Control of the citrophilus mealybug

Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

FIRM.

UNITED STATES DEPARTMENT OF AGRICULTURE

BULLETIN No. 1040

Contribution from the Bureau of Entomology
L. O. HOWARD, Chief

Washington, D. C. PROFESSIONAL PAPER April 12, 1922

CONTROL OF THE CITROPHILUS MEALYBUG.:

By R. S. Woetum,’ Entomologist, and A. D. Borpen,® Assistant Entomologist,
Fruit Insect Investigations.

—_—

CONTENTS.

Page. Page.
Introduction ==> --=-=~-==~=------- 1 | Relation to Argentine ant -________ 8
History and distribution__________ 2 | Comprehensive demonstrations of
Heonomic—importance.— 25 2 = 3 COMER O miss Sea pee A an ee 8
ERO Shap) anit Gee eek Ae Natal cen eli es a0 esate eee 9
Description and life history_______ Ail Sima rin enya ee cee ees 20
Seasonal Mi Stonys == ee 6

INTRODUCTION.

In the fall of 1913 a mealybug infestation was noted on citrus at
Upland, Calif., over an area of approximately 3 acres. At first it
was assumed to be the common mealybug (Pseudococcus citri Risso),
a species highly damaging in some citrus localities but never before
reported in the Upland district. Growers were considerably alarmed
over the discovery, knowing the severity of this pest and the inef-
fectiveness of control in other localities. Considerable damage was
done to the infested groves in a hasty attempt at eradication by
fumigation. At a convention held at Ontario, Calif., on January
30, 1914, the seriousness of the problem was discussed, although no
real solution was evolved. A specific determination was made at
this time by Essig* as Baker’s mealybug (Pseudococcus maritimus
Ehrh.), a species then considered as of minor importance to citrus.
In September, 1915, Clausen,® after a brief investigation of the insect,

1 Pseudococcus gahani Green; order Hemiptera, suborder Homoptera, family Coccide.

2 Resigned September 11, 1920.

3 Resigned December 5, 1921.

4Essieé, E. O.. THE MEALY BUGS OF CALIFORNIA. In Calif. Mo. Bul., v. 3, no. 3,
p. 110-111. 1914.

®> CLAUSEN, CurTIS P. MEALY BUGS OF CITRUS TREES. Univ. of Calif., Bul. 258, p.

30-35. 1915.

2 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

considered it a new species and gave it the name P. citrophilus.

During the first four years various measures of control were tried |

by ne growers and county and State officials without any marked
success; in fact, the infested area continued to increase rapidly and
the infestations became more severe.

The importance of this pest to the citrus industry and inability to
control it led, in-the summer of 1917, to a request for the United
States Department of Agriculture to take up the problem, and the
investigation was immediately started. Effective control methods
were worked out in 1917 and 1918 and were generally employed
throughout the infested area during 1919.

SANTA BARBARA
SAN BERNARDINO

LOS ANGELES

Pasadena
“e Alhambra] @

Upland
® Cucamonga

e Riverside

RIVERSIDE

SAN DIEGO

Fic. 1.—Present known distribution of the citrophilus mealybug (Pseuwdococcus gahani)
in Southern California.

HISTORY AND DISTRIBUTION.

Definite records of the introduction of this mealybug into South-
ern California are lacking, but a study of its earliest occurrence and
spread would indicate that it was brought in on some ornamental
plants imported into Upland during 1910. The infestation of about
3 acres at the time of the first records (1913) had spread by the fall
of 1915 to twice that area. By 1917 approximately 600 acres were
infested, but since that time its spread has been greatly retarded by
control means, though a few small infestations outside of the control
area have been noted (fig. 1).

Shortly after the discovery of the Upland infestation the pest was

found in Pasadena and has now become distributed over a consider-_

3
;

: CONTROL OF THE CITROPHILUS MEALYBUG. 3

able area in the northern part of the city. In 1916 over 100 acres of
citrus were found to be infested at Riverside, and at the present time
this infestation covers approximately 250 acres. Smaller infestations
are recorded at Cucamonga and Alhambra on citrus. It is reported
at Long Beach and Los Angeles on ornamentals and occurs in the
northern part of the State in the San Francisco Bay region.

_ There is little probability of distribution by natural travel as the
insect remains close to its host. The more important means of dis-
tribution are the picking boxes, picking sacks, clothing of the pickers
and pruners, teams, wagons, and ladders; of slightly less importance
is distribution by wind, birds, and insects. Several new infestations
have been definitely traced to distribution through picking boxes pre-
viously used to transport infested fruit.

