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opy 1 The University of Chicago

THE RELATION OF WATER TO THE
BEHAVIOK OF THE POTATO
BEETLE IN A DESERT

A DISSERTATION
SUBMITTED TO THE FACULTY
OF THE OGDEN GRADUATE SCHOOL OF SCIENCE
IN CANDIDACY FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

DEPARTMENT OF ZOOLOGY

BY
JOSEPH KUMLER BREITENBECHER

Private Edition, Distributed By
THE UNIVERSITY OF CHICAGO LIBRARIES
CHICAGO, ILLINOIS

Reprinted from
PUBLICATION 263 OF THE CARNEGIE INSTITUTION OF WASHINGTON
PP. 341-84

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The University of Chicago

THE KELATION OF WATER TO THE
BEHAVIOK OF THE POTATO
BEETLE IN A DESERT

A DISSERTATION

SUBMITTED TO THE FACULTY
OF THE OGDEN GRADUATE SCHOOL OF SCIENCE
IN CANDIDACY FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

DEPARTMENT OF ZOOLOGY

BY
JOSEPH KUMLER BREITENBECHER

Private Edition, Distributed By
THE UNIVERSITY OF CHICAGO LIBRARIES
CHICAGO, ILLINOIS

Reprinted from
PUBLICATION 203 OF THE CARNEGIE INSTITUTION OF WASHINGTON
Pp. 341-84

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THE RELATION OF WATER TO THE
BEHAVIOR OF THE POTATO
BEE TLE IN: A. DESERT

BY

J. K. BREITENBECHER
OF THE BIOLOGICAL LABORATORY OF WESTERN RESERVE UNIVERSITY

[Extracted from Publication 263 of the Carnegie Institution of
Washington, pages 341- 384. |

CONTENTS.

PAGE
MTV GT OGUICCTOMN lore onset ice alate xi 09: ore co tere) ere Ai oles en's) oe olive l@n@ & collells Foire lei/s¥ elle) e!\eal ei'etiel avavinl «ele ctetats 343
Instrumentation and conditions of experiment ...........2.. ccc cece eee n eens 343
IVIALOT AUS ters aces feneietotate ereueletarsctousts gio: 1s atl do:ssleide 6 GG SOs oa wile ere Aialinle elavaleleoicteteler 344
RoleOor water in LEPLOGUCTLVE ACULVILY. << ixio- olcrere icles alelel> ete ie ouele laters otelsieiele </ete are 346
Experiments with soil Moisture ... 2.0.0.0 cc es ec eccscesesecsescccsesenes 348
Experiments with Cvaporation tates! 22.2 cians 6 oieiia oe) sleuisieietel ciel ate, siete 349
Rolevol waterin the preservation: Of WLC ec cic. ooo s1e 01010 1o'/'o) oo auctioneers eee tener 350
Relation of water-loss in insects when exposed to changes in the relative
humidity of the surrounding medium, and its effect on the activities
OL SUCH OLLAMISINS vs e.c'et. e ioys © cious oie fis el lle ve/s'e w/e, «lakala'e is ste pielegeted teeters 354
Experiments upon evaporation, transpiration, and behavior .............. 355
Réle of water in hibernation ...........secccccee we, RiSse ene Aimer See teleost eee 366
Entrance into hibermationy fies « «2c « afc01s cu eso ee averer)sGrelieters ciel ellape a eeielelenete 366
Activaties: QUnine Ni beGTMmatlon) jcc-« aicis.2-«! .cieleis oie ere: sie oie eye oles oars euetotere eteteteneret 371
Water relation of soils and hibernating beetles ............ ccs cece eevee 371
Hmergence from WiDSCTN ATION 65.6 6 cs 05 55 oic o.c.c16 scene owes 9 msi eiellelslioel#/(sl'sisi' 6 372
Summary and discussion upon the relation of water to hibernation ...... 313
Effect of changes in water content upon alterations in tropic activities........ 375
Experiments upon the role of water in geotropism ...............0e 0000s 376
Relation of temperature to outgo and intake of water............ cee e eee e eens BYETl
Metabolism ‘and! water Telation: sé \.0.6:c/c.6.<ew ate erelelererciaisl oie eietetwie eielc + eis telel sreterersteneis 378
General discussion upon the role of water in living things ................... 379
Summary and conclusion ..... a chieeR etree sSialta arene aravayevafelestenenetecotastuenerapaesnereierevate ss . 881

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THE RELATION OF WATER TO THE BEHAVIOR OF
THE POTATO BEETLE IN A DESERT.

INTRODUCTION.

In a series of experiments maintained by Professor Tower to determine the
action of the Tucson Desert upon evolutionary processes in chrysomelid beetles,
it was observed that soil-moisture, humidity, and the like played an important
role in modifying the activities of these organisms when introduced into the
arid region; so, as a result of these observations, the author undertook a series
of investigations to discover any possible connection between this water-relation
and the reactions of the potato beetle, Leptinotarsa decemlineata (Say), when
transplanted into the desert from a temperate habitat.

A large stock of this species was sent to Tucson from Chicago in June 1911,
so that comparative studies under different environmental complexes could be
made. Three cultures were established in several open-air breeding-cages at the
stations already equipped for Professor Tower at Tucson and Chicago. Two of
these stations, which were arid in character, are designated as Tucson Station A
and Tucson Station B, while the third one, known as the Chicago Station, was
temperate and located at the University of Chicago. The former of the two
desert stations was situated at the base of the northern slope of Tumamoe Hill,
just within the flood-plain of the Santa Cruz River, at an altitude of 2,370 feet,
while the latter was located on the shoulder of this hill, on which the Desert
Laboratory is situated, at an elevation of 2,705 feet. The biological significance
of the conditions at these stations, as indicated, is given elsewhere, and the
problems dealt with concern the relations which exist between the activities of
the beetles when allowed to reproduce at these localities and the changes pro-
duced in the water-content of the animals through the action of the various
environmental factors.

INSTRUMENTATION AND CONDITIONS OF EXPERIMENT.

At each station the evaporation rates were obtained by the Livingston at-
mometers, and Friez self-recording thermographs were employed to measure
the temperatures, air and soil, and the same maker’s hygrographs were also
used for the relative humidities; these instruments were calibrated and stand-
ardized fortnightly. The rainfall-readings were obtained from a standard
weather bureau rain-gage at the Laboratory site. It is interesting to notice that
the environmental data as recorded from these experiments showed for the arid
complex that the greatest daily fluctuations occurred at Station A and the
highest evaporation at Station B, while the lowest evaporation-rates and air-
temperatures were at Station C. The Tucson region as a whole, when contrasted
with the Chicago conditions, has a higher rate of evaporation, a lower relative

343

344 RELATION OF WATER TO THE BEHAVIOR OF

humidity, a stronger light intensity, and a wider daily fluctuation in both air
and soil temperatures ; excessive nocturnal radiations and convectional currents
were also potent factors in the desert.

Four seasons were apparent in the arid region: A winter rainy season extend-
ing from November until April; a dry fore-summer season, from April until
July ; a midsummer rainy season, from July until the middle of September ; and
a dry after-summer season, from the middle of September until early in Novem-
ber. At Chicago rain occurred throughout the year. The annual rainfall from
several years’ data was about 12 inches at Tucson and 30 at Chicago. The
monthly records for both stations are given in Table 1 for the three years during
which these experiments were in progress.

TABLE 1.

.| Jan. | Feb. | Mch.| Apr. Oct. | Nov. | Dec. | Total.

Station.

0.08/1.74/0.06/12.62
1.23) T. |0.85)11.25
1.78/0.00/0.39) 9.84

m— obo

191011.00! T. | T. |0.05| T. |0.22/4.20
Tucson.......

1911/1. .99/0.25|0.27 0.00,0.07)1.57
| 1 :
1.79)1.31/1.32/26.86
3,79|3.27 |2.54/33.83
3.52)1.45/1.08/29. 67

(SS) one

ane oom
Oo mm CO ono

wNnos Conan

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awo

eo eter

Notre.—The rainfall records at Tucson were obtained from a standard Weather
Bureau rain-gage at the Laboratory site. The Chicago data were taken from the
records of the Weather Bureau.

MATERIALS.

The potato beetles were collected in May 1911, near Chicago, as they emerged
from hibernation, and were allowed to breed there as a group-culture within a
large cage filled with potato plants until late in June. A part of this material
was then sent to Tucson, where it became the progenitor of the animals used
in the majority of the experiments. Organisms when collected from nature are
often hybrids, so that crossing of different generations may have taken place, but
for complete breeding-records and life-histories of stocks used see Table 2, which
shows that these materials reacted homozygously. A brief description of their
activities follows.

