 

 TEXAS AGRICULTURAL EXPERIMENT STATION

B. YOUNGBLOOD, DIRECTOR
COLLEGE STATION, BRAZOS COUNTY, TEXAS

l BULLETIN N0. 353 APRIL, 1927

DIVISION OF ENTOMOLOGY

    

 HE INFLUENCE OF PARENTAGE, NUTRI-

TlON, TEMPERATURE, AND CROWDING

 ON WING PRODUCTION IN APHIS’
GOSSYPII, CLOVER

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. O. WALTON, President

L‘ B R A R Y iT Ya‘
‘ ~ '\ a F,’ .
Agmunuyal 3. Merthamcal MM’??? “

(JuHE-ge 5lannn. 9* 

209-22 7- 6000-L1 80'

   
 
   
 

STATIQN STAFFT

ADMINISTRATION‘ - PLANT PATHOLOGY AND PHYSIOLOGY: i
 gfjtélégzlézqoMlf/Istsgsgig%irgafsctor J. J. TAUBENHAUS, Ph. D., Chief I
R. E. KARPER, B. S., Acting Vice-Director FARM AND RANCH ECQNQMICS;
J. M. SCHAEDEL, Secretary_ I_,_ P_ GABBARD, , e i
M. P. HOLLEMAN, JR» Chief Clef/f *B. YOUNGBLOOD, M. S., Ph. D., Farm and
J. K. FRANCKLOW, Assistant Lhief Cler/-: Ranch Economist
CHESTER H1605, Elecllilve Asslﬂam G. L. CRAWFORD, M. S., Marketing Research
C. B. NEBLETTE, Technical Assistant V LSplecialisltvl S G _ R h B _
VETERINARY SCIENCE; . . ORY, . ., razing esearc otanist
=|<=|=M_ FRANCIS, D. V. M., Chief ***T.  GAsromdJilxi, B. S., Assistant. Farm
_v_ q V; ' ' ecor s an ccoun s
 11)). V.   ***J- IEII-ngetxﬁéoghtﬁ. Assistant. Ranch Record: _
CIh§1§iI1§§§e§fPh.o., Chief; State Chemist SOIL svRvEY= _
S. E. AsBUnY, M. S., Assistant Chem_ist **’}"{WWT-I$ARTER,  S-SC/Ilef
WALDO H. WALKER, Assistant Chemist - - AWKER, 011 “We!!!”
VELMA GRAHAM, Assistant Chemist E. H. TEMPLIN, B. S., Soil Surveyor
Amm E. STURGIS, B. S., Assistant Chemist T- C- REITGH. B- 5» $011 Surveyor
g.  (éARLYLlLﬁ. S., gssisttantt ggemistt BOTANY:
. . ROOKE, . ., ssis an €_lTllS -
T. L. OGIER, B. S._, Assistant _Chemist H" NESS’ M‘ S" Chlef
J. G. EvANs, Assistant Chemist PUBLICATIONS: _
HORTICULTURE: A. D. JACKSON, chlef
W. B. LANHAM, M. A., Chief .
H. NEss, M. s., Berry Breeder Svgfgf PIfIAIIIEPIQIIIIS)_IfE;M-Ef

RANGE ANIMAL HUSBANDRY:
J. M. JoNEs, A. M., Chief; Sheep and Goat DAIRY HUSBANDRY:

Investigations _ -———————---—-, Chief

J. L. Lusn, Ph. D., Animal Husbandman;

Breeding Investigations - POULTRY HUSBANDRY‘

W. H. DAMERON, B. S., Wool Grader R~ M- SHERWOOD- M- 5-» Chief
ENTOMOLOGY: _ RURAL HOME RESEARCH:
F. L. THOMAS, Ph- D» Chlff; $1016 JESSIE WHITACRE, Ph. D., Chief
Entomologist _ .
H. J. REINHARD, B. S., Entomologist ****AGRICULTURAL ENGINEERING:

W. L. OWEN, JR., M. S., Entomologist
S. E. McGnEGoR, Jn., Acting Chief Foulbrood MAIN STATION FARM;
Inspector I G. T. McNEss, Superintendent

, F lb dI t \
B???SMTZZZZZENYieliiiieefiffeiiie, APICUETHIZA? BI§SEARCH LABORATORY
an ll 0nl0

       
    

AGRONOMY‘ . H. B. PARKS, B. S., Apiculturist in Charge
  I}:EOyl?1\(I)lI3‘ll\),S’1\1/Y.LSS:’ ggiiijiiomist, Grain A‘ H’ ALEX’ B‘ s" Queen Breeder
Sorghum Research _ FEED CONTROL SERVICE:
R. E. KARPER, B. S., Agronomist, Small F. D. FULLER, M. S., Chief
Grain Research _ S. D. PEARCE, Secretary
P. C. MANGELSDORF. SC. D., Agronomist; J, H, RQGERS, Feed Inspector
Corn and Small Grain II1U€8il_(](l_ilOIlS W. H. W000, Feed Inspector
D. T. KILLOUGH, M. S., Agronomist, Cotton K. L. KIRKLAND, B. S., Feed Inspector "
Breeding _ _ W. D. NORTHCUTT, JR., B. S., Feed Inspect
E. C. CUSHING, B. S., Assistant in Crops E. H. GARRETT, Feed Inspector ~
SUBSTATIONS 
No. 1, Beeville, Bee County_: No. l0, Feeding and Breeding Station, ne -.
R. A. HALL, B. S., Superintendent College Station, Brazos County: »
, - R. M. SHERWOOD, M. S., Animal Husband
No. 2, Troup, Smith County: man in Charge of Farm i
W- S- HOTCHKIS5» Superlmendent L. J. MCCALL, Farm Superintendent
No. 3, Angleton, Brazoria County: _ L N .
R. H. STANSEL, M. S., Superintendent N(i_I_1F_ ﬁggiﬂgfﬁﬁlf§§§f,‘}f,1}f,§dg§““"
No. 4, Beaumont, Jetferson County: ***N _ 12 ~||~ t}, , H d C t :
R. H. WYCHE, B. S., Superintendent _]_ 1% QI’JI?,:'Y:%_ S?’ Ssgerel-ﬁggdeytun y
No. 5, Temple, Bell County: ***JosEPn C._ STEPHENS, M. A., Junior
H. E. REA, B. S., Superintendent Agronomlst

No. 14, Sonora, Sutton-Edwards Counties:

No’ 6’ Denum’ Demon County: E. W. THOMAS, B. S., Superintendent

P. B. DUNKLE, B. S.,'Superintendent Wv L‘ BLACK’ D. V_ M‘, Veterinarian '
No, 7, Spur, Dickens County; _ V. L. CORY, M. S., Grazing Research _Botani
R. E. DICKSON, B. S., Superintendent ***0. g-tB-ARCQCR, B- S» Cvllllbvfﬂilﬂtl
n omo ogis
No. 8 Lubbock Lubbock County: ()_ ]_,_ C , 5h h d
D' I“ J°NES',S“P"""""d-‘"'- N 1s wzlzifelliniliidaig: Ciaunty-
FnAblléiurgiégqiil’ Iniﬂatlonlst and Forest (W.  FRIENDZBB SS., Superilntehdent
M. McPHAIL, . ., Entomo ogist
N0~ 9, Bﬂlmﬂfheﬂ, Reeves CPIIMYI No. 16, Iowa Park, Wichita County:
J- J- BAYLES, B- 3» superintendent E. J. WILSON, B. S., Superintendent

Teachers in the School of Agriculture Carrying Cooperative Projects on the Station:

G. W
S. W. BILSING, Ph. D.. Professor of Entomology

G. P. Gnour, M. S., Professor of Dairy Husbandry

V. P. LEE, Ph. D., Professor of Marketing and Finance

. ADRIANCE, M. S., Associate Professorof Horticulture

Professor of Agricultural Engineering

. SCOATES, A. E., _ _
S., Associate Professor of Agricultural Engineering

D
H. P. SMITH, B.

TAs of April 1, 1927.
*On Leave.
**Dean, School of Veterinary Medicine.
***In cooperation with U. S. Department of Agriculture.
****In cooperation with the School of Agriculture.

 

SYNOPSIS

There are two forms of the cotton louse, Aphis gossypii.
One form has fully developed Wings and the other form is
Wingless. This is a technical Bulletin and contains the results
obtained from the studies on the inﬂuence of parentage, nutri-
tion, temperature, and crowding on the production of the
winged forms. It was found that the normal tendency for
this insect is to be Wingless. The production of wings is de-
pendent entirely upon environmental inﬂuences. Starvation
produces an increased number of winged individuals in the
progeny of wingless mothers but has little or no effect in stim-
ulating wing development in the offspring of winged. mothers.
Temperatures ranging from 70° F. to 90° F. do not affect the
proportion of forms produced in this species. When these in-
sects are crowded during development an increased number of
winged forms occur. Crowding was found to be the dominant
if not the controlling factor in stimulating the production of
wings. No correlation was found to exist between the pre-
vailing relative humidity in which the insects were reared and
the ratio of winged to Wingless forms produced.

TABLE OF CONTENTS

 

PAGE »
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 i

Review of Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

The Effect of Parentage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _. 6

Summary of the Effect of Parentage . . . . . . . . . . . . . . . . . . . . . . . 8 _

The Effect of Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1'

Summary of the Effect of Nutrition . . . . . . . . . . . . . . . . . . . . . . . . '10 I

The Effect of Temperature. .< . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . . . 11

Summary of the Effect of Temperature . . . . . . . . : . r . . . . . . . . . . 14 -

The Effect of Crowding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 7

Summary of the Effect of Crowding . . . . . . . . . . . . . . . . . . . . . . . . 18

Observations on the Effect of Humidity . . . . . . . . . . . . . . . . . . . . . . . . . ' 18 r

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19 -

Literature Cited . . . . . . . . . . . . . . . . . . r . . . . . . . . . . . . . . . . . . . . . . . . . 19 _

BULLETIN No. 353 APRIL, 1927

THE INELUENCE OF PARENTAGE, NUTRITION, TEM-
PERATURE, AND CROWDING ON WING PRO-
DUCTION IN APHIS GOSSYPII, GLOVER

H. J. REINHARD

  
  
 
 
 
 
  
 
  
   
   
   
   
   
  
  
 
 
    
   
  
  
  

Incidental to th.e life history studies of Aphis gossyp/ii by Paddock
a (6), some observations on factors affecting dimorphism in this species
I were made. These preliminary observations resulted in a more com-
 plete study of the effect of parentage, nutrition, temperature, and crowd-
f, ing on the ratio of alate to apterous forms produced in this species.
“ The work was begun in March 1924 and continued with interruptions
 until October 1926. The results of these studies are given in this paper.

REVIEW OF LITERATURE

 The inﬂuence of parentage, nutrition, and temperature as factors af-
ffecting the proportion of alate and apterous forms of aphids has been
noted by a number of investigators. The results of experiments con-
o ducted by Ewing (3), Gregory (5), Shull ('7), Wadley (8), and Ewing
.](4), are extremely interesting and signiﬁcant contributions to the sub-
ipject. Ewing (3), working with the apple-grain aphid, then known as
TAphis avenue Fab, found that temperature changes alone were capable of
laﬂiecting dimorphism, and that fewer winged aphids were produced in a
imoderate temperature than in lower or higher temperatures. Gregory
,; (5) found that the green pea-aphid, M icrosiphum destructor J ohn., when
T starved during development produced winged progeny and assigned
nutrition as the primary factor in determining the development of Wings
‘in the offspring of Wingless mothers. Shull ('7), working with Macro-
‘siphuim solcmifolii Ashm., noted that winged aphids produced largely
apterous progeny, and that Wingless individuals produced many alate
Tprogeny, and concluded that parentage was the dominant factor in wing
development. Wadley (8), experimenting with Rhopalosiphum pruni-
Qfoliae Fitch, showed that all three factors, viz, temperature, nutrition,
and parentage, affected the proportion of alate and apterous forms pro-
duced and concluded that deﬁnite relations existed among them in their
5eifect on wing development. Ewing (4) conﬁrms this opinion in the
., ollowing words: A

 “Among the outstanding factors that have been demonstrated ex-
rimentally as affecting the ratio between the two agamic forms of
phids are inheritance, temperature and nutrition, and the relative im-
‘ortanee of each of these appears to depend on the conditions imposed
y the combination of all other factors. Either inheritance, tempera-
é re or nutrition may under certain conditions become the dominant or
r Yen the controlling factor.” .

I This previous work was used as a guide in arranging experiments to

 

6 BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

study the inﬂuence of parentage, nutrition, temperature, and crowding on
wing development in Aphis gossypii Glover, commonly known as the
cotton or melon aphid. The data obtained from these experiments with
certain conclusions are presented in this paper as a contribution to our
present knowledge of this apparently elusive yet popular and interest-
ing subject.
“ THE EFFECT OF PARENTAGE

A study of the inﬂuence of parentage and ancestry on the production
of alate and apterous forms of Aphts gossypivl was begun on October 10,
1925, and continued without interruption for one year. During this
time 59 complete generations were produced in the laboratory and in-
sectary on young succulent cotton plants grown in pots and protected
by street-lamp globes.