ECONOMIC IMPORTANCE.

In a severe infestation the mealybug not only masses on the twigs
and foliage but also on the fruit. These masses may even cover from
one-half to two-thirds of the surface and hang down in cottony fes-

| toons from the bud end. Such masses are common on severely in-
| fested lemons and on navel oranges, in the case of the latter particu-
larly at the navel end. Where two fruits touch, a similar favored area
of infestation is formed, especially on grapefruit and lemons. On
| young green fruit the immature forms crowd under the sepals, weak-
| ening the supporting tissues and influencing premature drop. The
~~ insects are also found in numbers on the young succulent new growth
and sucker growth.
; They secrete a honeydew which falls to the foliage or fruit below
) and in this medium grows a black fungus commonly known as
“smut.” The fruit and foliage become so black with this deposit as
ereatly to retard their development and to necessitate a special wash-
ing before the fruit can be packed.
The combination of the attack of the insects uncer the sepals and
the deposit of “smut” frequently causes a heavy dropping of young,
green fruit and also of the mature fruit, if held long on the trees.
| The deposit on the foliage results in a heavy leaf drop, often an
almost complete defoliation of the tree. The feeding of the insects
on the fruit destroys its natural gloss and often causes deep brown
pittings in the rind which seriously affect the grading of the truit.

) One packing-house manager reported a lowering of the grades from
one severely infested orchard of from 30 to 40 per cent of the highest
classed fruit. The lower grades are also seriously affected and fre-
quently fall to culls, or unmarketable fruit. Severe infestations on
lemons have been known to result in an almost complete loss of the
crop, the fruit grading as culls.

4 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.
HOST PLANTS.

The citrophilus mealybug is of importance commercially prin-
cipally because of its infestation of citrus plants. The insect does
occur, however, on a large number of other plants, principally orna-
mentals, upward of
30 different species
being listed as hosts.
On the citrus fruits
it possibly shows its
most rapid develop-
ment on lemons, fol-
lowered by grape-
fruit, navel oranges,
and Valencia or-
anges, in the order
given. It has been
observed to develcp
very rapidly on the
rhubarb, potato,
erevillea, walnut, grape, and on species of Coleus and Pittosporum.

Fig. 2—The citrophilus mealybug: Immature stages of
the female.

DESCRIPTION AND LIFE HISTORY.

The synonymy of the citrophilus mealybug was first correctly de-
terminated by G. F.
Ferris in August of
1919.° As stated, this
insect was first con-
fused with the com-
mon mealybug and
later, by Essig, with
Baker’s mealybug.
Clausen, in Septem-
ber, 1915. noted cer-
tain differences in
him to describe it as
characters which led
a new species (P. cit-
rophilus) but Ferris

found that the same F'!6. 3.—The citrophilus mealybug: Mature stages of the
female.

insect had been de-
scribed by Mr. E. E. Green during May, 1915, as P. gahani from
specimens taken from Azbes sanguinea in London, England. Un-

6 FERRIS, G. F. OBSERVATIONS ON SOME MEALY-BUGS (HEMIPTERA; COCCIDAD). In
Jour. Econ. Ent., v. 12, no. 4, p. 292—293. 1919.

CONTROL OF THE CITROPHILUS MEALYBUG. 5)

fortunately the scientific name cetrophilus had been adopted as the
common name long before the correct determination was given.

The eggs are deposited in a flocculent mass behind the adult female
and may number up to 1,000, though from 500 to 600 is the average.
The period of incubation during the warm season is from 7 to 10 days.

Except in size, the larve are similar to the adult in appearance
after the first molt and pass through three molts before reaching
maturity. The characteristic arrangement of the wax is not strik-
ingly noticeable until after the third molt. The immature stages of
the female are illustrated in figure 2, the mature stages in figure 3.

The following description of the adult of Pseudococcus gahani is

by Mr. E. E. Green: 7

Adult female thickly coated with greyish-white mealy secretion, which is
thinner in the folds of the segments and in the depressed areas. These de-
pressions are in four more or less confluent longitudinal series which are more
marked on the posterior half of the body. The darker color of the insect show-
ing through the mealy covering at these spots, produces a distinct symmetrical
pattern. There is a complete marginal series of 33 short conical waxy processes,
an anterior and posterior pair being usually larger than the others. On each
side of the anal orifice is a much longer, broadly laminate process which is
transversely curved and spirally twisted, and between these is a pair of
shorter processes, which together form a tube. Antenna, 8-jointed, the 8th
longest; first joint strongly developed, approximately as long as it is broad;
antennal formula (excluding Ist), 8 (3,2), (5,4,6,7), the last four being
only approximately equal and varying slightly in their relative positions in

