms and young fruit will fall. A heavy
infestation of aphids materially reduces or entirely prevents the
setting of fruit. Less severely injured fruit may be able to sur-
vive the attacks of the aphids but will be full of little bumps
or swellings. As the fruit matures it will to a considerable ex-
tent outgrow this unevenness but it will never be as smooth as
uninjured fruit.
The curling and dwarfing of the leaves and twigs seriously
interferes with their function, and if every flush of growth as
it comes out suffers in this manner the tree will be badly
stunted and may be killed outright.
Another injurious result of the curling of the leaves is the
fact that the spirals make excellent hiding places for purple
scale crawlers. In these tightly curled leaves they can develop
and it is almost impossible to reach them with any contact in-
secticide. The young scale crawlers crawl away from strong
light and seek shade. This reaction of the scale crawlers to
light causes them to congregate in such shaded places as the
curled leaves, and they are able to develop there safe from any
oil emulsion sprays. This is a serious matter in the control of
purple scale in groves.
The new citrus aphis cannot live on mature citrus foliage or
twigs, and many aphids born on this hardening foliage develop
wings and fly away. The stage of growth at which they leave
depends largely on the succulence of the twigs and stems, but
ordinarily a citrus leaf is not attacked after it is two-thirds
grown.

VARIETIES ATTACKED
The new citrus aphis seems to show a decided preference for
citrus of the Mandarin species, if it is in the proper stage of
growth. After the Mandarin group,, round oranges, lemons and







Bulletin 174, Controlling the Citrus Aphis


limes are perhaps the second choice, and probably the third
choice would be the sour orange. Grapefruit is troubled very
little, and to all practical purposes is immune to the aphids.
With the different varieties of any species the stage of growth
seems to be the important factor. Varieties that start into


Fig. 49.-The curled foliage on the new growth of this old tree cut back
for rebudding is typical citrus aphis injury.

growth early have been found to be most affected. Varie-
ties that are in active growth when the maximum number of
aphids are about suffer more than those that are more dormant
at that time. In all cases it is the young trees that suffer most
because of their more continuous growth.

HOST PLANTS

The native plant of this insect is, according to present
indications, the genus Spiraea, belonging to the rose family.
One of the most common of these plants in Florida is the bridal







Florida Agricultural Experiment Station


wreath, Spiraea prunifolia. The behavior of the aphis on spi-
raea is quite different from that on citrus it that it can feed
on the mature leaves and does not require new growth. In ad-
dition to feeding on this plant thru the winter when there is no
new growth on the citrus, the aphis has been observed by mem-
bers of the United States Bureau of Entomology at Orlando,
to lay eggs on this plant. The only other plants on which the
aphis has been observed to lay eggs in Florida are Pyrus delu-
taefolia and the Japanese Flowering quince, both rare plants' in
this state.*
In many sections of the state, including Gainesville, spiraea
was the only plant on which this aphis was found during the
months of December and January. Undoubtedly in many sec-
tions, particularly in the northern part of the citrus belt, it is















Fig. 50.-Winged female aphis. (Highly magnified.)
spiraea that enables the aphids to live over winter when there
is no new growth on the citrus trees.
These facts make spiraea a very dangerous plant in citrus
communities. We cannot too strongly recommend that the
growers destroy spiraea thruout the citrus belt. There have
been extensive plantings of spiraea around postoffices in many
towns in Florida, and it is possible that this has been the origin
of the aphis in the state.
The aphis has been observed on a number of other host plants
but these seem to be decidedly of a secondary nature and prob-
*The eggs were found by the junior author from early December to
late January.







Bulletin 174, Controlling the Citrus Aphis


ably are of minor importance. Among such minor host plants
are the following: milkweed, cudweed, Crataegus, dogfennel,
Jerusalem oak, nightshade, wild plum, sand pear, loquat; and
the garden plants lettuce and peppers.