At Tucson Station A these stocks were received on June 26, 1911, and
immediately bred as a group-culture, so that 1,328 adults were produced in 25
days, giving generation I. After feeding upon the potato plants for a few days,
these first-generation individuals were bred as a group-culture and produced
generation IT, numbering 2,312 progeny, in 26 days. Many of the beetles of this
second generation provided the materials for a large number of the hibernation
experiments which were carried on in 1911, but many of the emerged animals
were allowed to hibernate during the winter of 1911-12 as stock for work during
the following year. When, in June, water was added to the soil within the cage,
the organisms emerged from hibernation as a group-culture, which in 29 days
gave generation III, of 1,743 offspring. From this material 50 females and
50 males were mated and allowed to breed at random, giving generation IV, of
4,049 progeny, in 26 days. For the above data, see Table 2.

Tur Potato BEETLE IN A DESERT 3845

At Tucson Station B the parent group of 104 adults for this culture was
received on July 15 and bred as a group-culture, producing 204 offspring in
25 days, thus giving generation I. As soon as the adults from the first genera-
tion appeared they were removed to another breeding-cage, but they immediately
burrowed into the ground within the experimental cages and hibernated there
until September, when they began breeding and in 21 days produced generation
II, of 293 progeny. A few days after emerging from pupation all of the beetles
went into hibernation without feeding, where they remained until the following
summer, when, on May 31, 7 males and 16 females emerged and bred immedi-
ately, giving generation III of 283 adults in 31 days. These were allowed to
reproduce as a group-culture, giving in 31 days generation IV of 127 offspring.

TABLE 2.
Year, station, and Duration of Period of First Second Third
generation. breeding. oviposition. stage larve. stage larve. stage larve.
1911, Tucson A, g.I..... June 26-July 17} July 7-19...... July 12-21..... July 13-27..... July 17-31.....
1911, Tucson A, g. II....| Aug. 1-18..... Aug. 4-22...... Aug. 10-26....} Aug. 16-31..... Aug. 22-Sept. 1
1912, Tucson A, g. IIIT ..} Autumnof 1911] June 4-15..... June 12-21....| Jume 15-28..... June 18-30....
1912, Tucson A, g. IV...| July 8-29...... July 15-29..... July 17-Aug. 2| July 20-Aug. 5| July 25-Aug. 8
1911, Tucson B, g. I..... July 15-23..... July 17-23..... July 21-29..... July 23-Aug. 2) July 27-Aug. 6
1911, Tucson B, g. II....} Sept. 3-7...... Sept. 8-7...... Sept. 5-11. ..0% Sept. 7-19......| Sept. 11-21....
1912, Tucson B, g. IIL...) May 31-June 20) June 5-20..... June 14-25..... June 16-30..... June 20-July 10
1912, Tucson B, g. [V...| July 10-Aug. 12) July 24-Aug. 12] July 27-Aug. 14} Aug. 4-27...... Aug. 12-29.....
LOM CHICA LO Sa Weis ssats'el|| wa cand sre Garcisinas UNE GLO sacaatell) asides a:0'p cree esl), op ecieleeleieisis, gia =i]! ua eistew e ciee s/s \aie'eie
POT Chicago Ga lla ceus's|: eee sacewsissiace's ARUN erenicle—llis se resevar| (uae ie eiatctaler oft; ¢iatstatellilile ere! ciereie wratetatae'eiall Meisaler/a\ seis s/erriar
I91S (Ohicago es Weve cece se eseseeess APUILE) 21.9; caroriell! a wiv enieraigie bile nleiolll clots ciate 6, e1sicleie’aie'|| yavorn:farale.e wren elphe
TOON CAFO ELV acne || cadwasmowoenicee AUR: TAL ce cce| isesencaacusdusis| eece eines Fade co\lainea ces on SoReae
Year, station, and Pupa Emerged as No. of Adults Duration of
generation. state. adults. adults. hiberniated. life cycle.
1911, Tucson A, g. I.....| July 19-Aug. 1] July 31-Aug. 14 1328 NON isc sesines 25-26 days.
1911, Tucson A,g II....| Aug. 26-Sept. 2] Sept. 2-13..... 2312 Over winter...| 22-29 days.
1912, Tucson A, g. IlI...| June 21-July 8] July 4-16...... 1743 NOM Careica sens as 28-30 days.
1912, Tucson A, g. IV...| July 29-Aug. 11] Aug. 8-26...... 4049 OGia aviateoamnes 24-28 days.
1911, Tucson B, g.I..... July 29-Aug. 8} Aug. 10-18..... 204 Aug. 18-Sept. 3} 25-26 days.
1911, Tucson. B, g. II....| Sept. 12-22....] Sept. 19-29.... 298 Sept: $0) <ce0; 20-22 days.
1912, Tucson B, g. III...} Jume25-July 15) July 10-23..... 283 NON@is as ctsaks 33-35 days.
1912, Tucson B, g. IV...| Aug. 14-31..... Sept clefessecs 127 Sept. 2-8...... 26-36 days.
ROU CHICA LO Gai Lasceviss| ses aio caveeecs. JUTE 1-20 ons cc s|’ cccesacencsnee'e NONGS scss.000s8 25-36 days.
1911, Chicago g. Il....06] socces os\salbiciele's Sept. 1-10.....] sscsccccccce .--| Sept. 1-10..... 25-30 days
TOUS Chicago e. Le. caa) scwicsiceccciene sss JULY L012. vee) Geese asc siaisieia | INOM Clava e-exw e's .aysis 23-38 days.
1912, Chicago g. 1V.....] .2.0- eoveesecee Sept 4-20 vaisisa|| esleceweiseciee ars Sept. 20-22....| 34-36 days.

Early in September all were in hibernation and remained in the ground during
the winter. On the other hand, at the Chicago Station, the original wild parents
were allowed to breed as a group-culture, and gave generation I in 30 days.
These adults bred as a group-culture and produced generation II in 33 days,
which now hibernated during the winter from September until May, when they
reproduced and gave generation IV in 35 days: for the above data, see Table 2.

The animals for experiment were reared upon potato plants in cages of uni-
form size (6 by 6 by 6 feet), with sides of wire-netting, 16 meshes to the inch.
These cages were furnished with wooden bottoms (6 by 6 by 3 feet), which were
filled with a mixture of equal parts of adobe* and sand. This mixture proved to

1 At Station A, where this soil was obtained, the adobe consisted of a clay loam,
which constituted the soil-mass of the river flood-plain. This soil was about 8 to 9
meters deep and rested on sand and gravel. Livingston (1910) found it to have a
water-holding power of about 18 per cent of its dry weight. The sand used in all
experiments was obtained from an arroyo near at hand and had a water-holding
power of about 39 per cent of its dry weight.

346 RELATION OF WATER TO THE BEHAVIOR OF

furnish favorable conditions for plant growth as well as pupation and hiberna-
tion activities.

The condition of the experiment required that a certain routine be repeated
each time, and some of the most ordinary methods follow. The rates of evapora-
tion were obtained with the Livingston atmometers, which were cut down to a
cone of 50 mm. in length to avoid an error introduced by having shellacked
bases. These were standardized on the rotating machine in the Genetics Labora-
tory at Chicago, and showed after standardization a maximum range of 3 per
cent from the normal. The dry weights of the insects were obtained as follows:
first by killing them in potassium cyanide, and desiccating them at a constant
temperature in a vacuum over concentrated sulphuric acid until the dry weights
became approximately constant. The soil samples when collected were placed
in glass-stoppered weighing-bottles and carried to the laboratory, where they
were weighed and dried at a constant temperature of 100° C. The tropic reac-
tions were tested in the constant-temperature room (18° to 20° C.) and the
beetles were exposed in wire-netting tubes (30 cm. long and 5 cm. in diameter).
All geotropic reactions were tested in the dark, and if the animals crawled to
the top of the tube when held in a vertical position they were considered positive,
and if they moved to the bottom of the tube, negative. The phototropic reac-
tions were tested with an ordinary 32 c. p. electric lamp in a constant-tempera-
ture room. If the organisms crawled toward the direct rays of ight when the
tube was in a horizontal plane they were recorded as positive and if they moved
away from the source of light as negative.

ROLE OF WATER IN THE REPRODUCTIVE ACTIVITY.

A striking fact that one observes in desert biology is that a remarkable degree
of coincidence is shown between the rainy season and the reproductive period
of the animals native to such a region. Corresponding periods of inactivity for
such organisms occur during the dry season. In studying this problem, 'Tower
(1906) finds this is true for most of the species of Leptinotarsa distributed
over the American deserts and similar observations were made by Semper
(1881) for several desert forms.

For many years Tower has introduced chrysomelid beetles into desert com-
plexes of Arizona from a wide range of habitats, and the majority of these
experiments, which were placed under my care, showed that food, enemies, and
the like were not the determining factors in the survival of such organisms, but
that in most instances the survival was successful if the proper complex for the
reproductive activity was attained.

Frequent observations at Tucson indicated that the optimum breeding
activity of the potato beetle was coincident with the highest water-content of the
medium, since periods of egg-laying were exactly concurrent with those of rain
and with the low rates of evaporation. Therefore, it was important to determine
experimentally what relations existed between reproductive behavior and changes
of water-content within the medium surrounding these animals.