the series. Limbs well developed; tarsus approximately half the length of the

tibiae. Eyes prominent. Mentum distinctly biarticulate; longer than broad;
terminal jo:nt longest, acutely pointed. Dorsal glandular pits present but rather
inconspicuous. Anal ring large and conspicuous, with six long stout setae.
Anal lobes broadly rounded; only slightly prominent; more strongly chiti-
nized than the surrounding parts, the margins of the chitinous area sharply
defined ; each with two stout conical spines, several fine hairs, some conspicuous
circular pores, and a terminal seta which -is approximately equal in length to
those of the anal ring. Margins of segments, each with a small protuberance,
bearing similar spines, pores and hairs, all of which become smaller and less
conspicuous as they approach the anterior extremity. Derm with scattered,
small, and inconspicuous pores. Many longish hairs on under-surface of head.
Length, 2.50 to3 mm. Breadth, 1.25 to 1.50 mm.

Adult male similar in appearance to that of Ps. citri. Length, 1.50 mm.

Though the structural characters agree somewhat closely with those of citri,
the general appearance of the living insect is strikingly different, and it is of
a much more active habit. * * *

Mr. Gahan observes that the insect, when irritated, exudes “a claret col-
oured liquid in round drops, two close to the head end and two at the tail end.’ -
Fhe exudation evidently emanates from the glandular pits that are present in
the positions indicated. He further remarks that the ‘ dark-coloured secre-
tion soon dries, looking like a small balloon. The liquid hardens into a solid
substance which resembles lace or something of a similar nature.”

7 GREEN, E. E. OBSERVATIONS ON BRITISH COCCIDAE IN 1914, WITH DESCRIPTIONS OF NEW
sprcigs. Jn Ent. Mo. Mag., v. 51, p. 179-180. 1915.

6 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

SEASONAL HISTORY.

A most important feature in the biology of this insect was deter-
mined by observing the habits of the insect during the spring migra-
tion. The females, which during the winter have developed almost
to maturity on the twigs, foliage, and fruit, migrate, in the spring,
down the limbs to the trunk to oviposit. This migration usually
begins during the early part of April and continues throughout the
month of May. It is estimated that over 90 per cent of the insects
take part in this movement, although not all have reached full de-
velopment at this time. They settle on the rough places in the bark
of the main limbs and trunk and soon begin ovipositing. On severely
infested trees these accumulations of females with their cottony egg
masses appear as large bunches of cotton hanging from the lmbs
and massed about the trunk and may be collected by handfuls.
(Fig. 4.) These egg masses begin to hatch the latter part of May or
early part of June, and the young larve start a migration back up
the main limbs to the foliage and green fruit. The young settle
along the midribs of young foliage, on the tenderest twigs, and under
the sepals of the green fruit. Here they start feeding and their de-
velopment is comparatively slow. By late fall many have become
half grown and have settled in the more secure positions on the
bud end or navel end of the fruit or between the fruit in clusters, and
their development from then on is very irregular. During the
winter many may have reached the oviposition stage, but the major-
ity of the insects are still immature. There is a great reduction of
numbers throughout the late fall and winter; in fact, on many trees
it is often difficult to find them, but with the opening of spring the
matured forms again enter into the migration. There is only one
main generation a year, although the retarded development of some
insects and the hastened development of others cause an overlapping
of generations and consequently the presence of some insects mm
various stages of development at different times of the year. There
is a possibility of an offhatch or overlapping of generations in the
appearance of egg masses during the winter. This occurrence, how-
ever, is of minor importance in that the numbers of the mealybug are
at their lowest at this time and most of the damage to the host has
already occurred.

The young larve hatching from the egg masses in June are often
Iilled by hot weather. In the summer of 1917 a very large percent-
age of the larvee and eggs were destroyed by a short period of hot
weather when the temperature exceeded 110° F. Again in the sum-
mer of 1918 the hatching occurred just before a warm spell and many
larve were killed. That weather conditions and natural enemies
are powerful factors in the control of this mealybug is very evident,

ww Ss Bat A

oe.

CONTROL OF THE CITROPHILUS MEALYBUG. |

for only a small percentage of the larve hatching from. the egg
masses ever reach maturity. Many are washed off and destroyed by

Fic. 4.—Trunk of lemon tree showing masses of ovipositing females of the citrophilus
mealybug following the spring migration.

rain during the winter months and the development of others is
greatly retarded during this cooler period.