Beginning with an isolation of an apterous agamic individual, this
form was selected as the parent of each succeeding generation. The
progeny of each parent was transferred to an uninfested plant and reared
to maturity. Temperature and humidity conditions were recorded by a
hygrothermograph. The data obtained in this experiment are pre-
sented in Table 1.

Table 1.——-Apterous Generation Series

_ Date Number
Generation Date Born Matured Reared .l\pterf_ous Alate
1 . . . . . . . . . . . . . . . . . . . . . .. Oct. 10, 1925 Oct. 19, 1925 9 9 0

2 . . . . . . . . . . . . . . . . . . . . . .. Oct. 20, 1925 Oct. 26, 1925 25 25 O

3 . . . . . . . . . . . . . . . . . . . . . .. Oct. 27, 1925 Nov. 2, 1925 31 31 0

4 . . . . . . . . . . . . . . . . . . . . . .. Nov. 3, 1925 Nov. 8, 1925 21 21 O

5 . . . . . . . . . . . . . . . . . . . . . .. Nov. 9, 1925 Nov. 15, 1925 17 17 0

6 . . . . . . . . . . . . . . . . . . . . . .. Nov. 16, 1925 Nov. 23, 1925 14 14 O

7 . . . . . . . . . . . . . . . . . . . . . .. Nov. 24, 1925 Nov. 30, 1925 17 17 O

8 . . . . . . . . . . . . . . . . . . . . . .. Dec. 1, 1925 Dec. 7, 1925 ll 11 O

9 . . . . . . . . . . . . . . . . . . . . . .. Dec. 7, 1925 Dec. 13, 1925 25 25 O

1O . . . . . . . . . . . . . . . . . . . . . .. Dec. 14, 1925 Dec. 19, 1925 19 19 O

11 . . . . . . . . . . . . . . . . . . . . . .. Dec. 20, 1925 Dec. 27, 1925 19 19 O

12 . . . . . . . . . . . . . . . . . . . . . .. Dec. 28, 1925 Jan. 2, 1926 14 14 0

13 . . . . . . . . . . . . . . . . . . . . . .. Jan. 3, 1926 Jan. 9, 1926- 13 13 0
Jan. 15, 1926 36 32 4
Jan. 22, 1926 l3 13 O
Jan. 28, 1926 31 31 O
Feb. 3, 1926 7 7 0
Feb. 8, 1926 27 27 O
Feb. 14, 1926 81 75 6
Feb. 20, 1926 16 16 O
Feb. 26, 1926 19 19 O
Mar. 3, 1926 19 19 0
Mar. 9, 1926 27 27 O
Mar. 15, 1926 29 22 7
Mar. 21, 1926 17 17 0
Mar. 28, 1926 25 25 0
April 3, 1926 21 21 0
April 9, 1926 9 9 0
April 15, 1926 22 22 O
April 21, 1926 11 11 O
April 26, 1926 1O 1O 0
May 2, 1926 18 18 0

ay 7, 1926 17 17 0

May 12, 1926 17 17 0

May 17, 1926 15 15 0

Nay 22, 1926 12 12 0

May 27, 1926 15 15 0

38 . . . . . . . . . . . . . . . . . . . . . .. May 27, 1926 June 1, 1926 13 13 0

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 7

Table 1.—Aptcrous Generation Series—Continued

_ Date Number
Generation Date Born Matured Reared Apterous Alate
June 2, 1926 June 8, 1926 14 14 O
June 8, 1926 June 13, 1926 13 13 O
June 14, 1926 June 20, 1926 15 15 0
June 20, 1926 June 25, 1926 13 13 0
June 26, 1926 July 1, 1926 14 14 O
July 2, 1926 July 8, 1926 15 15 O
July 9, 1926 July 14, 1926 14 14 0
July 15, 1926 July 20, 1926 13 13 0
July 20, 1926 July 25, 1926 15 15 0
July 26, 1926 July 31, 1926 16 16 0
July 31, 1926 Aug. 5, 1926 17 17 0
Aug. 6, 1926 Aug. 11, 1926 13 13 0
Aug. 12, 1926 Aug. 17, 1926 12 12 0
Aug. 18, 1926 Aug. 25, 192 12 12 0
Aug. 26, 1926 Aug. 31, 1926 14 14 0
Aug. 31, 1926 Sept. 6, 1926 13 13 -O
Sept. 7, 1926 Sept. 14, 1926 16 16 0
Sept. 14, 1926 Sept. 20, 1926 11 11 0
Sept.2l, 1926 Sept.26, 1926 15 15 O
Sept.26, 1926 Oct. 2, 1926 13 13 O
Oct. 2, 1926 Oct. 8,1926 9 9 0

 

The continued selection of the apterous agamic form, it will be noted,
reproduced a like form throughout the entire generation series except
in three instances. In each of these cases the Winged form appeared
evidently in response to another factor, viz., crowding, which uninten-
tionally was permitted to occur for a period of time sufficient to pro-
duce its effect. A more complete discussion of crowding as a factor
affecting wing production will be given elsewhere in this paper.

An attempt was made to run a parallel series of alate generations
under conditions identical with those in the experiment described above.
However, it was found to be impossible to maintain consecutive genera-
tions of the alate agamic form. The progeny of winged mothers in-
variably were Wingless and their offspring continued to reproduce the
ivingless form as long as crowding was not permitted to occur. This ex-
periment was therefore discontinued after the fifth-generation descend-

ants of an alate stem mother had reached maturity. The results of

this experiment are given in Table 2.

Table 2.—-Alate Generation Series

_ ‘ Date Number
Generation Date Born Matured Retired Aptcrous Alate
1 . . . . . . . . . . . . . . . . . . . . . . .. May 13, 1926 May 19, 1926 5 5 I O

2 . . . . . . . . . . . . . . . . . . . . . . .. May 19, 1926 May 24, 1926 9 9 0

3 . . . . . . . . . . . . . . . . . . . . . . . . May 25, 1926 May 31, 1926 10 10 0

4 . . . . . . . . . . . . . . . . . . . . . . .. May 31, 1926 June 6, 1926 12 12 0

5 . . . . . . . . . . . . . . . . . . . . . . .. June 6, 1926 June 11, 1926 23 23 O

Paddock (6) reared 51 complete generations of Apltis gossypili using
practically the same methods in rearing the insects as those described
above. The primary object of this experiment was to determine the

  
  
  
 
   
  
  
    
  
 
  
 
   
  
  
  
  

8 BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

maximum number of generations of this species that were possible dur
ing one year at College Station. For this reason only the ﬁrst-bo ‘A
2 or 3 young of each mother Were transferred to an uninfested plan ;
which precluded any possibility of crowding. By selecting the aptero 5
form as the parent of each succeeding generation only one alate indi
vidual was obtained during the course of the entire generation series. i