IDENTIFYING THE APHIS
There are three species of aphids common to citrus in Flor-
ida. One of the most widespread, and up to two years ago the
most common, is the melon aphis, Aphis gossypii, so called from
the fact that it is most com-
mon and destructive on mel-
ons in this state. It was first
known as a cotton pest. The
new citrus aphis can be dis-
tinguished from the melon
aphis by both its appearance
and the character of its work.
Altho there is a darker col-
ored phase, the new citrus
aphis is usually a light green
thruout its nymphal life, a
shade of green almost iden-
tical with that of the citrus Fig. 51.-Wingless female citrus aphis.
leaf. The very young melon (Highly magnified.)
aphids are much more yellow than citrus aphids, but the
later stages are decidedly darker, a dark olive green, some-
times almost slaty in color. When the new citrus aphis
passes into the pupal stage and the prominent wing pads are
formed the head and thorax turn an amber brown, whereas the
abdomen retains the bright green color of the nymph. The eyes
are dark red, antennae, wings and legs whitish. The color of
the winged adults is similar. In the case of the melon aphis the
thorax and abdomen usually remain the same in color, dark
olive green. The entire cornicles (honey tubes) are dark,
whereas in the melon aphis the tips only are dark.
The melon aphis does not ordinarily curl up the leaves in such
a tight spiral as does this species. It has more of a tendency
to infest the twigs as well as the leaves and will continue to
feed on the leaves and twigs until they get much more mature
than is the case with' the present aphis.
The third species usually found in citrus groves is Toxoptera







Florida Agricultural Experiment Station


aurantiae, a bright yellow insect which usually occurs in dense
colonies on the twigs as well as the leaves. It is not common
enough to be much of a factor in the citrus industry, and un-
like the new aphis, occurs most frequently on grapefruit trees.
Another aphid sometimes met with on citrus trees is the com-
mon garden aphis Myzus persicae. In color this resembles the
citrus aphis but it is much smaller. Confusion of this species
with the new citrus aphis is responsible for many reports of the
new citrus aphis feeding on vegetables and weeds.
Other characters of the new citrus aphis which would differen-
tiate it from the melon aphis are
its greater tendency to form
wings, and the comparative scar-
city of the spherically swollen
individuals which have been
parasitized by the wasp-like en-
emy.
MEANS OF SPREAD
All indications are that the
new citrus aphis spreads over
Florida almost entirely by means
of flight. Its spread was not
Fig. 52.--Last stage nymph or most rapid along lines of com-
"pupa." (Highly magnified.) munication, as is always true in
the case of insects which are distributed by man from one place
to another. For instance, the aphis appeared in St. Lucie
County before it did in Seminole, whereas the means of com-
munication between Polk, Hillsborough and Seminole counties
are much greater.
As the growth on which they are living matures, many of the
aphids born under these conditions develop wings and move out
in all directions, usually with the wind prevailing at that time.
There is no evidence that they have to any great extent been
carried by autos, trains, or transported on nursery stock. The
immense numbers and short generations have enabled the in-
sect to spread with surprising rapidity over citrus Florida.

ENEMIES

All aphids, in Florida as well as in other places, are subject to
the attacks of numerous enemies.







Florida Agricultural Experiment Station


aurantiae, a bright yellow insect which usually occurs in dense
colonies on the twigs as well as the leaves. It is not common
enough to be much of a factor in the citrus industry, and un-
like the new aphis, occurs most frequently on grapefruit trees.
Another aphid sometimes met with on citrus trees is the com-
mon garden aphis Myzus persicae. In color this resembles the
citrus aphis but it is much smaller. Confusion of this species
with the new citrus aphis is responsible for many reports of the
new citrus aphis feeding on vegetables and weeds.
Other characters of the new citrus aphis which would differen-
tiate it from the melon aphis are
its greater tendency to form
wings, and the comparative scar-
city of the spherically swollen
individuals which have been
parasitized by the wasp-like en-
emy.
MEANS OF SPREAD
All indications are that the
new citrus aphis spreads over
Florida almost entirely by means
of flight. Its spread was not
Fig. 52.--Last stage nymph or most rapid along lines of com-
"pupa." (Highly magnified.) munication, as is always true in
the case of insects which are distributed by man from one place
to another. For instance, the aphis appeared in St. Lucie
County before it did in Seminole, whereas the means of com-
munication between Polk, Hillsborough and Seminole counties
are much greater.
As the growth on which they are living matures, many of the
aphids born under these conditions develop wings and move out
in all directions, usually with the wind prevailing at that time.
There is no evidence that they have to any great extent been
carried by autos, trains, or transported on nursery stock. The
immense numbers and short generations have enabled the in-
sect to spread with surprising rapidity over citrus Florida.