8 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE. ~
RELATION TO ARGENTINE ANT.

In not a single instance has this mealybug become serious except-
ing where it has been attended by the Argentine ant (Jridomyrmex
humilis Mayr). One case was noted in 1918 at Cucamonga where
the mealybug had been observed for several years previous to that
time, but never considered as doing any commercial damage. During
the year 1918-19 the area became infested with Argentine ants and
in the summer of 1919 control work on the mealybugs and ants
became imperative. In every known locality where this mealybug
now occurs it is attended by this particular ant.

COMPREHENSIVE DEMONSTRATIONS OF CONTROL.
EXPERIMENT NO. 1. DEMONSTRATION PLOT.

The orchard selected for demonstration of control methods at
Upland in the summer of 1917 was near the center of the mealybug
infestation (fig. 5) and was considered one of the worst infested
groves, both as regards mealybugs and ants, in the colony. It con-
sisted of two distinct plots of 10 acres each. The first 10 acres were
planted to Valencia (6 acres) and navel (4 acres) oranges and had
in all 674 trees. The second plot was planted largely to navel oranges
(S$ acres), with approximately 2 acres of old lemons, making a total
of 676 trees. The trees were large and the lower limbs rested on the
ground. A careful inspection of the Valencia fruit in August, 1917,
showed an average of over 50 per cent of the fruit on each tree
infested, with from 20 to 35 mealybugs to a fruit, besides the infesta-
tions on the foliage and sucker growth. Many of the trees carried
from 90 to 100 per cent of infested fruit, with the foliage and new
growth as severely infested. Practically every tree had a trail of
ants and many were attended by two and even three trails. The
infestation on navel oranges and lemons in the second 10-acre plot
was as severe but showed only on the small green fruit and new
growth.

ARGENTINE ANT ERADICATION.

Investigations, by the senior writer, of the common mealybug of
citrus trees resulted in the discovery that this insect was effectively
controlled by natural enemies, principally predators, in Argentine
ant-infested territory provided the ants were eliminated. Therefore,
when a survey showed that the citrophilus mealybug occurred exclu-
sively in districts frequented by these ants, the first efforts were con-
fined to a campaign against the ant in the hope that only such activity
would be necessary, as had proved the case for the common mealybug.

CONTROL OF THE CITROPHILUS MEALYBUG.

9

The first operation undertaken was the trimming up of the

branches from the
ground so as_ to
force the ants to as-
cend the _ trunks
where the poison
was placed. Two
men trimming aver-
aged 78 trees per day
of 8 hours at a cost
of approximately 8
cents per tree. The
orchard was in a
state of clean culti-
vation and entirely
free of weeds be-
neath the trees.

Ant control was
begun on about 1
acre of the first 10in
September, and the
remainder complet-
ed by October 5,
1917. The second 10
was covered by ant
control in Novem-
ber, 1917. An ar-
senical-sweetened
sirup, known as the
Barber formula, was
used for the first
distribution in this
orchard, a small
amount being placed
in each container,
one of which was at-
tached to each tree.
(Fig. 6.) Complete
eradication was ef-
fected the following
spring at a cost of
2.6 cents per tree on
the first 10 acres and
at a cost of 4.9 cents

Z
Li

LZ

Fic. 5.—Citrophilus m
=

\

SAWS

y

N

NAAN

NN

LL Ga

mee

#] NN

ealybug control areas, Upland dis-

trict, 1917-1919.

per tree on the second 10 acres. The control is summarized in Table 1.

T8472— 22 2,

10 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

Fic. 6.—Tree trunk showing burlap band and ant poisoned-sirup can in position.

CONTROL OF THE CITROPHILUS MEALYBUG. 10

TABLE 1.—Control of the Argentine ant in a citrus orchard at Upland, Colifz 191%.

DEMONSTRATION PLOT, FIRST 10 ACRES, 674 TREES.