The results of these two generation series experiments with Aph'
gossypii appear to be in exact accord With regard to the effect of parent,
age and ancestry on the ratio of forms produced. These observations .-
Which include the careful rearing of 110 generations, fail to give any in
dication that there is a tendency, in this species at least, for the Wing;
less parent to produce Winged offspring when reared under conditions i.
ample food andno crowding. V’

Further signiﬁcant results of an experiment pertinent in this con-
nection are reported by Comstock  page 417, who states:

“In an experiment conducted under my direction by Mr. Slingerland,
in the insectary at Cornell University, We reared 98 generations of the]
Wingless agamic form Without the appearance of any other form. The
experiment Was carried on for four years and three months Without any.
apparent change in the fecundity of the aphids, and Was discontinued
owing to the press of other duties. As the aphids were kept in a hot;
house throughout the Winters, seasonal inﬂuences Were practically elim-:
mated; and as members of each generation were placed singly on
aphid-free plants and their young removed as soon as born, there was
no crowding.” ‘

Summary of the Elfect of Parentage

During the period of twelve months 59 complete generations of the
Wingless agamic form of Aphis gossypii were reared in the laboratory
and insectary Without the appearance of any winged forms except in
three generations in which the aphids were allowed to become crowded
during development. The offspring of Winged parents matured Wholly?
Wingless forms throughout 5 complete generations counting from the.
winged stem mothers. In the light of these results, which are in exact
accord with those of a similar experiment with the same species, it’
appears logical to conclude: (a) that the normal tendency for this,
species is to be Wingless ; (b) that the production of wings is dependents
entirely upon environment inﬂuences. ~ ’

THE EFFECT OF NUTRITION

Nutrition as a factor affecting the forms of aphids produced has been
emphasized by several investigators. In fact, poor nutrition has been
assigned as the primary factor in determining the development of Wings A
in at least one species. ;

To determine the inﬂuence of starvation on the development of wings ,-
in Aphis gossypii, several series of starvation experiments Were con-v
ducted in which both young and adult aphids were used. The daily

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 9

period of starvation in all tests was 6 t0 8 hours. In case of the young
this was applied soon atter birth for varying periods ranging ‘irom 2
days t0 all through the time required for development.

Before referring to the data obtained in these experiments it should
be stated that no precautions were taken in any of the tests to prevent
crowding. The extreme importance of this factor in aﬁecting the
forms produced Was not fully appreciated at the time some of these ex-
periments were performed. While this may have affected the results
of some of the tests, however, this source of error should be practically
negligible since only small numbers of aphids were used in each indi-
vidual test.

A summary of the data obtained by starving young aphids for varying
periods during development is given in Table 3.

Table 3.——Effect of Starvation for Varying PeriodsfDuringDevelopment

Progeny Check Progeny
Parent No. of Period Starved -—
Tests Apterousl Alate Apterous’ Alate
A terous. . 10 First two days after birth. . . .. . . . 88 10 75 0
A ate. . . . . 5 First two days after birth . . . . . . . 34 4 21 O

Apterous. . 12 First three days after birth . . . . . . 74 1O 98 0

Alate. . . . . 3 First three days after birth . . . . . . 28 0 27 0

A terous. . 15 First four days after birth . . . . . . . 155 38 171 1

A ate. . . . . 5 First four da s after birth . . . . . . . 48 0 66 0

Apterous. . 19 All through evelopment . . . . . . . . 160 16 195 2

Alate. . . . . 8 All through development . . . . . . . . 55 0 91 0
Apterous. . 6 After third day to maturity. .. . . . 74 8 90 0

The inﬂuence of starvation on the forms produced is quite apparent
in the progeny of apterous mothers. Out of a total of 633 starved young
reared to maturity, 82 or 12.9 per cent were Winged as compared with
3 or 0.4 per cent of the 632i young reared as checks which were not
starved. However, when the progeny of alate parents was starved
during development the effect on the ratio of forms was not so pro-
nounced. In fact, in only one case did the winged form appear in re-
sponse to the imposed condition of starvation.

The data in Table 4 are presented to show the effect of poor nutri-
tion on the progeny of parents starved throughout the reproductive
period. The progeny produced in each test was well nourished from
birth to maturity.

Table 4.—Effect on Well Nourished Progeny of Starved Parents

_ _ Progeny
Parents Starved During Number Well Nourished Check Progeny
Reproductive Period of Tests
Apterous Alate Apterous Alate

Apterous . . . . . . . . . . . . . . . . . . . . . . . 28 64 31 79

Apterous . . . . . . . . . . . . . . . . . . . . . . . 15 26 3 49

Apterous . . . . . . . . . . . . . . . . . . . . . . . 15 47 4 55

Apterous . . . . . . . . . . . . . . . . . . . . . . . 10 31 12

Alate . . . . . . . . . . . . . . . . . . . . . . . . . . 28 64 2 64

Alate . . . . . . . . . . . . . . . . . . . . . . . . . . 15 41 0 44

<0
O
QQQUU-IC

1O BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

It will be noted that the offspring of apterous parents though well
nourished were inﬂuenced considerably by starving the parents. Out ; ‘
of a total of 218 young reared, 50 0r 22.9 per cent were alate; whereas 5
among the individuals in the check experiments only 6 or 2.1 per cent _
were alate out of a total of 2'79 young reared to maturity. Starving 1
alate parents, however, had very little inﬂuence in regard to the develop- »
ment of alate progeny. Only 2 winged individuals appeared in the 107 l

young reared in these experiments.

The inﬂuence of nutrition as a factor affecting the proportion of h
winged and Wingless forms in the well nourished progeny of parents _
starved during development and supplied with ample food after reach- g

ing maturity is shown in Table 5.

Table 5.——Effect on Well Nourished Progeny of Parents Starved During Development
and Well Nourished After Maturity

Parents Starved Through De- Progeny Reared Progeny Reared
velopment, Well Nourlshed Number Wel Nourished Check
Throughout Reproduction of Tests '

Period Apterous i Alate Apterous Alate
Apterous . . . . . . . . . . . . . . . . . . . . . . . 10 69 64 60 0

Apterous . . . . . . . . . . . . . . . . . . . . . . . 18 45 22 34 0

Apterous . . . . . . . . . . . . . . . . . . . . . . . 10 56 8 71 1

Apterous . . . . . . . . . . . . . . . . . . . . . . . 11 19 3 47 1

Alate . . . . . . . . . . . . . . . . . . . . . . . . . . 15 69 0 , 90 0

Alate . . . . . . . . . . ._ . . . . . . . . . . . . . . . 13 34 0 29 1

These results are especially interesting because they give some indi- I
cation of the inﬂuence of nutrition, under the most adverse conditions, ‘

on the ratio of forms produced. It will be noted in the data presented

above, that the effect of starvation during development is reﬂected by if
the appearance of many winged forms in the progeny of apterous par- a
ents even though the parents and young are well fed. Thus it is ap- A
parent that the lack of sufﬁicient nourishment during development pro-
duces a hold-over effect which becomes manifest by an increased number 3
of winged forms in the offspring of wingless parents. Similar tests .

with the progeny of alate parents produced negative results.