The literature of the subject contains much data in regard to the effects of
temperature upon the reproductive activity, but almost none upon the relation
of water to reproduction. In reference to the genus Leptinotarsa, Tower (1906)
states:

THe Potato BEETLE IN A DESERT 347

* Tn both tropical and temperate latitudes, the germ-cells do not develop nor
reproduction take place until the conditions of temperature and moisture are
favorable. .... Likewise, in the northern United States and Canada, decemli-
neata may emerge from the ground in April, but the germ-cells do not begin to
grow until the coming of the warm moist days in May or possibly June.”

Kammer’s (1907) experiments show that Salamandra (maculosa and atra)
can be induced in varying ways to lay their eggs, depending in part upon the
moisture relation. Jacobs (1909) states for the rotifer Philodina rosela:

“The period of maximum egg-production had been preceded by a period of
desiccation and furthermore, that each desiccation for any length of time has
been followed by an increase in the reproductive activity.”

Hennings (1907), working on the bark beetle Tomicus typographus Linn.,
finds that the amount of water present acted as a regulatory factor for such
activities. The results of these investigators show that egg-production may be
modified through changed water-relations.

At Tucson Station A, comparative study of the environmental records indi-
cated that when the atmosphere had a high water-content, and when the
evaporation rates were low, then egg-laying took place most frequently. This
was self-evident, for during the breeding of four generations of the stock at this
locality egg-laying occurred during the following periods: July 7 to 19, August
4 to 22, 1911; June 4 to 15, and July 15 to 29, 1912, which were exactly coinci-
dent with the maximum rainy periods at this station. At Tucson Station B the
results were similar to those of Station A, since the periods of oviposition were
as follows: July 17 to 23, September 3 to 7, 1911; June 8 to 20 and July 24 to
August 12, 1912, which coincided with high humidities and low rates of
evaporation. At the Chicago station, however, the evaporation rates were lower
and the egg-laying was controlled by other factors. For the desert complex
these results indicated that the optimum for egg-laying was reached when the
organism was subjected to a moist medium.

Since these conclusions were only probable, it was advisable that they be sub-
stantiated by further experiment. ‘Therefore, it was necessary to produce
artificial differences in the moisture-content of the medium, and observe its
effect upon beetles during hibernation and after emergence.

For the purpose of these experiments, 120 beetles (Tucson A, g. II) were
removed from hibernation at 8 p. m. June 19 and were placed in ground-glass
stoppered weighing-bottles, so that no moisture could enter. They were removed
immediately to the constant-temperature room of the Desert Laboratory, where
reactions were tested and all responded positively to light and negatively to
gravity. At the same time a sample of the soil surrounding the beetles was
taken and found to contain 11.3 per cent of water by weight. The animals were
now divided into two lots of 60 adults each (30 of each sex), which were found
to weigh 10.007 grams and 9.845 grams, respectively. The first batch was sub-
jected to differences in soil-moisture and its effect upon egg-production observed.
In the second case the effect of changing evaporation-rates upon oviposition was
also observed.

348 RELATION OF WATER TO THE BEHAVIOR OF

EXPERIMENTS WITH SOIL MOISTURE.

It was important to determine the effect of a varying soil-moisture upon
oviposition in these organisms during hibernation. Tubes used in experiments
upon this subject were 30 cm. long and 15 cm. in diameter, and made of wire
netting surrounded by several layers of tinfoil to prevent the egress and ingress
of moisture. Three of these tubes were filled with a mixture consisting of equal
parts of sand and adobe, and then sunk in a large box of sand, so that only the
tops were exposed. The sand in the box was kept damp by means of self-
watering automatic soil-cups, which were devised by Hawkins (1910), the
purpose of this wet sand being to keep the organisms within the tubes at a
uniform temperature, a result attained through rapid evaporation of water-
vapor from the surface of the soil.

The desired differences in soil-moisture were produced in the above tubes in
the following manner: In one tube were placed two porous soil-cups, which
gave the soil a high water-content; in the second one, however, a small porous
soil-cup was placed, which kept the soil within at a lower moisture than in the
former ; and in the third, no soil-cup was employed, thus keeping the soil dry.
It was thus possible to obtain differences in soil moisture with other conditions
approximately uniform. But to make certain that the above apparatus produced
the desired results, determinations of soil-moisture within these tubes were
made every second day throughout the experiment. These data are tabulated
in Table 3, which shows that the moist soil contained 15.8 per cent moisture,
the medium moist soil 8.8 per cent moisture, and the dry soil 1.9 per cent
moisture. Thermometers were placed in these tubes at a depth of 15 em. and
readings were made at 5 and 9 a. m. and at 1, 5, and 9 p.m. When tabulated,
these soil temperatures throughout the test indicated a close agreement for all
experimental tubes.

TABLE 3.

Tube 2. Medium

imotek boil. Tube 3. Dry soil.

Soil samples obtained. Tube l. Moist soil.

Per cent. Per cent. Per cent.
15.9 8.9

UNG Zl ee stays see
ARG 4sig Wernnias ociano : 9.2
June 25....02s00008- : 8.4
June 27 : 8.7

Average...... 5. 8.8

The 60 beetles of batch 1 were now divided into three groups, and when
tested in the constant-temperature chamber were found to react positively to
light and negatively to gravity. Each group was now weighed, group A weigh-
ing 3.341 grams, group B, 3.329 grams, and group C, 3.337 grams, respectively.
Each group was next buried on June 19 at a depth of 15 cm. in each of the three
experimental tubes as indicated, members of A being buried in a moist tube,
those of B in one less moist, and those of group C ina dry tube. These animals
remained as buried until June 27, 6 p. m., when their weights were again tested
in the constant-temperature room, and group A was found to weigh 3.213 grams,
group B 2.962 grams, and group C 2.107 grams, respectively.

Tue Potato BEETLE IN A DESERT 349

Thus it was discovered that the beetles of group A from the moist soil showed
a loss of only 0.128 gram, while their reactions were, as before, positive to light
and negative to gravity. The beetles of group B, however, from the medium
moist soil, showed a much greater loss in weight (0.367 gram), although their
responses were unchanged, except in the case of 3 which were positive to gravity.
The beetles of group C from the dry soil indicated the greatest decrease in
weight (1.123 grams), and showed a reversal in their behavior.

After this test the beetles were put into separate cages out-of-doors and
allowed to breed under natural conditions. A comparison of the rates of
evaporation, obtained with Livingston atmometers when placed within these
cages, indicated that the environment was uniform. When the activities of
these insects were closely observed, the following results were obtained: Those
beetles from the wet soil, whose reactions as previously tested, were still positive
to light and negative to gravity, moved immediately upward on the potato
plants, and began feeding on the uppermost leaves. This indicated that their
activities were normal, and on June 30 eggs were laid. On the other hand,
those animals from the medium-wet soil also fed on these plants, but no eggs
were laid until July 4. This showed that oviposition was postponed 4 days,
but that the dry-soil beetles, whose responses were now reversed, were negative
to light and positive to gravity. They immediately burrowed into the ground
and remained there until the arrival of the summer rains, July 13, when they
emerged and laid eggs on July 15. In this case oviposition was delayed 15 days.
An analysis of these results follows:

These experiments showed that differences in soil-moisture produced changes
in the water-content of these animals as well as modified their behavior. Since
the egg-production was changed, we must conclude that beetles emerging from
soils of high moisture-content lay their eggs sooner than those issuing from dry
soils. The soil no doubt has played an important réle in the economy of desert
organisms, which are known to respond accurately to environmental changes
such as we have described; otherwise many forms would have ceased to exist
where they are now widely distributed in desert regions.

EXPERIMENTS WITH EVAPORATION RATES.

The second batch of beetles was used to determine the effect of differences
in rates of evaporation upon insects just emerged from hibernation. The
apparatus for this experiment consisted of three uniform bell-jars placed over
pots of potato plants. Each pot was sunk into adobe soil in the bottom of a
vivarium, which was an open inclosure covered with wire netting. One of the
bell-jars was provided with 8 atmometers, which, through the evaporation of
water-vapor from their surfaces, produced both a high relative humidity and a
low rate of evaporation. The second jar was furnished with 2 atmometers, and
the evaporation-rate was greater in this jar than in the first; but the third was
kept dry, for, since no water or atmometer whatsoever was used, a high rate of
evaporation was secured. The food-plants in this test were kept in a normal
healthy condition by the use of automatic soil-watering cups placed in the
earth near the bottom of the pots. A few preliminary experiments demon-
strated that the dry bell-jar in direct sunshine would become several degrees
warmer than the more moist; consequently a shade was so placed as to give

350 RELATION OF WATER TO THE BEHAVIOR OF

closer agreement in temperature readings. A small strip of wire-netting was
then fastened around the base of each bell-jar to afford a free circulation of air.