Trees with ants. Check area.
Date of | Poison = x
Bee acipcied ey | M |
ion. tributed. le Weny: |= | e- i | Me-
Clean. | light | tient | dium Heavy Clean. | Very | Light. | dium. | Heavy.
trail. T -| trail. us | light
| | | | | |
| }
Sephies 4 oe or - 5 | 993) BIO ts irs cae iceman Teese atecl| a een CS) he mec
Oct -5 OW ereMiReran Cae rerea etd sete eee eS io Ee OS ee |e ene
Mari DAs cei Sat oe (37/2 [eee Sie | aaa eee aes | eens [ieee i Berea stapes ener | ree ae
Apr. 9 Only on trees with ants. ~—|........ ooeecae |recoereeiere Wai] son ladda | orate Shea
AcpEnO eens | sacs one: 648 | 20 Goleta te See ie a Sees ee el eae ie aan A Ione Pe be
June 17 Only on trees with ants.
JUM GH esa ee ce 642 | 17 TH as Seed gue Bea oe 3 eae Ca Oo | Teepe | Fa eek
EMOI29 See ete ees 672 Pal aaa ass a |b Scless Soe | gi ae rg [Piaaatiete tt vrall gcse fs teal Jes 2 Pas leyee seas
DEMONSTRATION PLOT, SECOND 10 ACRES, 676 TREES.
| | | |
NODbs23z4 lace wee 2 157 | 266 | 107 | 68a = | 9 | 23 | 20 | 24
Nov. 5 | On 600 trees. Trap nest under 76 trees.
Mare 205s 4|cee ce. | 391 | 119 | 61 | 15 | 14 Sales eee | 19 | 23 | 26
ANS OV 17 Gas GO OKERCES sae toe tires Nees ei on Ea rape eS a (eee ceee We Ce
ANY Oy isles G5 a fesse © a A an ee aan ae re | NG oy On 76 trees.
Apr 0s le | 546 39 10 4 1 | 57 13 5 | 1 0
UMMC BNE |e ee re 577 18 5 0 0 | 75 1 0 | 0 0
JUNE ORS lees ee 593 7 0 0 0 76 0 0 0 0
| |

BuRLAP BANDING.

Although by winter the ants were controlled and early the follow-
ing spring were almost completely eradicated, the mealybugs con-
tinued in severe infestations and during the latter part of March were
noted to begin descending the tree trunks. The descent continued to
increase in April and no large number of natural enemies appeared
as Was anticipated. It soon appeared that elimination of the ant was
not alone sufficient to bring about control of the citrophilus mealy-
bug, as had proved the case for the common mealybug. The citro-
philus mealybug species was not attacked by either numerous or
effective natural enemies. The necessity of artificial means of con-
trol to supplement ant eradication was thus at once apparent.

A study of the habits of this mealybug showed a spring migration
to the trunk and rough places on the main branches where egg
masses for the succeeding generation are deposited. The accumula-
tion of insects and egg masses in cases of severe infestations, as pre-
viously pointed out, became so great as frequently to present the ap-
pearance of large tufts of cotton. This massing on the trunk and
lower branches presented a favorable point of attack and the spray-
ing of these masses with an effective insecticide promised a great re-
duction of the total insects present. It was noted, in the case of
some trees which had been banded with cotton bands by an orchardist
at Upland in 1915, that these acted to attract the ovipositing females
beneath them in great masses. Since cotton bands were scattered
by the winds and birds, it was decided to substitute burlap and ac-

19 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

5s cighied ey

EE Oe aoe ee

4
*

Fie. 7.—Trunk of lemon tree with burlap band removed showing masses of ovipositing :
females of the citrophilus mealybug collected under band.

cordingly in the spring of 1918 the trees in the demonstration orchard
were thus banded. (Fig. 6.) A band of burlap about 6 inches wide
was wound around the trunk just below the main branches and )
caught at each end with a finishing nail. The migrating females

= Tr.” =

=

CONTROL OF THE CITROPHILUS MEALYBUG. 13

readily collected under the bands preparatory to oviposition.
(Fig-7.) |

The success of burlap bands as used on the demonstration plot led
the growers throughout the infested area to adopt the practice. This
necessitated a large supply of burlap bands and the problem was
solved by buying the burlap of 30-inch width in bolts of about 100

yards. The bolts were cut at a printing office undera large paper

knife into six rolls, 5 inches in width, which could readily be carried
into the orchard and cut in appropriate lengths for individual trees.
The ends of each band were fastened over a 4d finishing nail driven
into the trunk of the tree. The average orchard of 900 trees was
banded with one full bolt of burlap. The average cost in 1919 was
as follows:

i ror purtap: lOO yards) = = Se Peper iea sty ta oe SADE GG
Gating 22s es Sao So Sas S ee SS 1. 00
Ioan iGen Ss Sere ee Se eee Se ae 15
Linpes Sie) Goal VERS 0036 Chases C56 3 ee Rabe eRe es Sea pea es ge eee 3. 00

16. 75

Cost per tree, approximately $0.02.