ENEMIES

All aphids, in Florida as well as in other places, are subject to
the attacks of numerous enemies.







Bulletin 174, Controlling the Citrus Aphis


Some of the most important in keeping in check the new cit-
rus aphis are the larvae of syrphus flies. These are soft-bod-
ied, legless grubs, dull yellow in color with conspicuous black
and brown markings. When full grown these larvae are about a
third of an inch long. The adults which lay the eggs from
which the larvae hatch are two-winged flies with very slender
bodies resembling somewhat wasps in appearance.
These flies have the ability to hover over blossoms and colonies
of aphids as does a humming bird or a hawk moth over a flower,
by a rapid vibration of the wings they can remain stationary in
the air. When disturbed they dart very quickly from one place
to another. Most of them are small, measuring less than an
inch across the wings when outspread. Eggs are laid on the
leaves among the aphids. They are small glistening white
bodies, much longer in proportion to their width than a hen's
egg.
The flies can be seen hovering around a colony of aphids in
the middle of a bright sunny day even in mid-winter. So far,
four species have been identified as feeding on the new aphis.
They often become very common in aphid colonies and are of
major importance in controlling the insect. The larvae impale
an aphid on the end of their beaks and lift it into the air, suck-
ing the juices in a manner suggesting a man drinking from a
jug. After absorbing the liquids from the aphid, they discard
the carcass and attack a new one.
Other important enemies of aphids are lady beetles. Five
species have been observed feeding on the citrus aphis. In the
probable order of their importance they are the Convergent, the
Blood Red, the Twice Stabbed. the Two Spotted, and the Austra-
lian lady beetle. In the case of the first two species aphids form
the most preferred diet. The Twice Stabbed and the Two
Spotted feed by preference on the crawlers of scale insects and
are of minor importance in the control of aphids.
This is the first time the Australian lady beetle has ever been
known to feed on anything other than cottony cushion-scale and
other Australian lady beetles. Just how much of a factor in
the control of aphids the Australian lady beetle will be is prob-
lematical. Lady beetles, unlike syrphus flies, feed on aphids in
both the adult and larval stages. Adult lady beetles are much
more conspicuous than the larvae of the syrphus flies and are
more apt to be noticed by the growers, but an actual count 'd







88 Florida Agricultural Experiment Station

numbers on a leaf will usually show more syrphus flies than lady
beetles.
Other common enemies of aphids are aphis lions. These are
the larvae of lace-winged flies, insects with four very delicate
transparent wings, which are frequently seen around citrus
trees. The larvae are provided with long sickle-like jaws with
which they pierce the bodies of aphids and feed on the juices.
Fuller information on aphis lions may be found in Bulletin 148
of this Station.
A very common enemy of the melon aphis is a wasp-like in-
sect which lays its eggs in the bodies of the aphids. From these
eggs a grub hatches out which feeds at first on the fatty tissues





S' 0














Fig. 53.-Predaceous enemies of the citrus aphis.
of the aphids but finally attacks the vital organs and kills them.
Affected aphids swell to several times their natural size and be-
come nearly spherical in shape. The grub pupates in the dead
aphid and when the adult wasp gets ready to emerge it gnaws
a circular hole in the top of the abdomen of the aphid thru
which it emerges. These swollen aphids with the circular holes
are very common sights in colonies of the melon aphis and the
parasite is one of the important factors in keeping the melon
aphis from becoming much of a pest on citrus.