The environmental conditions produced artificially within each bell-jar were
measured in the following manner: Thermometers were suspended in each jar
and temperature readings were taken five times daily at 5 and 9 a. m., 1, 5, and
9 p. m.; they show a close agreement of the three jars. The evaporation-rate
was obtained by means of a single atmometer placed in each jar, and the cubic
centimeters evaporated by this instrument were recorded twice each day at 8 a.m.
and 8 p.m. In averaging the different rates, it was found that the moist jar
showed an evaporation rate of 14.5 c. c. daily, the medium moist 20.7 c. c., and
the dry 25.0 c.c., respectively. The results show that the air temperatures
within each jar were approximately uniform during progress of the experiment,
and furthermore that the anticipated differences in the rates of evaporation were
produced in this manner. Thus the environmental conditions for this test were
experimentally attained.

Sixty beetles of batch 2 were now divided into three groups of 20 each, and
on June 20 were distributed to the jars mentioned above. In the jar with a low
rate of evaporation the beetles reacted normally in feeding upon the potato
plants, and laid eggs on the third day, June 23, but in the jar with the medium
evaporation-rate, the animals, though resting upon the plant leaves, laid no
eggs for 9 days, or until June 29. In the third jar, with a high rate of evapora-
tion, which produced the greatest degree of desiccation, they stayed upon the
potato vines for 5 days or until June 25, when they entered the ground and
there remained until the summer rains began July 11; they emerged, however,
from the soil on July 13, and oviposition occurred within 3 days.

These results showed that egg-production was modified by differences in the
evaporating power of the air surrounding these animals, and that a low rate of
evaporation, coincident with a high water-content, encouraged oviposition, but
that a high rate of evaporation, which reduced their water-content, retarded
reproduction. So with a high rate of evaporation the beetles were desiccated ;
their tropisms were reversed and they entered the soil, where they remained
until their moisture-content was sufficiently increased; they absorbed water
until their reactions became normal, when emergence resulted.

It was shown clearly that reproductive activity occurred during a period of
high water-content in the surrounding medium, whether atmosphere or soil,
and that desiccation, by reversing the animal’s tropisms, inhibited and post-
poned reproductive reactions of the L. decemlineata, which is a typical grassland
organism. This demonstrated that the introduced stock had adjusted itself to
the complex of desert conditions and reacted in the same manner as did the
indigenous organisms of the surrounding region. Accordingly, in the majority
of species, we should expect reproduction to coincide with the season of high
water-content and a dormant period to follow the dry season, regardless of any
discovered structural adaptations.

ROLE OF WATER IN THE PRESERVATION OF LIFE.

In the desert it was found that hibernating insects could continue life during
long dry seasons of one or more years; therefore, experiments were undertaken
to answer the following questions: How was such vitality preserved? Was this

Tue Porato BEETLE IN A DESERT 351

relation due to a reduction of normal physiological activities through desicca-
tion? If so, what relation exists between such organisms and changes in the
physical composition and especially the moisture-content of the medium sur-
rounding them? For these tests, animals of different physiological activities,
induced by differences in humidity, were buried for certain periods of time in
soils of varying degrees of moisture and texture. The criteria used in deter-
mining the power of resistance were the number of individuals surviving in
the test at the end of a given period of time, and the differences in activities of
the insects produced through desiccation, as compared to a similar set in which
the behavior was normal. The capacity of these animals to resist was tested,
and beetles were placed in wire-netting tubes (50 cm. long by 10 cm. in diam-
eter) which permitted a free circulation of air and moisture. The tubes con-
taining the insects were buried upright, so that the base of each was 60 cm. deep
in the soil. The plots were 10 meters apart, in the open, at Tucson Station A.
Earth was removed from each plot so as to leave two holes 6 meters square by
1 meter deep, and each cavity was further divided into equal parts by a partition
of red-wood boards 1 inch thick ; one side was filled in with sand, the other with
adobe. One of these plots was exposed under natural conditions in the open,
while the other was covered with a roof, which extended on each side 1 meter
beyond the limits of the plot. This roof was raised 1.5 meters above the ground
in order to give a free circulation of air and to keep the soil dry underneath.
Water from rains was collected in ditches which conveyed it beyond the plot.
The plot in the open was designated Plot A, and that under roof as Plot B.
The soils in both plots were kept moist by adding water by means of a garden
hose until October 20, but after this date they were exposed to the conditions
of the winter of 1911-12 at Tucson.

The first set of experiments concerned only beetles of the summer generation
that were emerging from the pupa state. Such insects do not normally hiber-
nate, but may be caused to do so through adverse conditions such as those which
cause desiccation. It should be noticed that in one instance the animals were
buried with all activities normal; in the other, they were first induced to
hibernate in cages in the vivarium, and they were sifted out in the soil; in
either case they were finally buried under the conditions described above.

In the former test in which the beetles were buried with all their activities
normal, 400 emerging individuals (Tucson A, g. I) were collected on August
12; 50 of these were then placed into each of the 8 wire-netting tubes ; 4 of these
tubes were filled with sand and 4 with adobe soil; the insects were placed at
corresponding levels in each of the 8 tubes; 2 of these containing sand were
buried in the open plot and 2 under the shelter, while the 4 tubes with adobe soil
were sunk in the adobe sections of the plots, 2 in each. These were left unmo-
lested until May 1, when one tube under each set of conditions was examined
but no living beetles were found. On October 1, the remaining 4 tubes were
inspected with the same results; there were no living organisms found. These
results showed that no beetles of the summer generation with their activities
normal hibernated successfully when buried under the conditions of this experi-
ment. These observations are tabulated in Table 4.

852 RELATION OF WATER TO THE BEHAVIOR OF

In the latter test, however, the insects were first induced to hibernate in
cages in the vivarium, and were then immediately sifted out of the soil, to be
finally buried in Plots A and B. The following methods were used in this test:
During the period of August 13 to 20, emerging adults to the number of 1,613
(Tucson A, g. 1) were collected and placed in pedigree cages under adverse con-
ditions within the vivarium. These conditions were produced by having their
food reduced to sliced potato tubers and by adding just enough water to keep
the soil slightly moist, so that the beetles were partially desiccated. A census
taken September 10 showed that 1,209 insects had successfully hibernated in

TABLE 4.—Census of counts on covered plot and open plot.

Covered plot. Open plot.

Conditions of the experiment. Adobe. Sand. Adobe. Sand.

A. Beetles of summer generation:

1. With activities normal when buried
on August 12. On May 1 the fol-
lowing count was made
Another census on Oct. 1 showed..

2. Others were desiccated and buried on
Sept. 10. On May 1 the following

count was made
Another census on Oct. 1 showed..

B. Beetles of winter generation:

1. Witb activities normal when buried
on Sept. 10. On May 1 the fol-
lowing count was made..

Another census on Oct. 1 ‘showed.

2. Others were desiccated and buried on
Oct. 2. On tay 1 the pe oonies
count was made.

Another census on Océ; a ‘showed.

3. Others were hibernated and buried on
Oct. 7. On May 1 the ponow ine
count was made..

Another census on Oct. y ‘showed..

these cages, and from this result, it was discovered that their vitality was greatly
diminished, for 6% per cent of them were killed by these conditions. Of the
survivors, 400 were divided into 8 groups of 50 individuals each, which were
placed in tubes buried beside the 8 which were described in the former test. All
were left unmolested during the winter and until May 1, when 4 tubes from
each plot were examined. Tubes from the covered plot showed that those in
sand contained no life; 2 from adobe contained 54 living beetles; while 4 were
alive in the sand from the covered plot; the adobe portion of this harbored 46
living insects. On October 1 the remaining 4 tubes were also examined ; those
in adobe soil under shelter contained 12 living beetles, but all were dead in the
sand and there were no living animals in either part of the open plot. These
experiments proved that beetles of the summer generation, which normally

THE Porato BEETLE IN A DESERT 353

breed and produce a hibernating winter generation, may be buried after having
been induced to enter the ground through desiccation; furthermore, that the
animals lived many months when buried under these conditions, but that the
death-rate was greater in the sand, and the majority in the open plot succumbed.
These data are also given in Table 4.

On the other hand, the second set of experiments concerned beetles of the
winter generation which had just emerged from the pupa state. This problem
was considered from three aspects: (1) Some animals were buried with all their
activities normal; (2) others were induced to hibernate through partial desicca-
tion produced through adverse conditions, and were then buried; (3) many
were allowed to hibernate normally before they were finally buried in the two
plots.

For the first test in which the animals were buried with all their activities
normal, 400 emerging adults (Tucson A, g. II) were collected on September 10 ;
they were placed within the sand and adobe portions of the two plots. During
the winter, and until May 1, they were left unmolested, when tubes from each
plot were examined and no living individuals were discovered. On October 1
the remaining tubes were exhumed, but no live animals were found. These
results showed that, when beetles of the winter generation, which normally -
hibernate, were buried with all their activities normal, hibernation was unsuc-
cessful and all the animals succumbed (Table 4).