During April and May insects continued to descend in great
numbers, the burlap bands proving a center of attraction. In cases
of light infestation the majority of the descending insects would set-
tle beneath the band, and this was particularly true on smooth-

barked orange trees. (Fig. 8.) Lemon trees with the more irregu-

lar trunks and depressions where the main branches join the trunks
offered favored places for the mealybugs to settle, although even
these seemed less favored by them than the bands. By the latter
part of May hatching started, following which the larve migrated
back to the foliage and fruit on the tree. Before this happened the
bands were removed and dipped in an effective insecticide, usually
pure petroleum distillate, and the trunks were then sprayed.

SPRAYING.

Spraying operations on the first 10 acres were conducted on May
23 and 24, and on June 6 and 7 on the second 10 acres. Only the
main limbs and trunks were sprayed and for this a petroleum dis-
tillate-soap emulsion apphed with a power sprayer at 150 pounds
pressure proved most satisfactory. Two leads of hose with angled
Bordeaux nozzles were used. The burlap bands were removed and
thoroughly sprayed as the trunks were being sprayed. The formula
used was as follows:

Hiscutater s' = [On SOs 5 be ee ee ee See a panes gallons__ 10
SEO ea} ONY Cle ene ee ee Lge ete ee eae en ee pounds__ 20
NRCC TE Ge INAK Cx Secses: Seb a ee gallons__ 200

If a lighter oil, as stove distillate, is used, the amount should be increased to
15 gallons. A good agitator is necessary in mixing the spray. After a few

14 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

inches of water are in the bottom of the tank, the soap powder is sifted in
as the tank is beng filled and the agitator is running. The oil is added last
before the tank is full.

“
:
4
i
-
4

Fic. 8.—Three burlap bands from the trunks of orange trees following spring migration x.
of the citrophilus mealybug.

It was felt that the spraying of the bands was not entirely satis- .

factory unless the greatest care was used, so in subsequent work it

« . ¢

was decided to dip them just before spraying. The application, to

“CONTROL OF THE CITROPHILUS MEALYBUG. 15

be effective, must be thorough and to accomplish this it is necessary
to go beneath the tree. The most satisfactory work was done when
the nozzle was connected directly to the hose, allowing free manipu-
lation in any direction. A long rod should never be used as it does
not allow the ready manipulation necessary on heavily branched
trees to spray from any direction.

The trees on the demonstration plot were of an open type with
smooth trunks and high headed, so they could be entered with ease
and quickly and thoroughly covered with spray. It required only
34 tanks of spray to cover each of the 10 acres. The cost (1918) is
summarized herewith:

Socallons-distilates at $0.05 per gallon === se E
70 pounds. soap powder, at $0.05 per pound... >. 3. 50
WenmeangsteaMister-tOr 14 Gays = tS ee 9700
Two men spraying for 14 days_ apes: s ee whe eho a OO
Gasolme-and oil-- = == Ss ee for le AWE IE a ee)

Re fal S25 = rycen oe state OEMS Sy SO ss 24.50

Cost per tree, $0.036.

The time, 14 days, included considerable engine trouble. Fifty-
two trees were sprayed in 30 minutes. A tank of spray (200 gallons)
covered approximately 200 trees.

Several days after the spraying the burlap bands, now dry, were
replaced on the tree trunks and left for a year. At no time were
insects noted under the bands except an occasional one, which the
natural enemies destroyed before oviposition was completed.

Throughout the following fall and winter (1918-19) it was very
difficult to find even individual mealybugs, and the packing house
handling the fruit reported it to be cleaner than any that had been
turned in during the five preceding years, with an increase of grade
amounting to from 30 to 40 per cent.

During the spring of 1919 an inspection was made of the demon-
stration plot and very few mealybugs and no ants were found.
Under the old bands not more than 10 to 12 insects were found on
any one tree. The grove was sprayed again by the owner in June
of 1919, as outlined above. An inspection in May, 1920, showed a
practically clean grove, not more than 5 insects being found under
the bands of any tree, and most of the trees were entirely free of
mealybugs.

EXPERIMENT NO. 2. FARLOW GROVE, 888 TREES.
In the summer of 1919 a second demonstration plot was employed

which consisted of 10 acres of heavily infested oranges. Ant control
and banding had been carried on the previous spring, and the ants

were greatly reduced at the time of spraying. In this grove, as in

the former, a power sprayer with two leads of hose and Bordeaux

16 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

nozzles were used. Distillate-soap powder emulsion, soap powder,
and water were used, as shown in Table 2, and data were see
on the efficiency of the different solutions.

Before the spraying started a man was sent through to remove
the heavily infested bands, dip them in pure distillate, wring them
out, and place them to one side to dry.

TABLE 2.—Summary of spray operations against the citrophilus mealybug.