Bulletin 174, Controlling the Citrus Aphis


The relation of this parasite to the new citrus aphis is pecu-
liar. In many colonies of aphids one can observe swollen indi-
viduals of a rich red brown color. These when dissected almost
invariably show the presence of a grub inside. As the aphids
get older and die the body wall usually collapses to some extent,
and an aphis dissected at this time usually shows a dead grub
inside.
Apparently the hymenopterous parasite lays its eggs in the
new citrus aphis and the grub develops and kills the aphis, but
for some reason or other it is unable to emerge. This may be
due to the fact
that there is not
enough food in
the body of the
citrus aphis. The
volume of the
citrus aphis is i
only about two-
thirds that of the
melon a p h i s.
Last year not a
single citrus
aphis was found
in which there
were any emer-
gence holes of
the parasite, but
this year a few
such individuals
have been seen.
It is to be hoped
that this para-
site is gradually Fig. 54.-A good home-made mixer for mixing
adapting i t s e 1 f nicotine sulphate with hydrated lime. Mate-
rials needed to construct it are: A 50-gallon
to the new citrus barrel, four %-inch pipes 10 inches long, 2 el-
aphis, but up to bows and 2 brackets.
the present time at least, it has not been a factor in controlling
the new aphis.
Fungous Enemies. At least one species of fungus (Ento-
mophthora sp.) has been observed parasitizing the aphis. This
.causes the aphis to turn reddish brown in color. This fungus







Florida Agricultural Experiment Station


was one of the most, and perhaps the most important factor in
checking the outbreak during the summer of 1924. Due to the at-
tacks of this fungus and the more rapid breeding of its other
enemies the aphis was almost completely controlled during the
summer and fall of last year. However, there were always
enough left to start an infestation.
But as the dry cool weather of the winter came on this fun-
gus became very much less in evidence. In other words .the
seasonal activity of this fungus seems to be very similar to that
of other entomogenous fungi which are so important in control-
ling whiteflies and scale-insects during the rainy season. We
apparently have little to fear from the citrus aphis during the
rainy season.

CONTROL MEASURES

Spot Dusting. As the aphids do the most damage in the
early spring when the flush of growth comes on and blossoms
are unfolding and fruit setting, it is important to delay as long
as possible a general infestation of the grove. For this purpose
spot dusting is very important. As soon as growth starts on
any trees in the spring (it will usually start first on young
trees), the grove should be inspected once or twice a week, or
oftener as the weather gets warmer, and any infested trees or
parts of trees should be thoroly dusted. This is best done in the
middle of the day when the temperature is high. At that time
the poisons in the dusts will volatilize more quickly and the kill-
ing will be greater.
For this spot dusting the Station has used chiefly 3 percent
nicotine sulphate-lime dusts. These can be purchased from any
of the larger insecticide houses of the state, or the growers can
make their own dusts at a saving of half the cost. For this
purpose take a 50-gallon barrel and attach flanges or unions
one on each side and into the unions screw pieces of ll/4-inch
pipe. A rectangular hole about 8 inches square is cut in one end
of the barrel. This hole is hinged with a door which is kept
closed by a simple clasp or cleat, and the edges of the door are
padded to prevent leakage. The barrel should then be sus-
pended in a frame similar to a barrel churn so that it will ro-
tate freely.
Then place in the barrel several dozen small stones or pieces
of brick about two inches in diameter. Next put in the barrel







Bulletin 174, Controlling the Citrus Aphis


50 pounds of the best grade of hydrated lime and pour over the
surface of this as uniformly as possible 31/2 pounds of nicotine
sulphate. The door is then closed and fastened and the barrel
rotated for about five minutes at the rate of about 30 revolu-
tions per minute. (See fig. 54.)
For spot dusting the best instrument is probably a knapsack
duster of the bellows type. This gives intermittent puffs of
dust rather than a steady current, and there is less waste of
material and effort than in the case of machines that give a
steady current. A good bellows duster also throws the dust
with greater force than those supplying a steady stream.












Fig. 55.-Tenting trees in preparation for applying calcium cyanide dust
for the citrus aphis.

Calcium cyanide has been used extensively in the state for
this spot dusting with apparently good results. (See fig. 55.)
Dipping. On very young trees the infested twigs may be
dipped in a contact insecticide. This is done by placing the insec-
ticide in a bucket and going thru the grove and bending the in-
fested twigs over and dipping them into the solution. This
method, tho slower than dusting, insures a very thoro kill if
painstakingly done. Any good contact insecticide will serve for
the purpose of dipping. A tablespoonful of nicotine sulphate
and a few tablespoonfuls of soap to a bucket of water will
answer very well, or one can use a good strong solution of soap
alone. Infested twigs that cannot be bent over should be cut
off and dropped into the insecticide, or they can be washed
with a sponge.
Where a heavy infestation of purple scale develops in the
curled leaves pruning is the most thoro way to get rid of it, as
it is very difficult indeed to reach the interior of these leaves