Summary of the Effect of Nutrition

From the data obtained in the starvation experiments with Aphis ‘_f
gossypii, it is obvious that nutrition may or may not affect the ratio of T.
forms produced, depending on the parent form. The results obtained in .
this connection appear to warrant the following conclusions: (a) A
that starvation increases the number of alate individuals in the progeny .
produced by apterous parents; (b) that starvation does not appear to "'
have any inﬂuence on the production of alate forms in the progeny pro- '
duced by alate parents; in other wordsthe offspring of alate parents I
revert to the normal tendency of the species, viz., the apterous form, I
with such puissance, that the effect produced by starvation in stimulat- ’

ing wing development is practically if not entirely counteracted.

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 11

THE EFFECT OF TEMPERATURE

Ewing (3) studying the effect of protracted parthenogenetic reproduc-
tion in Aphts a/venae made some incidental observations regarding the
inﬂuence of temperature on dimorphism in this species. In rearing
aphids under constant-temperature conditions he noted that at 60° F.
all the individuals produced Wings; at 65° F‘. or slightly above, only
the Wingless forms were produced; at 70° F. 15.1 per cent were Winged ;
at 80° F. 69.6 per cent were Winged.

This demonstration of the effect of temperature on Wing production
in this species is indeed a remarkable fact when considered in the light
of the complete inverse ratio of forms produced in a temperature varia-
tion from 60° F. to 65° F. or slightly above. Unless it is assumed that
the imposed condition of a constant temperature is too unnatural, the
question immediately arises, Will similar slight fluctuations in tempera-
ture under natural conditions produce like or even approximating re-
sults? This subject Will be considered in detail with reference to Aphis
gossyp/ii elsewhere in this paper.

Wadley (8) working with the same species used by Ewing, obtained
more or less conforming results in his experiments on the effect of tem-
perature, although the data presented are much less impressive than
EWing’s. At 62" F. only 15.1 per cent Were Winged; at 65°  1.3
per cent W6l‘€ Winged; at 70° F. 2.3 per cent produced Wings; at 80° F.
only 6.5 per cent produced Wings.

Ewing (4) discussing the factors of inheritance and parentage_as
affecting aphid forms produced, elaborated the conclusions presented in
his earlier paper on the effect of temperature, in the light of Wadley’s
results. He notes that there is a summation effect of parentage on the
offspring of a generation of aphids, depending upon the number and
nearness of the ancestors of either form. This is suggested as the ex-
planation for the apparent differences occuring between the results of
the temperature experiments cited above. In other Words he concludes
that the effect of temperature on the ratio of the agamic forms produced
is more precisive in aphids having an apterous monomorphic parentage
of 16 or more generations.

For the purpose of studying the effect of temperature on Wing de-
velopment in Aphis gossypii a Freas Electric Oven With a constant tem-
perature regulator Was procured. This oven, which contains a large
compartment (34”x24”X17”) lighted by four small windows, and in
which temperature and humidity conditions could be controlled Within
certain limits, seemed ideally suited for this purpose.

Such did not prove to be the case, however, for it Was found impos-
sible to rear even a single generation of aphids under optimum condi-
tions of temperature and humidity. For some unknown reason this
species Was found unable to tolerate conﬁnement Within the oven and in-
variably succumbed before any effects of temperature could be noted.
Very likely the greatly subdued light proved to be a condition too un-
natural for the insects to withstand for any extended period of time.

  
   
 
  
 
 
  
 
 
  
  
  
 
 
 
  
 
 
  
  
 
 

12 BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

After numerous attempts t0 rear the insects within the oven had faile
the studies were conﬁned to the laboratory and insectary. ,

The generation series experiment referred to above was in reality '
compound experiment in that all the factors herein discussed as affec .
ing the ratio of aphid forms produced were considered and controllei
within reasonable limits for part of or the entire duration of the ex
periment. .

From October 10, 1925, to May 20, 1926, the experiment was co
ducted in a large well lighted laboratory. During this time the tem_
peratures were fairly well controlled; at least the aphids for the mos
part were not subjected to any sudden or very great changes in tem.
perature. Frequently the daily variation was not more than 3° or 4° j
and within the ‘limits of 8° or 10° F. during the period of a week o
more. Thus it was often possible to rear a complete generation o
aphids under these conditions. .

The effect of temperature on the ratio of forms produced in the labor f
tory is shown in Table 6. In this connection it is important to no .1‘
that these data refer to aphids of a known apterous monomorphic par i
entage of 16 to 35 generations reared under conditions of ample foo
and practically no crowding. The maximum and minimum tempera;
tures given are those occurring during the entire period required for th
development of each generation and the mean temperature given is th
average of the bi-hourly readings taken during the same period o
time. 1

Table 6.—Effect of Temperature on the Ratio of Forms Produced in the Laboratory

  

Isola- Apterous Period of Temperature Number Ratio of Forms a
tion Monomorphic Development _ Reared
No. Parentage Max. Min. Mean Alate Aptero _
1926

1 16 generations Jan. 29-Feb. 3. . . . . 91 7O 78 .8 7 O 7.
2 17 generations Feb. 3-Feb. 8 . . . . . . 86 70 77 .7 27 0 27
3 18 generations Feb. 9-Feb. 14. . .. . 77 65 72 .9 81 6 75
4 19 generations Feb. 15-Feb. 20. . . . 75 64 71 .1 16 O 16
5 2O generations Feb. 21-Feb. 26. . . . 78 66 74 .2 19 0 19
6 21 generations Feb. 26-Mar. 3.. .. . 85 67 75 .3 19 O 19
7 22 generations Mar. 4-‘VIar. 9. . . . . 78 68 73 .4 27 0 27
8 23 generations Mar. 10-Mar. 15. . . 8O 63 71.3 29 7 22
9 24 generations Mar. 16-Mar. 21. . . 81 68 75 .6 17 O 17
10 25 generations Mar. 22-Mar. 28. . . 80 61 72 .0 25 0 25
11 26 generations Mar. 29-April 3. . . . 8O 63 71 .2 21 O 21
12 27 generations April 4-April 9. . . . . 84 65 75 .3 9 0 9
l3 28 generations April 10-April 15. . . 75 65 70 .9 22 0 22
14 29 generations April 16-April 21. . . 77 68 73.1 11 0 11
15 30 generations April 22-April 26 . . . 78 71 74 .7 1O 0 1O
16 31 generations April 27-May 2. . . . 77 72 76 .0 18 O 18
17 32 generations May 2-May 7 . . . . . . 79 74 77 .8 17 0 17
18 33 generations May 7-M_ay—12. . . . . 85 76 81 .3 17 0 17
19 34 generations May 12-May 17. . . . 82 73 77 .5 15 0 15
*2O 35 generations May 17-May 22. . . . 85 6O 75 .8 12 O 12

*In insectary on May 20, 1926.