Average |
Average | Average =
EOL number spray nee Effective-
Spray. * | oftrees | time ness of
of trees per |soper gallons spray
sprayed. : az per
tank. | tank. te
| Min.
5 per cent distillate-soap powder emulsion......... 777 59 | 58 | 3.4 Excellent
SW ied Ore Se Ow sea wie Era te ae ne 69 34 | 85 5.7 | Poor.
40 pounds soap to 200 gallons water..........-..-- 42 42 45 | 4.8 Do.

Both the water and soap-powder treatments were discontinued, as
it was found to be impractical in application to get a thorough clean-
up of the egg masses. The distillate-soap emulsion was quicker in
application and more effective.

The bands were replaced shortly after the completion of the spray
work, and field observations made from time to time throughout the
following year. Though some mealybugs appeared under the bands
ieniae the spraying, they were completely controlled by natural
enemies anf required no further treatment. Throughout the fall and
winter no mealybugs were apparent, and in the spring of 1920 so few
mealybugs appeared under the bands that hand treatment was all that
was required. The grove is now commercially clean, and there has
been a marked increase in the grade of the fruit.

The data obtained in this experiment not only demonstrated the
practicability and efficiency of the distillate-soap emulsion but also
demonstrated the advisability of proper pruning before spraying.
The trees on this grove were low on the ground and it was difficult
to treat the trunks owing to low branching and inside growth. In
consequence of this condition it took much more material and a longer
time to make the application. The cost of spraying was as follows:

Removing and dipping bands, 1 man, 1 day_1_____________- $3. 00
164 tanks spray:
330 pounds soap powder, at $0.07 per pound____________ 23.10
165 gallons distillate, at $0.07 per gallon______________ 11. 55
Two men: at $4 per day, 2 days-2 244 ee ee eee eS ia B43 ¢3 16. 00
Feam;-at $4 per. day; 2. days22: . eee ee ae 8. 00
Gasoline.and pil, -2 Ga ysecc ao a ee eee 2 50
Wotalss. fo 6 2 sled Te Bat BS See ee ee eee eee 64.15

Cost of $0.072 per tree.

CONTROL OF THE CITROPHILUS MEALYBUG. 17

HAND-TREATMENT METHOD.

In a 5-acre citrus orchard, comparatively lightly infested with
mealybugs and banded early in the spring of 1919, the hand-treat-
ment method was effectively employed. This consisted of removing
the bands and dipping them in a bucket of 25 per cent distillate-
soap emulsion, wringing the bands out dry, scrubbing the trunks with
a suitable brush, and replacing the bands.

Different strengths of the emulsion were tried with results as
shown in Table 3.

TABLE 3.—Results of hand-treatment method against the citrophilus mealybug.

Effectiveness—

Strength of solution.

| On adults. On egg masses.
BERCISCOH teeter ae ees eee ee Pee a Poomkitlin pees 45 5 ees | No effect.
LOS CTIGEM ies eae Sse ee Se ee ee | 50 per cent killing........_.. | Poor.
DERE: COM Geese es er ee Re 100 per cent killing..........| Excellent.

The 25 per cent solution is prepared as follows:

Place 6 quarts of water in a bucket and thoroughly dissolve 4 pound of soap
powder. To this slowly add 2 quarts (30° Baumé) distillate while constantly
stirring. Attach the bucket pump and pump the solution back into the bucket
through a mist nozzle until a perfect emulsion, free of oil globules, is obtained.
The emulsion should be used soon after preparation.

Fic. 9.— Adult of Chrysopa californica. Much enlarged.

Several growers have used this method successfully on hght in-
festations, where followed up at intervals of about every two weeks
from the middle of May to the latter part of June, at a cost of 2 cents
per tree for each treatment. It is as important to effect ant eradi-
cation when this method is employed as it is with the regular trunk-
spray method.

- CONTROL WORK—UPLAND DISTRICT, 1919.

The great success of the demonstration work of 1917 and 1918 led
to the general adoption of the control methods by the growers
throughout the infested area. (Fig. 5.) Up to and including 1919
ant control was practiced on 630 acres. The entire mealybug-infested

18 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

acreage was banded with burlap in the spring of 1919. Of the area 7

infested with the mealybug in that section all but 10 acres were
sprayed according to the methods outlined, with excellent results
throughout. The 10-acre orchard was left as a check for control by
natural enemies.