In the second test, where beetles were induced to hibernate through desicca-
tion, 1,000 emerging adults (Tucson A, g. IL) were collected on September 11,
and were placed under adverse conditions in pedigree cages in the vivarium,
where their food was sliced potato, as in a previous test. On October 2, hiber-
nating adults to the number of 692 were sifted from the soil, and 308 dead ones
were gathered from its surface ; 400 of the living insects were then divided into
8 groups, and were buried within the soils of the two plots, in order to afford
the opportunity of winter hibernation. On May 1 these tubes were examined
for living beetles ; the tube from sand under the covered plot contained no living
adults, while in the one from adobe earth were found 48 living adults ; also those
in sand from the open plot contained only 26 living individuals, while 45 beetles
were removed from the tubes in adobe. In a similar manner, on October 1, the
remaining 4 tubes were removed. In the adobe soil tube, under the shelter,
were found 39 animals, but no individuals hibernated successfully in sand;
moreover, tubes from the open plot harbored no life. The results indicate that
induced hibernation was effected in the winter generation through desiccation,
which increased the resistance of these animals by decreasing their normal
activities. The only insects alive at the end of the experiment were found in
adobe under the covered plot, which proved that potato beetles, when hiber-
nating in adobe, possessed a greater resistance to desiccation than when buried
in sand (Table 4).

In the last test, insects were permitted to hibernate normally, then buried in
Plots A and B. This was a control for former tests, since it showed that no
error was introduced through handling or digging up the animals. For this
test, 1,000 emerging adults (Tucson A, g. II) were collected on September 13;
they were placed in a large out-of-door cage that was provided with potato
plants, and other environmental conditions were apparently normal. After
consuming much food, these animals were in hibernation by October 7; then,

24

354 RELATION OF WATER TO THE BEHAVIOR OF

400 of these were sifted from the soil and buried in the adobe and sand portions
of the two plots, after having been placed in tubes as in previous tests. On
May 1, when 4 tubes from these plots were examined, it was found that the tube
from adobe in the covered shelter showed 49 living beetles, while the one from
sand contained only 4; on the other hand, the tube from the adobe portion of
the open plot was found to have 47 living insects, and those from sand 39. On
October 1, when the remaining 4 tubes were removed, those in adobe from the
sheltered plot contained 46 live animals, but those in the sand none; those from
the open plot contained no individuals which had hibernated successfully. This
natural type exhibited the greatest resistance because of the large number of
survivals, and it also appeared that adobe was more favorable to the main-
tenance of life than was sand.

In Table 4 the results are briefly indicated; it is shown there that insects
with all activities normal die when buried, for no beetles were found under any
of these conditions. It appears also that either the summer or winter genera-
tion may be buried and still live, providing the animals were desiccated previous
to burial. It is also shown that a covered plot with adobe soil is a most favor-
able condition for the preservation of life. It is also demonstrated that insects
can be desiccated at any time, when they will burrow into the ground, and may
remain there many months without apparent injury. These tests further show
that the large pores in sand permitted too rapid drying, so that the animals were
desiccated beyond recovery. Livingston (1910) shows that this adobe soil has
a water-holding power twice as great as sand, which agrees with the above results
and explains why these insects continued to live. Lastly, since the adobe soil in
an arid region does contain such a high percentage of moisture, it therefore
is the best medium for the sustentation of desert life.

RELATION OF WATER LOSS IN INSECTS WHEN EXPOSED TO
CHANGES IN THE RELATIVE HUMIDITY OF THE SUR-
ROUNDING MEDIUM AND ITS EFFECT ON THE ACTIVITIES
OF SUCH ORGANISMS.

The relation of water-loss, 7. e., transpiration and respiration from exposed
surfaces, to the behavior of plants and animals has already received some atten-
tion. This is especially true of plants, the water-relations of which have been
studied by Livingston (1906), Lloyd (1912), MacDougal (1912), Renner
(1910, 1911), and other plant physiologists. The results of Livingston (1906)
are of interest in this connection, since they show that there is a close relation
between the daily march of evaporation, as measured by the atmometer, and
transpiration in plants. The following experiments upon insects show that
these animals exhibit a physiological behavior not unlike that of transpiration
in plants, but the results further show that tropisms of insects are modified by
loss of water, which in turn is governed by the evaporating power of the air.
There is wide literature upon perspiration, but it does not bear directly upon
our problem; accordingly we shall consider such researches as have been made
upon transpiration and evaporation and the efficiency of these processes in
modifying behavior.

The results which follow upon the behavior of insects and other desert animals
and upon the relation of evaporation to their behavior and life economy was

THE Potato BEETLE IN A DESERT 355

reported, by the present writer (1911, 1912), and these results have been
substantiated by Shelford (1914 a, b) and his students, Weese (1917), Hamil-
ton (1917), and Chenoweth (1917). The writer’s experiments upon the potato
beetle and other desert animals (1911) showed that “the fundamental activi-
ties of this beetle, as well as those of many desert organisms, are directly con-
ditioned by their water-content or water-balance. The water-content of the
beetle is determined by the evaporating capacity of the air, the leaf-moisture
content of its food plant, soil-moisture, and temperature. Variation in any one
of these factors may influence not only hibernation, but other habits and
reactions.” This work was carried on during the next year (1912), in which I
stated regarding the behavior of desert animals that “the proportion of water
held in the body, or the water-balance, is correlated with various activities, and
the lowering of this balance, or surplus, inhibits several functions or processes,
and is also followed by reversed response to various external agencies which may
exert a stimulatory action.”

Shelford (1913) records that certain spiders, ground-beetles, wasps, milli-
peds, frogs, and salamanders react in consequence of evaporation, and that a
short exposure to evaporation conditions increases sensibility to it. Aside from
this experimental data, Shelford and Deere (1913) established laboratory
methods for determining the reactions of the above animals to evaporation
eradients. My experiments differ from Shelford’s in being made under natural
conditions out-of-doors, while his studies were undertaken in the laboratory.

Hamilton (1917) studied certain soil insects, in the full-grown larval and
adult state, of the family Carabide, and his results tended to show that an
increase in the rate of air-flow did not effect the larvae as much as did an
increase in temperature or a decrease in relative humidity; the adults, more-
over, offered greater resistance to evaporation and temperature. The experi-
ments upon the horned lizard by Weese (1917) demonstrated a clear-cut reac-
tion to the substratum temperature gradient, while the evaporation gradient
was not the limiting factor. On the other hand, Chenoweth (1917) concludes
that the evaporating power of the air is the best index of environmental con-
ditions affecting the white-footed woodland mouse, as well as other land
mammals, and that the mice reacted to evaporation whether it was produced
by movement, dryness, or heat.

EXPERIMENTS UPON EVAPORATION, TRANSPIRATION, AND BEHAVIOR.

Previous experiments upon L. decemlineata show that tropic activities for
light and gravity can be reversed through desiccation, and furthermore, that
normal reactions are restored if the beetles were surrounded by a moist medium.
On the other hand, it seemed important in this connection to perform certain
experiments, in order to determine if these insects in nature react to losses of
water, which might be produced through desiccation by means of the evaporating
power of the air immediately surrounding them. Therefore, it seemed advisable
to devise certain tests which would show the daily march of evaporation and
transpiration when compared with their behavior.

The first experiment was made to determine the relation between the daily
progress of evaporation and transpiration rates of L. decemlineata when exposed
at three different strata, which were produced by an association of potato plants
that completely filled the bottom of a cage, 6 feet square by 4 feet high, and

356 RELATION OF WATER TO THE BEHAVIOR OF

covered with wire-netting. This dense growth produced horizontal zones with
atmospherical moisture, varying from high water-content at the bottom of the
cage to one of low content above the plants in the open.

All beetle exposures and environmental measurements were made every
2 hours for a period of 12 observations at 3 strata within the cage, where insects
and instruments were exposed within wire-netting tubes, 30 cm. long and
5 cm. in diameter. Stratum A was 5 cm. above the ground near the base of the
potato plants, and contained the greatest moisture, thus giving the lowest
evaporation rate; stratum B was 60 cm. above the ground, near the center of
the cage among the plants, and was directly above stratum A, so that it con-
tained less moisture, which gave a medium rate of evaporation; while stratum
C was 90 cm. above ground and 5 cm. above the tops of the plants, and furnished
the driest conditions, with a high evaporation-rate, which was the only exposure
to true desert conditions. Each stratum was directly above the other, and all
exposures were made near the center of the cage. The environmental measure-
ments were obtained as follows: The evaporation rates, by using Livingston
atmometers ; relative humidities from wet and dry bulb readings ; temperatures,
from uniform standard centigrade thermometers.

The environmental measurements were made every 2 hours for a period of
12 observations at the 3 strata within the experimental cage as previously
described and at the beginning of each period a new batch of beetles was
exposed to these conditions for 2 hours. The results are given in table 5.