From these data it will be observed that there is no correlation be-i
tween temperature and the ratio of forms produced in this species. In
mean temperatures ranging from 709° F. to 813° F. with extremes

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 13

ﬂuctuating between 5° F. and 21° F., the apterous forms continued to
predominate. In fact, the winged forms appeared in but two isolations
and these, as has already been explained, were attributable t0 crowding
and certainly not t0 any inﬂuence of temperature, since the aphids
reared under approximately the same temperature conditions in all
other isolations were wholly apterous.

From May 20, 1926, to October 10, 1926, the generation series ex-
periment was conducted in the insectary, where temperatures approxi-
mated natural conditions. The aphids reared during this time were thus
exposed to considerable daily ﬂuctuations of temperatures all through de-
velopment. The range between the daily maximum temperature and the
daily minimum temperature often extended from 15° F. t0 20° F. or
more, and these environmental conditions appeared extremely favorable
for making observations on the eﬂect produced by approximately natural
variations in temperatures, with respect to the development of wings in
this species.

The data obtained from this portion of the experiment are presented
in Table '7. It should be noted that the aphids referred to in these data
had an apterous monomorphic ancestry of 36 to 58 generations and that
all were reared under conditions of ample food and no crowding. The
maximum and minimum temperatures given in each case represent the
extremes to which the individuals of each isolation were subjected, and
the mean temperature is the average of bi-hourly readings taken during
the tirnr required for development of the aphids in the corresponding
isolation.

Table 7.—Eﬂ‘ect of Temperature on the Ratio of Forms Reduced in the Insectary

Isola- Apterous _ Temperature Number Ratio 0f Forms
tion Monomorphic Period of _ Reared ——-—~———~——
No. Parentage Development Max. Min. Mean Alate Apterous

_ 1926
21 36 generations May 22-May 27. . . . 87 64 76 .1 15 0 15
22 37 generations May 27-June 1. . . . . 9O 67 78 .7 13 0 13
23 38 generations June 2-June 8 . . . . . . 92 62 77 .1 14 0 14
24 39 generations June 8-June 13.. .. . 93 71 80 .7 13 0 13
25 40 generations June 14-June 20. . . . 96 73 84.6 15 0 15
26 41 generations June 20-June 25. . . . 96 72 82 .3 13 0 13
27 42 generations June 26-July 1 . . . . . 93 70 80 .9 14 0 14
28 43 generations July 2-July 8 . . . . . . 97 7O 83 .7 15 O 15
29 44 generations July 9-July 14. . . . . 96 69 82 .0 14 0 14
30 45 generations July l5-July 20. . . . 93 66 81 .4 13 0 13
31 46 generations July 20-July 25. . . . 92 71 8O .8 15 O 15
32 47 generations July 26-July 31. . . . 97 73 85 .7 16 0 16
33 48 generations July 31-Aug. 5.. . . . 98 73 85 .9 17 0 17
34 49 generations Aug. 6-Aug. 11. . . . . 102 73 87 .2 13 0 13
35 50 generations Aug. 12-Aug. 17... . 98 74 84 .5 12 0 12 \
36 51 generations Aug. 18-Aug. 25. . . . 101 69 85 .9 12 O 12
37 52 generations Aug. 26-Aug. 31. . . . 94 67 8O .0 14 0 14
38 53 generations Aug. 31-Sept. 6. . . . 99 79 86.5 13 0 13
39 54 generations Sept. 7-Sept. 14. .. . 100 79 88.8 16 0 16
40 55 generations Sept. 14-Sept. 20. . . 99 77 87 .8 11 O 11
41 56 generations Sept. 21-Sept. 26. . . 99 64 88 .1 15 0 15
42 57 generations Sept. 26-Oct. 2. . . . . 99 65 83 .2 13 0 13
43 58 generations Oct. 2-Oct. 8 . . . . . . . 98 61 82 .1 9 0 9

14 BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

In comparing the temperatures occuring during this experiment with
those given in Table 6, it will be noted that the range between maximum
and minimum is usually much greater, and that the mean temperature
also is consistently higher, in fact, averaging well above the temperature

, reported as effective in regard to the stimulation of wing development.

However, not a single alate form appeared among all the aphids, of a
long apterous monomorphic parentage, which were reared in this experi-

merit.
Summary of the EEect of Temperature

In the data presented above it has been shown that the ratio of forms
was not affected by temperature among 20 generations, which included
432 individuals, reared in the laboratory from January 29, 1926, to
May 22, 1926, during which time the average mean temperature was
748° F. Two isolations reared in a mean temperature of 76.0° F. and
'77.8°F., respectively, with the ﬂuctuations within the limits of 5° F.,

as well as many other isolations reared in comparable mean temperatures 
with the ﬂuctuations ranging from 10° F. to 20° F. matured 100 per 

cent apterous forms.

Similarly, the forms produced were not affected by temperature in the
23 generations, which included 315 individuals, reared in the insectary
from May 22, 1926, to October 8, 1926, during which time the average
mean temperature was 83.2° F. The apterous form continued to pre-

dominate in mean temperatures as high as 88° F. regardless of daily or i

extreme ﬂuctuations ranging from 20° F. to 35° F. during the develop-

mental period of a generation.
In the light of these results it appears logical to conclude: that tem-
perature within the limits of 70° F. to 90° F. does not affect the ratio

of forms produced in this species.

THE EFFECT OF CRO\VDING

The inﬂuence of crowding as a factor affecting wing development in
aphids has been studied by several investigators. Most frequently

crowding is discussed in connection with poor nutrition, the assumption '

being that aphids crowded on plants obtain insufﬁcient nourishment and
that the Winged form appears in response to this stimulus. The results

of these studies, however, indicate a wide difference of opinion regard- ii
ing the relative importance of. crowding in affecting the proportion of 7

aphid forms produced. ~

Baker and Turner (1) working with Aphis pomi found that poor ,
nutrition as a result of heavy infestations of this species did not cause -

the alate form to appear. They state:

“The theory has been frequently advanced that the production of i
winged forms during the summer is due to a lack of sufficient nourish- 7
ment for the insects. In some cases the wording of this theory is modi- i
fled by the statement that winged forms appear on plants which are

very heavily infested. The writers’ results are a ﬂat contradiction

of this theory for this species. As has been stated previously, in hand- ‘

INFLUENCES 0N WING PRODUCTION IN APHIS GOSSYPII, GLoVER 15

ling the insects the Writers always transferred the mothers t0 new
plants, rather than the progeny. In this way several consecutive gen-
erations were reared on one plant. Thus the effect of- poor or good food
would be accentuated. Yet the Winged forms were never obtained in
series of small, poorly fed insects, but occurred frequently in Well-nour-
ished series.”