The ant control was handled partly by the growers themselves,
partly by the citrus associations of which the orchardists were mem-
bers, and partly by
contract operators.
The sirup was for the
most part prepared
by the citrus associ-
ations, or purchased
from druggists at a
cost of $1.50 to $2 a
gallon. The spice
tin was the _ pre-
ferred container.
The average cost to
the grower for ant
control, including
refilling where nec-
essary, was 4 to 6
cents per tree. The

cost of burlap band-
Fig. 10.—Adult of Leucopis bella. Greatly enlarged. ing averaged 2 cents

per tree. The cost of trunk spraying varied. On dense, unpruned
lemon trees, headed low, spraying proved somewhat difficult and
slow. The amount of material used on such trees was also greatest.
High-headed orange trees with smooth trunks were most easily
and effectively sprayed.

These spray operations were conducted by the growers and com-
mercial outfits and an average of 10 acres a day was covered at a cost
approximating the figures given for the two demonstration plots, the
cost being more or less proportional to whether the trees were well
pruned and open or unpruned and difficult to spray. Work carried
out by the owners themselves was for the most part thoroughly done.
A few orchards were trunk-treated by hand.

The general results of the control campaign of 1919 at Upland

were very gratifying. Orchards which had shown severe infesta-
tions in the spring of 1919 were commercially clean in the spring
of 1920. The reduction in grade or total loss of fruit from mealy-
bugs had been reduced to a neglhgible factor. Packing-house man-
agers and growers were convinced that the citrophilus mealybug
was no longer a menace to their orchards and that the control of

x
3
.
.
|

eer

a a

CONTROL OF THE CITROPHILUS MEALYBUG. 19

this insect was'on such an effective commercial basis that timely
future attention would effectively hold it in check.

NATURAL ENEMIES.

Though the ant control, banding, and trunk spraying have given
excelleat contro] of the citrophilus mealybug, the importance of its
natural enemies in conjunction
with this artificial means of con-
trol needs emphasis. The nat-
ural enemies are very effective
against light infestations, if the
ants are not present, and even in
heavier infestations are impor-
tant in assisting to destroy the
insects on the foliage and trunks
following spray treatment. The
most effective natural enemies
present in the groves are all
predators and appear to rank
in order of importance as fol-
lows: Chrysopa spp. (fig. 9),
Leucopis bella Loew (fig. 10), Fue. ar eas te ee sordidus.
and Scymnus sordidus Horn
(fig. 11). They breed freely in the cottony mass of ovipositing fe-
males on the trunks, although by no means noticeably reducing the
mealybug on heavily infested trees. It is,
however, following the migration of the
mealybug larve to the tender fruit and
fohage that the effectiveness of these nat-
ural predators is most felt. Here they
search out and destroy the young mealy-
bugs, and in the case of hight infestations
frequently prevent the development in-
creasing to severe proportions. Chrysopa
and Leucopis are usually most numerous
during the late spring and summer, while
Scymnus is most effective during the early
fall.

The natural predators of primary im-
portance in controlling the common mealy-

Fic. 12—Larva of Cryptolae. bug, namely, Sympherobius spp. and

mus montrouzieri. Much en-

sta ae Hyperaspis lateralis Muls., are of very
arged. 4

secondary value against the citrophilus
mealybug. Cryptolaemus montrouzieri Muls. (figs. 12, 13), however,
is very effective against either species. This predator was first tried
against the citrophilus species by the writers at Alhambra during

20 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE.

1916 and proved so effective that several hundred were distributed

beneath a tented citrus tree at Upland during the autumn of 1917.
Some specimens successfully passed the winter and started breeding
freely the following spring. The Insectary Branch of the California
State Commission of Horticulture followed the writers’ lead and has
since distributed many thousands over the Upland district, with such
successful returns that the work should be supported and continued.

SUMMARY.

(1) Ant control. This is most effectively accomplished by the use
of a special arsenical poisoned sirup in small contamers, one to each
tree. Best results follow dis-
tribution during the autumn or
spring.

(2) Trunk banding. Strips of
burlap about 5 inches wide
should be placed around each
tree trunk, from February to
April, to attract ovipositing fe-
male mealybugs.

(8) Removal and dipping of
burlap bands in distillate. This
should precede the trunk spray-
ing. The bands should be dry
when replaced after the trunk
treatment.

(4) Trunk treatment. Spray
thoroughly with distillate-soap
powder emulsion after the mealybugs have massed on the trunks
and just before the eggs begin to hatch. This is usually during the
latter part of May.

(5) The propagation and distribution of Cryptolaemus montrou-
ziert, Leucopis bella, Chrysopa spp., and Seymnus sordidus are to
be recommended.

Fig. 13.—Adult of Cryptolaemus mon-
trouziert. Much enlarged.

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