The beetles used in this experiment (Tucson A, g. II) were collected as soon
as possible after their emergence. Since these newly emerged individuals take
no food until after 24 hours, all collections were made previous to this time, so
that no error might be introduced in consequence of feeding ; moreover, no food
was given them at any time, and no excretion of waste products by the animals
was observed throughout the test. The beetles were placed at once in bell-jars
of uniform size in the constant-temperature room, which stood at 24° C., and
a high but uniform relative humidity was produced by placing wet filter-paper
inside the jars; this kept the air of the jars approximately saturated and the
beetles absorbed moisture until their reactions and physiological states were
uniform, as was proved by tests made later.

The animals were retained in the jars until needed for further experiment.
Three batches of 10 beetles were removed from the constant-temperature room,
and exposed every 2 hours in wire-netting tubes, at the 3 strata within the cage.
Each batch was made up of similar stocks as follows: 4 individuals of 180 adults
which had emerged on July 5 were placed in the constant-temperature room at
8 a.m. July 6; 3 adults of 110 individuals which had emerged on July 6 were
also placed in this chamber on July 7; and 3 animals of 124 adults which had ©
emerged on July 7 were likewise placed in this room at 10 a. m. July 8; while a
batch of 30 beetles which emerged July 8 received the same treatment at 12 p.m.
July 8, and were used during the last 2 hours of the experiment, beginning at
4p.m.on July 10. Thus all the organisms used were of the same culture and
of the same parents; in general they were of the same age, and approximately
of similar states, so the conditions of the test were uniform.

Aside from the environmental records, the following was also determined as
far as the insects were concerned: the total weight in grams of 10 beetles when
exposed, their weight in grams after 2 hours’ exposure, the total grams of dry

THE Potato BEETLE IN A DESERT

357

weight for each batch exposed, the grams of water in the beetles, the total per-
centage of water in the animals, the loss percentage of water in terms of entire

weight, and the loss percentage of water in terms of dry weight (‘Table 5).

Time of observation.

TO} as. Miss

12 noon..

to
0
5B

Gp. MM...

Si p.m. <

10 p. m...

12 p. m..

> Owe ‘awe awe ‘Owr> ‘owe Ow ‘o

: : :

amen

—S

ne A> AW> AWP

Stratum.

Quer AW

Rate of evaporation.

is)

=) _

- =
RW TWH AWN D|WNW OP LRTI ON coor AOR CRN AWM WNN-

Deb Hew NDE CHO OOS Waa HHwW POR ORY NAN ownmn awo®?

TABLE 5.
4G bo o.
. S32 a = S38 S
; | 2) 25 | &s | =F | 28] &
5 || 22) 2/28 | Be | 22
2 |2 | 82 | 38] gs | 2S | 23
Q o we ov 3 es &
8 | & | Fa Fe | £2 | sg] sa
o » “Oo =| Q, ont me)
a = Se So ax 3°09 Ss
He, ® O65 on °° of” om
< [oa] Ba B 4 B B
°C. |p. ct.| gms. gms gms gms. gms.
26.8! 36 |1.2957}1.2700|0.0257|0.239 |1.0567
26.8) 33 |1.2879/1.2574/0.0305|0.235 |1.0529
27.3) 30 |1.2367|1.2028/0.0339/0.229 |1.0077
27.9| 35 |1.2435/1.2150|0.0285/0.230 {1.0135
33.2) 23 |1.2860/1.2405|0.0455/0.275 |1.0105
33.9} 22 |1.2400/1.1585/0.0815/0.226 |1.0135
30.8] 35 |1.1840/1.1496/0.0344|0.223 |0.9610
36.2; 19 |1.1740;1.1196/0.0544,0.213 |0.9610
36.2} 15 |1.1870)1.0500/0.1370|0.218 |0.9690
33.3] 30 |1.2090/1.1320/0.0770|0.232 |0.9770
40.2} 15 |1.2750)1.1590/0.1160/0.272 }1.0030
40.0] 12 |1.2140)1.0405/0.1735/0.236 |0.9780
33.9] 28 |1.2415}1.1610)0.0800/0.229 |1.0125
40.5] 13 |1.1005|0.9805/0.1200|0.209 |0.8915
40.0} 11 |1.2540/0.9800/0.2740/0.232 |1.0215
28.3) 33 |1.2565|1.2015/0.0550/0.215 |1.0415
37.3] 15 |1.2230/1.1185/0.1045/0.213 |1.0100
37.1] 12 |1.1965/1.0550/0.1415/0.217 |0.9795
28.4) 35 11.2030/1.1815/0.0215|0.210 |0.9930
34.0} 19 |1.2380/1.1885/0.0495|0.219 11.0190
33.4] 14 |1.2780)1.2110\0.0670/0.234 {1.0440
25.4] 43 |1.2080/1.1845/0.0235|0.213 |0.9945
30.6] 24 |1.1580)1.1295/0.0285/0.214 |0.9435
30.0} 17 |1.2565|1.2160/0.0405|0.239 |1.0175
25.0] 44 |1.2660/1.2375|0.0285/0.228 |1.0380
29.7| 27 |1.2230/1.1900/0.0330/0.223 |1.0000
29.0} 23 |1.2055/1.1606|0.0449|/0.220 |0.9855
24.1) 47 |1.1727|)1.1420/0.0307 |0.224 10.9487
28.0; 31 |1.1693/1.1380/0.0313/0.222 |0.9473
27.5) 27 |1.1384)1.0489/0.0489/0.213 |0.9254
24.3| 45 |1.1422)1.1122/0.0300/0.224 |0.9182
27.1) 28 |1.2815/1.2435/0.0380/0.251 {1.0305
27.2) 25 |1.1390)1.0990|0.0400/0.225 |0.9140
22.3) 56 |1.4385/1.3975|0.0410|0.301 |1.1375
25.2] 33 |1.4550/1.4010/0.0540/0.312 |1.1430
25.2) 27 |1.5375/1.4795|0.0580|0.328 |1.2095

Total H,O in the

beetle

Ss.

—

—
mal

ily?

mow DOP oo 3 ;
Stora hae Soe. Loss H,0 of entire

Ne

Awnrl
ee
or)

—e
Ron
aS
ts

BRO PHO TOWW PWD WHWHNH APL

weight.

QWoOmns
Owmww os

One
roe

Ss NANO KH On
So FOTO PDD

.82

wr
=

me CO
— orc

oow
vol nemor)

Loss H,O in terms of
their dry weight.

358 RELATION OF WATER TO THE BEHAVIOR OF

REE CHR Re een ae
ROR ees a aa fe my

Transpiration Rate Curves on
Basis of Entire Weight
ze
~
4
Air Temperature Curves
in Degrees C.

g 2.0%) | 5
- CHAE AT a

ae" aN IPA n
Fran ZAI eNO
ge LTR ATIVAN TT" Es
£3 at VAIN, 8
i CeanaNS7=02 GSBBERSUERE :

20% pl SS HH jor

CEN et
Bene Geeee Rae eeee
fe NR

| |
MEY TTT ey

Curves of Evaporation Rate
S
ae

Relative Humidity Curves

A EL BNEBBIS
nb AZLLCN ENO aT Te
CeCe PSN th eee
eet CTP NGI NS Ena mein
Howly-S 72 2s 6 SI 2 oda a ae
Units AM. P.M. P.M. AM. A.M. P.M. A.M. |

Fig. 1.—Curves showing relation between daily progress of evaporation and
transpiration rates of beetles when exposed to different strata produced by an
association of potato plants. Consult table 5 for above data.

Stratum A Stratum B
Curve 1= Rate of Curve 1= Transpiration Rate or
Water Loss Rate of Water Loss
Curve 2=Rate of — Curve 2= Evaporation Rate
Evaporation Curve 3= Air Temperature
Curve 3= Air Temp.

ERRRRARERAD EECCREESE
REEREA eee CASLECEE CEU
PRR PACT lbh
REP AV ERREER a 7 erat Tl eae
et sliver N Raat Tew

Hob gl im wt A baal!

Units

J
>

aca Ne slat SEER IL
jar ela BaaeS Cer fal
swe sos we 2 4 OM? 274 26.781

A.M. P.M. Hee P.M. P.M

Fic, 2.—Results recorded in table 5 reduced to unity and curves plotted in
order to draw a closer comparison than is given in figure 1. The same conclusions
are self-evident.

THE Porato BEETLE IN A DESERT 359

Figure 1 shows the plotted results for the data of this experiment. The broad,
heavy lines give the results for stratum A, the broken line, the results at stratum
B, and the narrow line those for stratum C. The abscisse represent the 2-hour
time intervals, and each unit along the ordinate represents for the evaporation
curves, 2.5 ¢.c.; for the transpiration curves in terms of entire weight, 3 per
cent; for the transpiration curves in terms of dry weight, 13.5 per cent; for the
relative humidity curves, 5 per cent; and for the temperature curves 2.5° C.
These graphs are interesting in that they show a close agreement between the
evaporation-rate and transpiration curve for each stratum. Since the humidity
and temperature curves coincide closely for the two upper strata, and the
evaporation and transpiration curves for these strata vary in a similar direction,
it appears that the rate of loss of water from the animals when exposed to the
atmosphere agrees closely with the evaporation rates; 1. e., the transpiration
curves of these organisms, as Livingston (1906) found with plants, are largely
controlled by the evaporating power of the air.