Comstock (2) after rearing 59 consecutive generations of the agamic
apterous forms states:

“In order to determine the inﬂuence of crowding, members of the six-
tieth generation Were placed on separate plants and their young not
removed. At the end of three Weeks the Winged agamic forms ap-

-peared, evidently in response to need of migration to less densely popu-

lated plants; While in other cages Where the young were removed
promptly, no migrants appeared up to the end of the experiment.”

Before referring to the results of any observations on the effect of
crowding in this species it appears desirable to deﬁne the term as con-
sidered in this paper. Crowding is a relative condition which varies
from a comparatively small colony of aphids situated in contiguous
positions within a restricted area, to a maximum infestation in which
the insects cover practically the entire stem, petiole or leaf of the food
plant.

In these studies of Aphis gossypiiit Was noted that a high percentage
of the alate form occurred invariably on plants which were heavily in-
fested. Several series of experiments were conducted, therefore, to
determine the influence of crowding on wing development in this species.
It has already been noted above in the generation series experiment,
Table 1, that the winged form failed to appear when crowding did not
occur and that no difficulty was experienced in maintaining an apterous
lineage for 59 generations under these conditions. Members of 10 sep-
arate generations of this series were isolated on uninfested plants and
their progeny allowed to multiply without disturbance until a crowded
condition occurred. It will be noted in Table 8, that the alate form ap-
peared in every case.

Table 8.——Eﬂ"ect of Crowding Progeny on WinglDevelopment

_ First Young Winged Forms, Check, Progeny
(xencr- Date Number Observed After Progeny Not Crowded
atlon Parentagc Isolated Isolated Developing ell —~———-—--—
Wings Crowded Apterousl Alate
1925 1926
8 Apterous.... Dec. 9 9 Jan. 9........Many......... 25 O
1O Apterous. ... 131635620 17 Jan. 15... .. . .. Many . . . . . . . .. 19 O

13 Apterous.  Jan. 9 11 Jan.20..... Few . . . . . . . . .. 32. 4

18 Apterous. ... Feb. 1O 20 Feb. l6 . . . . . .. Many... . . . .. . 75 6

19 Apterous. . . . Feb. 16 65 Feb. 24 . . . . . . . Predominate. . . 16 O

29 Apterous. . . . April 17 19 April 23 . . . . . . . Few . . . . . . . . . . 11 0

47 Apterous. .. . July 25 l3 Aug. 9 . . . . . . . Few . . . . . . . . . . 16 0

48 Apterous. ... July 28 10 Aug. 18 . . . . . .. Many... . . . ... 17 0

55 Apterous. . . . Sept. 15 9 Sept. 23 . . . . . . . Many . . . . . . . . . 11 O

59 Apterous. . . . Oct. 3 9 Oct. 19 . . . . . . . Few- . . . . . . . . . . 14 0

  
 
 
 
  
    
    
 
  
  
  
  
   
    

16 BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

The individuals used in each check of these experiments were sis =
to those isolatedfor observation in the corresponding generation. I‘,
they had the same parentage and ancestry, and their oifspring W
reared under comparable environmental conditions except as to cro‘
ing. In only two instances did the alate form appear in the che 
and it may be safely assumed that these were the direct results
crowding, since a considerably larger number of young were rear
making it more diﬂicult to prevent the aphids, especially when v
young, from feeding in contiguous situations. _ }

In another experiment apterous individuals of an unknown pare
age were placed on uninfested potted plants in the laboratory :
allowed to reproduce for several generations. After these plants {a
become densely populated with aphids the adults and latter ins
nymphs were removed daily and a record made of the number of wing
and Wingless forms. These data are presented in Table 9.

Table 9.—Effect of Crowding Parents and Progeny on Wing Development

a 2-0, and the ﬁrst-born young reached maturity _by January 26, before

  
   
  
  
  
 
  
  
  
  
  
 
  

Check, ,

Number Progeny Not Crow

Test Date Mature Apterous Alate -——i—- _
Apterous Alate »

1924
1 . . . . . . . . . . . . . . . . . . . . . Mar. 29 29 12 17 31 2

2 . . . . . . . . . . . . . . . . . . . .. Mar 30 41 15 26 23 0

3 . . . . . . . . . . . . . . . . . . . . . Mar. 33 12 21 16 O

4 . . . . . . . . . . . . . . . . . . . .. April 1 27 21 6 19 0

5 . . . . . . . . . . . . . . . . . . . . . April 2 26 12 14 14 0

6 . . . . . . . . . . . . . . . . . . . .. April 3 18 15 3 0

7 . . . . . . . . . . . . . . . . . . . . . May 6 43 19 24 12 O

8 . . . . . . . . . . . . . . . . . .  May 7 28 11 17 21 0

9 . . . . . . . . . . . . . . . . . . . . . May 8 33 20 13 17 0

10 . . . . . . . . . . . . . . . . . . . . . May 9 41 16 25 14 O

11 . . . . . . . . . . . . . . . . . . . . . May 10 39 20 19 16 0

12 . . . . . . . . . . . . . . . . . . . . . May 11 21 16 5 27 3

13 . . . . . . . . . . . . . . . . . . . . . May 12 18 11 8 O

14 . . . . . . . . . . . . . . . . . . . . . May 13 41 21 2O 12 0

The inﬂuence of crowding as a potent factor affecting the forms pr
duced is shown by these data. Out of a total of 488 aphids noted, 22
or slightly more than 5O per cent were winged, while only 5 winge
forms appeared among the 243 individuals reared in the checks 
which crowding was practically eliminated. ,

To determine if crowding is likewise effective in altering the rati
of forms produced in the progeny of alate parents, 10 nymphs destin
to become winged were isolated January 18, 1926, on a young cotto
plant in the laboratory. These individuals were descendants of apte
ous parents for eight generations. Reproduction began on J anua

crowded condition occurred. There were no alate forms in the progen’
of these alate mothers. In the succeeding generation, however, .
crowded condition was apparent by January .30. Many nymphs wi f a
developing wings were visible on February 2, and two days later i
was estimated that practically one-third of the entire population, whic

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 17

consisted of a hundred or more aphids, were winged or destined to
become so.

In a parallel experiment to check these results, the progeny of alate
mothers, which were sisters to those referred to in the experiment de-
scribed above, continued to approach 100 per cent Wingless forms in
the succeeding generation when crowding was not permitted to take
place. Out of a total of '79 aphids reared only 3 were winged.