Florida Agricultural Experiment Station


with" any spray. Some growers have adopted the practice of
sending a man thru the grove with a picking bag, and the in-
fested twigs are cut off and dropped into this bag. This, however,
is about as slow as dipping and has the further disadvantage of
the loss of growth. In the case of badly curled growth, how-
ever, which the owner wishes to discard, this makes a conven-
ient method of dealing with the aphis.
Spraying. When the infestation of the grove becomes quite
general so that it is necessary to treat every tree, one may
either dust his entire grove with a power duster with the nico-
tine sulphate-lime dust mentioned above, or he may spray the
grove.
Nicotine sulphate-lime dusts are of course expensive when
applied to an entire grove and where possible, spraying should
be substituted for it. If spraying is done early in the season
before there is much new growth, open blossoms and young
fruit on the trees, one can use oil emulsions without much
danger of burning. At this time the. temperature is usually low
and if the oils are properly made and care is taken the burning
will not be severe. After any considerable number of blossoms
open and the fruit begins to set, spraying with the common oil
emulsions will have to be discontinued as the danger of burning
the young foliage will be too great.
Spraying has the added advantage that it will also help to
control scale-insects and whitefly.
In the case of a few trees around the door yard where one has
good water pressure, the hose may be turned on with all the
pressure the young foliage and blossoms will stand. This will
wash off a good many of the insects, and if repeated several
times a week will probably be an efficient means of control.
Combination Sprays and Dusts. In many cases it will be pos-
sible to combine the control of the new citrus aphis with the
control of other pests and thus greatly reduce the cost of control
measures. We have already mentioned the possibility of spray-
ing with an oil emulsion for the control of this pest and whitefly
and purple scale.
In the case of oranges of the Mandarin type where it is de-
sirable to spray for scab the addition of 1 part of nicotine sul-
phate to 800 parts of Bordeaux will render the solution very
effective against the aphids and not harm it in the least as a
fungicide.
The same is true of spraying round oranges for melanose.







Bulletin 174, Controlling the Citrus Aphis


Since grapefruit is not ordinarily troubled with the citrus aphis
it probably would not be worth while to add the nicotine sul-
phate to the scab and melanose spray on grapefruit.
Another insect, control measures for which can readily be
combined with those for the citrus aphis, is thrips. Thrips oc-
casionally get sufficiently abundant in the bloom of citrus trees
to considerably shorten the crop and mar the young fruit. Cir-
cumstances under which spraying for thrips will ordinarily
pay have been discussed in Bulletin 168. If the citrus aphis
is present the same solution recommended for thrips will kill
all aphids hit, as aphids are more easily killed than thrips by
contact insecticides.
In some cases it will be practical to combine the control of the
citrus aphis with that of rust mites and red spiders. For this



















A. ..... -
Fig. 56.-Applying the calcium cyanide dust with a dust gun.
purpose it will be necessary in order to do efficient work to add
nicotine sulphate in the solution ordinarily used for rust mite
and red spiders. To each 100 gallons of lime-sulphur solution
add 1 pint of nicotine sulphate. If it is desired to use a dust to
control rust mite, a combination dust for rust mite and citrus
aphis can be secured by adding 10 to 15 percent of sulphur in
the nicotine sulphate-lime dust. Many of the insecticide houses
are supplying nicotine sulphate-lime dust and also cyanide dusts