TABLE 6.—Summary of rate of evaporation in each stratum combined with loss of
water from the beetle.

Location. Evaporation. Transpiration.

Stratum. 3 acs Loss per cent H,O. Ratio.

Figure 2 shows the water-loss in percentage, the evaporation-rates, and the
air-temperatures, all reduced to unity. The broad, unbroken line represents
the rate of water-loss in each case; the narrow, unbroken line, the evaporation
rate for each stratum; and the broken line, the air-temperatures for each
stratum. In making comparisons broadly, the air-temperatures agree in being
represented by nearly straight lines, so that they were negligible; but the
evaporation curves and curves of water-loss differ for each stratum, yet are
similar when compared. At stratum A, the evaporation curve rises more
rapidly and higher than the curve of water-loss, and the drop in the evaporation
curve is faster than in the curve of water-loss. At stratum B, the curves of
evaporation and of water-loss parallel each other until 6 p. m. when the evapora-
tion curve drops more suddenly. At stratum C the increased air-movement is
an added factor in the environmental complex, so that both the water-loss and
evaporation rates rise much higher, although the temperature curves remain
the same. The curve of water-loss at stratum C rises more rapidly and higher
than the evaporation curves. The latter drops sooner than the curve for
evaporation. This appears to be due to the fact that the beetles are more
sensitive to the environmental fluctuations than the porous-cup atmometer, so
that difference might account for the lagging effect.

These differences in the rate of evaporation in the three strata and the water-
losses are given in Table 6. This table shows that approximately 1 c. c. loss
from the cup is equal to 1 per cent loss of water from the beetles exposed.

360 RELATION OF WATER TO THE BEHAVIOR OF

The evaporation rates here shown gave greater differences within this experi-
mental cage than were obtained by Fuller (1911) for all the plant associations
studied. Shelford (1912) uses Fuller’s data with tables and compares them
with conditions in certain animals, stating that distribution and succession of
the animals is clearly correlated with evaporating power of air. By a further
comparison with the description of stations, Shelford shows that the evaporating
power of the air may be taken in this case as an index of materials, abode,
and the like. Since the evaporation ratios existing inside of this cage
filled with potato plants are greater than those obtained by Fuller for the
stations such as Shelford used, it appeared that L. decemlineata reared in such

TABLE 7,
Environmental conditions Leptinotarsa decemlineata subjected to desert conditions.
determined.
~ ' icone o
S sles os els |./ 3 - & (|b (se lo |s
n ~ ~
gsios|ej2 13) & 2 2 |2~ |” |e |
od mina oO lq =e +7 : — es =3 . on Ba PA
Time. ze ad gle |a| #8 SH Re s a i cs =, ee General Remarks.
Fare SiS .je| te | Ewe | Se |p ew Pe woe! on
OSise| 7 |sb) 2] 33 ae BO [OSLER S| Oe o>
B%/00| & |DF! 6 ca ak oF |SSEIOSBI Sa 55
Oo |i <m 4 <3} ° jen) re) joo) A |h
c.c.|c.c.|° C.| % |No.| gms. gms. gms. |%H,0|\%H.O| No.| %
10 a. m. 0.0} 0.0/30.2) 52 | 25 | 3.4650 | 0.0000 | 0.0000 | 00.00) 00.00) 15 60
lla. m. Dal Soles | 549 2B | Pees ell isicreanee NODOOEIM ISHCNedl teeer. 23 92
1 p. m. 6.21S2 1/3450) B2 2G"l aeiecc | etees Soc noses receccr 23 92
2p. m. 2.7| 2.7/84.2| 33 | 25 | 3.8270 1380 0345 | 15.03} 3.76) 15 60
3 p.m. S850 85.40/32) 26. cies || careeeres|l sielveciel'| lect were. |e cores 21 84
Bye may 118.0) S107 7 Re 6 ly. acts uence | oeeee M caeenl See 21 | 84
5 p. m. Ss2| 0322/8066) GO| 2D} case |iveecinte |) eepecs. Neneccrlllsemeos 25 | 100
6 p.m. 4.3) 4.3/34.2| 81 | 25 | 3.2365 0905 0226 9.86; 2.47) 25 | 100
7 p.m. QB Qe Si B2.0) 0: | 26) ||\esccisoucrs. |, vesisies. | ewiacau lew ete licieiese 25 | 100
10 p. m. 6.2) 1.7|28.3| 46 | 25 | 3.1870 0495 0124 5.39) 1.35] 25 | 100
6a.m. 7.0| 0.9/23.7) 77 | 25 | 3.1490 0380 0050 4.14 52| 24 96
10 a. m. 4.4] 1.1/83.2) 49 | 25 | 3.0725 0765 0191 8.33} 2.08] 24 96
2p.m. (|14.8] 3.7/22.5| 82 | 25 | 2.9895 0830 0208 9.04} 2.26] 23 92
4 p.m. Bs0| SAO Soa ADO 5 isles saecsye: ills crstorela el, seyareistaien fe crstetael lameetersie 0 0| Very cloudy.
5p.m. | 0.0) 0.0\22.8| 90 | 25 (Beetles increased in weight.) ah 44; Absorbed H,O from
6p.m. | 1.8) 1.8|86.8| 64 | 25 | 3.4280 | .4835 -1168 | 47.22| 11.81) 21 84 the air.
9p. m. 3.0/ 1.0/25.2] 69 | 25 | 3.3940 .0290 -0097 8.16] 1.05] 25 | 100
12 p. m. 4.8] 1.4/23.4) 73 | 25 | 3.8715 -0225 0075 2.45 -82| 25 | 100
3 a.m. 1.7) 0.6/23.5| 70 | 25 | 3.3540 0175 .0058 1.91 -64} 25 | 100
6 a.m. 2.0| 0.7/22.7| 82 | 25 | 3.3295 0245 -0082 2.67 -89} 25 | 100
9 a.m. 1.8} 0.6/28.6) 66 | 25 | 3.2880 - 0415 .0138 4.62} 1.51] 23 92
12 a.m. 6.4) 2.1)31.4) 41 | 25 | 3.1825 -1055 -0352 | 11.49} 3.83] 22 88
8 p.m. 9.7| 3.2/383.6) 42 | 25 | 3.0840 -0985 .0328 | 10.73} 3.58) 21 84) 0.0705 gm. deducted for
6 p. m. 6.7| 2.2/31.2| 43 | 23 | 2.9405 -0730 -0243 8.42} 2.81] 14 61 2 died.
9 p.m: 6.2) 2.1}28.0] 52 | 23 | 2.9035 .0370 0123 4.27| 1.42] 16 70
12 p. m. 3.5) 1.2/26.3) 62 | 23 | 2.8800 0235 .0078 Bell -90| 17 74
6Ga.m. | $.9| 0.7\24.8| 72 | 28 | 2.8985 | .0135 | (Beetlesabsorb HO). 78 Absorbed H,O from
6p. m. |18.4| 1.1|\24.1| 92 | 23 | 3.2695 -8769 0814 | iad a 28 | 100 the air.

a cage has a great range of adaptability. From the base of the potato plants to
just a little above their tops, there existed zones of evaporation of wide extremes.
To illustrate, Table 5 shows that from 2 to 4 p. m. at stratum A the evaporation-
rate was 4.6 c.c. and loss in water-weight of beetles was 7.9 per cent of their
entire weight; at stratum B the evaporation rate was 8.9 c. c. and loss of weight
of animals exposed, 13.46 per cent; and at stratum C the rate was 19.4 c. c. and
loss in weight of the beetles was 26.82 per cent. This shows the evaporation
ratios to be 1.00: 1.93: 4.22, and the transpiration ratios to be 1.0: 1.7: 3.4.
For the whole experiment, the ratios of evaporation were 1.0: 1.7: 3.4, while the
transpiration ratios were 1.0: 1.5: 2.4. In general, these ratios are very similar,
showing that there is a direct relation between the evaporation-rates and trans-
piration percentages, and it answers in part the question already raised: Do

Tue Potato BEETLE IN A DESERT 361

the evaporation-rates, the transpiration curves, and the reaction graphs of these
organisms correspond? The following experiments give us a further affirmative
response by showing that such a correspondence does exist in the potato-beetle
and other insects.