All efforts to determine the effect on the progeny of crowded alate
parents proved unsuccessful. The winged forms of this species refused
to tolerate any crowding and migrated from the plants to the sides of
the cages, where they starved in preference to returning to the plants
for food. '

Some references to the effect of crowding on wing production in
aphids embrace the theory that the insects located on heavily infested
plants obtain insufficient nourishment, and that hence poor nutrition
is the primary cause for the appearance of the alate forms. In these
studies of Aphis gossypii, however, frequent observations were made
which appeared at variance with this explanation. For instance, com-

paratively small colonies of aphids with the individuals situated closely -

together along the stem of a young succulent plant, on a leaf petiole,
or even on a leaf, were found often to contain a high percentage of
winged forms even though the infestation was not very heavy nor did the
plants show any visible effects resulting from the feeding of the insects
so far as wilting or any lack of vigorous appearance is concerned.

Several tests were made to ascertain if crowding becomes an effective
factor in stimulating wing development in this species primarily be-
cause it results in a depletion of the food supply. In each of these
tests two heavily infested leaves of a cotton plant attached to the same
branch were selected and all the aphids carefully removed. Immedi-
ately after the leaves were freed from all the insects 4 or 5 apterous
individuals of a known apterous parentage were placed on one leaf
and 30 to 40 comparable individuals on the neighboring leaf. In the
former case the progeny produced were not allowed to become crowded
at any time during development, while in the latter case none of the
progeny were removed and a crowded condition thereby encouraged.

The results of these tests proved to be in accord regarding the fol-
lowing points: (a) the progeny of apterous parents will approach 100
per cent apterous if not crowded during development, when reared on a
leaf that has sustained a heavy prior infestation; (b) the offspring of
apterous parents which were reared on a leaf previously infested will
approach 100 per cent apterous if not crowded during development;
(c) the time required for the appearance of the alate form in the
crowded progeny of apterous parents reared on a leaf previously in-
fested by many insects, is practically the same as in case of no prior
infestation of the food supply.

From these observations it will be noted that any changes wrought
by the feeding of a dense population of this species, either in the
amount or chemical composition of the food, available to the aphids

  
 
  
 
 
 
  
  
 
  
 
  
 
 
 
  
 
  
 
 
  
 
 
 
  
 
 
 
  
 
 
  
 
 
  

18 V BULLETIN NO. 353, TEXAS AGRICULTURAL EXPERIMENT STATION

subsequently placed thereon, did not manifest itself by affecting th
ratio of forms produced. 

Since the metabolic processes of a plant in manufacturing and stor-
ing up food elements are rather slow processes, any changes in th‘
amount or character of food in a leaf resulting from the feeding of
many insects will remain present for an indeﬁnite period of time;
However, since the ratio of forms of aphids reared on a food suppl
which had sustained a prior heavy infestation of insects, was no
affected toiany appreciable degree, it appears that crowding embraces
another factor or factors through which it may become effective 
stimulating wing development. l i

Summary of the Elfect of Crowding

- In the data presented above it will be observed: that in rearing in#
dividuals of Aphis gossypii of a known apterous monomorphic parent<
age of 16 generations or more under conditions of ample food and either
fairly uniform or widely ﬂuctuating temperatures, crowding during
development resulted in an increased number of winged forms in every
case; that the ﬁrst generation offspring of the progeny of alate parents
when reared under similar conditions, also contained a higher percent-
age of Winged forms. The very positive effect of crowding aphids dur-;
ing development, on the ratio of forms produced under practicall
any given set of conditions indicates the conclusion: that crowding is
a very potential, if not the dominant or controlling factor, in stimué
lating wing development in this species. v

OBSERVATIONS ON THE EFFECT OF HUMIDITY

During the entire extent of the generation series studies, i. e., from
October 10, 1925, to October 10, 1926, relative humidity conditions-
Were recorded in conjunction with the temperatures. While the degree
of ﬂuctuation of the relative humidity in the laboratory frequently was
greater than in case of the temperatures for the same period of time,-
nevertheless, it was often fairly uniform for periods of three or foul?
consecutive days. When the relative humidity dropped below 4O per"
cent the aphids developed more slowly, but no winged forms appeared’
in response to this condition. In the insectary, Where the tempera-
tures approximated natural conditions, the per cent of relative humid-*
ity often ranged from 88 to 41 per cent in a 24-hour period; averaging
from 60 to 70 per cent for periods of more than a week. When aphids
were reared under these conditions, no correlation was found to exist
between the per cent of relative humidity and the ratio of alate t0
apterous forms produced.

INFLUENCES ON WING PRODUCTION IN APHIS GOSSYPII, GLOVER 19

CONCLUSIONS

 1. The normal tendency in Aphis gossyp-ii is to produce offspring
é which do not develop Wings.
i; 2. The production of wings is dependent entirely upon environ-
" mental inﬂuences. ‘

3. Starvation increases the number of Winged forms in the progeny
produced by apterous parents.

‘l. The offspring of alate parents revert to the normal tendency of
the species, viz., the apterous form, with such puissance, that the effect

   
 
 
   
  
  
 
  
 
 
  

'§ if not entirely counteracted.
_. 5. Temperature Within the limits of 70° F to 90° F. does not affect
 the ratio of forms produced in this species. '
_. 6. Crowding is a very potential, if not the dominant or controlling
 factor in stimulating Wing development in Aphis gossypii.
 7. There is no correlation between the prevailing relative humidity
 in which the aphids are reared and the ratio of alate to apterous forms
produced. I
* - LITERATURE CITED
}(1) Baker, A. (1., and Turner, W. F. - r
r- 1916. Morphology and Biology of the Green Apple Aphis.
 Jour. Agr. Res, Vol. 5, No. 21, pp. 955-990. '
 Comstock, J. H.
. 1921. An Introduction to Entomology, p. 417.
Ewing, H. E.
1916. Eighty-seven Generations in a Parthenogenetic Pure
Line of Aphis avenue Fab. Biol. Bul., Vol. 31,
No. 1, pp. 53-112.
'Ewing, H. E. .
1925. The Factors of Inheritance and Parentage as Affect-
‘ ing the Ratio of Alate to Apterous Individuals
in Aphids. Amer. Nat, Vol. 59, pp. 311-326.
Gregory, Louise H.
1917. The Effect of Starvation on the Wing Development of
lllicrosiphum destmctor. Biol. Bul., Vol. 33, pp.
296-303.
Paddock, F. B. .
1919. The Cotton or Melon Louse: Life History Studies.
TeX. Expt. Sta. Bul. 257.
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produced by starvation in stimulating wing development is practically