Florida Agricultural Experiment Station


with a considerable percentage of sulphur for this purpose. The
addition of the sulphur makes the dust somewhat heavier and
more difficult to use in the machine.
Fall Treatment of Groves. Experiences during the past win-
ter have made very plain the treatment a.grove should receive
during the fall and winter to minimize the gravity of the aphis
situation. Since the aphis can feed on nothing but tender foli-
age, if it is possible to throw the grove into complete dormancy,
the aphis, as far as our present knowledge and experience indi-
cates, will be entirely exterminated, as it has not been known to
lay any eggs on citrus. Groves which were kept completely dor-
mant during last fall and early winter were exceptionally free
from aphids by the first of February and the infestation devel-
oped but slowly during the succeeding weeks.
To keep the grove dormant during the fall, cultivate as little
as possible after the rainy season. If the weeds become too rank
use the mowing machine rather than the harrow if possible. Cut
down the fall fertilization, particularly applications of ammonia,
to the lowest point compatible with the welfare of the trees. It
is better to starve the trees a little in the fall than to have an
infestation of aphids in the spring. Then when growth does
start in the spring in spite of one's efforts, do everything pos-
sible to rush it along. Begin cultivation and fertilize liberally,
using as large amount of nitrate of soda as possible, bearing in
mind that too much is apt to throw the trees into dieback.
If this treatment can be given a grove it should practically
free it of aphids at the beginning of the flush of growth, and by
rushing the growth along most of it should be out before the
aphids get abundant enough to do very much damage. Aphids
that do appear can be spot dusted according to the above direc-
tions.
Relation to Truck Crops. It has been observed that where
truck crops have been raised near the trees during the winter
there are more parasites of the aphid than in other groves. The
reason is plain. On the truck crops other aphids develop, in-
cluding the garden aphis, cabbage louse, pea aphis, melon aphis,
etc. These aphids being present in the winter time are attacked
by parasites and predators, which are therefore present to at-
tack the citrus aphis when it appears. For this reason the Ex-
periment Station has advised the planting of truck crops in or
around citrus groves. The experience of last winter, however,
as indicated above, shows that truck crops should be planted







Bulletin 174, Controlling the Citrus Aphis


adjoining rather than among the trees, as the cultivation and
fertilizer given the truck crops is apt to keep the trees growing
all winter and so carry over the infestation. If truck crops can
be moved to a point adjoining the grove where they will not
interfere with the program of keeping the trees dormant, much
the same results can be obtained as if they were grown among
the trees.
LIFE HISTORY
Aphis spiraecola has five stages and four molting periods.
The average length of the different stages varies from 20 to 64
hours. The first three nymphal stages are approximately of
equal length, and vary with the season as shown in the following
table (column 1). The fourth nymphal stage is longer (column
2).
(1) (2)
May to August ................................ 20 36 hours
Septem ber ........................... ............... 24 38
October .................-........................ 23 44
November ................................. ... 25 46
December .......................................... 31 64
January ...---..... .... ............................ 29 59*

It is thus seen that during late spring and summer the total
average length of the nymphal life from birth to maturity was
four days, and in December six and a half days. As the mature
female may begin to breed at once the periods represent an
average generation.
In the adult winged female the eyes are carmen; the body
is rather long and plump; head dark; antennae shorter than
body, reaching approximately the fourth or fifth abdominal seg-
ment; body dark green with dark irregular area covering most
of the dorsal part of the thorax. Cornicles, or honey tubes,
slender, tapering slightly at the apex and reaching almost to the
end of the cauda, or tail.
The life of the females used to date in the experiments
ranged from 3 to 47 days. The reproductive period varied from
2 to 24 days. The maximum number of young produced by a
single female to date is 64 and the minimum is 8. The birth
rate was highest in the early life of the female and the most
young were produced in the morning hours. The percentage of
winged individuals produced during the experiments conducted
ranged from 45 to 69.
*January was warmer than December.







Florida Agricultural Experiment Station


Until late in the fall no males were observed, the females
breeding parthenogenetically (that is, without fertilization)
and bringing forth living young. This type of reproduction
also continued all winter but as cold weather came on about De-
cember 1, some males were produced and eggs laid on some
plants as stated above, but not on citrus.

RELATION OF ANTS TO THE APHIS

There is quite a close relation between ants and this aphis.
Three species of ants frequent trees where the aphids are colo-
nized. So constant is this association of ants with aphids that
the presence of numerous ants in a tree is a good indication of
the presence of aphids. The most abundant of the species of
ants is Campanotus sp.
The aphis secretes a sweet fluid known as honey dew which
collects to a considerable extent on the leaves, and this sub-
stance is very attractive to the ants, which feed on it and keep
the foliage clean, thus keeping conditions most favorable for
the feeding and moving about of the aphids. Where there were
no ants it was found that many of the nymphs in moving about
during feeding became entangled in the honey dew which
caused the weak individuals to perish. Therefore, the ant was
found to be a factor in control to a slight degree.
The ants function as the sanitary department of the aphid
colony and do not, as many growers think, feed upon the aphids.




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