The first experiment was performed out-of-doors at the foot of Tumamoc hill
near the experimental cages at Tucson Station A. The beetles which had
newly emerged from the pupa state were collected at night. They were kept
under saturated bell jars at a constant temperature until morning when they
were placed in wire netting tubes. At 11 a.m. on July 19 they were exposed
to the desert conditions in the open until 6 p. m. on July 21. The following
environmental conditions were determined hourly: the rate of evaporation, the

* Curve 2= Transpiration Rate: Dotted Por-

c
2
2 Ae
B
z ao
=
oy =;
ov fo
BS 3
= jo
3 © 80
n 4
ia =| he
= = Ss
Ou ce
2 o
3 E
= 5
n
i=7
rp
~
Vv
‘o %
ee een aubed a
< |
= GRRE Re EeA Gos ieee g
S99 f a %, 3
eee Ve es RES RS Bee:
: i q
t
oe oO.
5 2
a) a.
Hourly
Unit 1

Fic. 3.—Curves 2 and 3 show the relation of evaporation to Eeeviaton
(water-loss) of beetles when exposed out-of-doors at the foot of Tumamoc hill;
however, Curve 1 shows that the reactions of this insect to light were in general
the reciprocal of the evaporation and transpiration curves.

air temperature, and the relative humidity. During this experiment, the entire
weight of the beetles was also determined, as well as periods when these insects
gave off water to the atmosphere. It is of importance to plant and animal
physiologists to state that these beetles absorbed water directly from the
atmosphere. Aside from these determinations, others were made, which
include the hourly loss in weight of these insects, the observed loss of water in
terms of their dry weight, ne daily loss of water in terms of dry weight, and
the number of the beetles which were positive to light as well as the percentage
positive to light. These results are given in Table 7 and the figures in italics in
Table 7 show ; periods when the beetles absorbed water directly from the air. The
evaporation rates and the transpiration and reaction rates of Leptinotarsa are

plotted in figure 3.

362 RELATION OF WATER TO THE BEHAVIOR OF

By consulting this figure, one can see at a glance that the curves for trans-
piration and evaporation correspond. Moreover, the reciprocal of the reaction
or behavior curve also corresponds to these curves in a similar manner. Thus
in the reaction of the potato beetle, its percentages of positiveness was, broadly
speaking, the reciprocal of the transpiration curve. This seems to show that the
loss of water from the animal, when exposed in the open, determined the reac-
tions of the insect.

TABLE 8.—Results of subjecting other insects to the same environmental conditions
as Leptinotarsa decemlineata.

S fo} on - 2
3| 2 a se [aso | Sb |e |
rey a wo nes a oO a —
Ga) Ay i} a cr Bw > rs
In- 2 | °. as ° o. | So. | s Buss
Time. & Se ea musa (0S cet) | ee, | ses 2a General Remarks.
nets oul ee) St | be | Som) Pew! $8 | o&
S| #8 | Ss | BS | SES] Ses | fa] os
e pen Dy J ne a) oom ao
fo} an oF oF ae one om or
Z & (o) joo ° jee) a Oy
No.! gms. gms. gms. | %H2.O|%H.20| No. | p.ct
10 a. m. 10 | 7.2700 | 0.000 0.0000 0.00 0.00 9 90
a ll a.m. 100) Gaveteiaieie, 1I\| ave teieiece! ||) inistniaiae elajoraicie eee 10 100
= Tips ms) || LOH cease oi a od een sea 1o | 100
ey 2p.m. | 10 | 6.9715 2985 0746 | 11.09 | 2.77 10 100
ss Elpeests BARS LA| eosin |e rear dl Me sates = 10 | 100
8 Asati || 10) eteccerey Meenicwa || welsereaionll: aac oe A 10 100
a Bipes 10) essere |i cawiersiers caeieeNl lh ceo 10 100
— 6 p. m. 10 | 6.7025 2690 0675 10.34 2.59 10 100
‘ eperiis wh OMe 55 lene ace | ceeoecmlline nee a Se 10 | 100
ss 10 p. m. 10 | 6.4970 -2055 .0514 7.90 1.98 0 0
o 6 a.m. 10 | 6.3620 .1350 .0170 5.19 0.65 0 0
10 a.m. 10 | 6.17385 . 1885 .0471 7.26 1.81 0 0 | All dead.
& 10 a. m. 16 | 2.1790 | 0.0000 ; 0.0000 0.00 0.00 0 0
° ll a.m. RG: |) is ietorstssoyd llr telelermtes || ctete/e’e el lf iaieietele 0 0
= Dope “ett g1 Bil |e orate al pein Ih clemea ss ll bseenets 0 0
> 2 p.m. 16 | 1.9900 1890 0473 | 22.16 | 5.54 0 0 | 3 dead; deduct 0.235 gm.
ao Geen XTl onl Gal ee siareroran | ita slererere Sesieise || wesses 0 0
a5 4 p.m. DZ Ueecuctale arateieratend in aisiele 6 itiae aces BAR 0 0
oo 5 p.m. UBi |) core myersiays| siesta apie |Inaveaarete! |) wie'stare F 0 0
Be 5 p.m. | 13 | 1.5715 | .1844| .0461 | 6.21 | 1.55 ° 0 5 dead = 0.4595 gm.
Pa p: mm RS lll eraterasoveval| crete every Il cavateteseretatl “etovare ere .
| 10 p. m. 8 | 1.0545 0575 0144 10.23 2.56 0 0 | 2 dead = 0.2225 gm.
se 6.4. mi; 6 | 0.8030 0290 - 0036 7.30 0.91 0 0
a 10 a. m. 6], wenen Bo lcicecnd li seats en ll Uatetatoers rae ) 0 | All dead.
a] 10 a.m. 8 | 2.9510 | 0.0000 | 0.0000 0.00 0.00 0 0
2 ll a.m. SSF [fare atcretect || notoustcrare || aatsratroremal | attoreaes ; 0 0
2 1lp.m, Bi [eco ll rcsatarinr ll) racine [ues e es vs 0 0
oa 2p. m. 8 | 2.7845 1665 .0416 18.79 4.70 0 0 | 2 dead = 0.7525 gm.
Fee 3 p.m, Cal Meare ecnenes eee sees 5 0 0
29 A Deis: | Aes | Weeccee || Meiers a heteonten Ices es 0 0
oe 5p.m. | 6| 1.9440] .0880] .0220] 14.42 | 3.61 0 0 | 2 dead = 0.6005 gm.
a | 6 p. m. mn ocd hans con locos vlecoee oes 0 0
2 [ ap. mM. 4 | 1.3055 . 0380 -0095 9.84 2.46 0 0
A 10 p. m. 4 } 1.2705 -0350 0044 9.07 1.13 0 0! All dead.
10 a.m. 9 | 5.1725 | 0.0000 | 0.0000 0.00 0.00 5 56
a Ha, mm; soem uilecriancrl le canct: fal Rate 5 66
= 1p.m. Dll ess coreseres.l]avolensvara «| Pioleatatetond| |) muetcietete 5 8 89
2 2p. m. 9 | 4.8263 3462 . 0866 27.64 6.89 4 44
a 3 p.m. Gl iersteereulteaen eat molest Seteree : 4 44
» 4 p.m. ON Cerra Dacia mere rd besccrick 5 56
a 5 p.m. 9 | cease. | elves ieaecome ||P aceon sdisle 4 44
= 6 p. m. 9 | 4.6005 -2258 0565 17.96 4.49 3 383 | 1 dead = 0.4075 gm.
5 7 p.m. Bil eesicrer en!) tentecoteseeal| Pevcistaister|liuesyoretoce aia 0 0
10 p. m. 8 | 4.0340 - 1590 -0398 14.11 3.53 0 0 | All dead.

The second experiment was performed to determine the relation of evapora-
tion to the transpiration and reactions of insects when exposed for several days
under natural conditions. To get a comparison between L. decemlineata and
other insects, a cricket (Gryllus), a beetle (Catalpa lanigera), and two species
of June-bugs (Lachnosterne) were used, since they could be collected in large
numbers. These insects, with the exception of the potato-beetles, were obtained

Tur Potato BEETLE IN A DESERT 363

at night by aid of a light, and were collected as soon as possible after emergence.
All were placed at once in bell-jars in the constant-temperature room. A high
relative humidity was produced as before by placing a wet filter-paper inside
the jars, which permitted the animals, if not already saturated, to absorb water,
‘so that their water-contents would be as uniform as possible, and they would
attain, in this respect, a similar physiological equilibrium. The insects were
retained under these conditions until 10 a. m. the following morning, when they
were exposed in similar cylindrical tubes. The instruments for measuring
environmental conditions were also placed in these tubes, which were suspended
to a wire and placed in the open, so that each tube was inclined toward the north.
The direct rays of the sun were thus permitted to fall upon the tubes at right
angles. Unless otherwise indicated in Table 8, the observations were made
hourly from 11 a. m. July 19 to 6 p. m. July 21, and for the environmental
conditions consult Table 7.

Jt 2 see ee SaaS Sa Seiwa

Curve 1= Evaporation Rate

BRS eee eee eases
PT TTP ATA TTA TY TSA ET

SAL Zs
one Be ee

Curve 2= Air Temperature
w
Oo

REE AH
Pee ether ey
| SARE SASS SARE RRAARE SEA BE!
eo Re ie
2 Sea eee eae
2S a2 a a ene eee eee,
, See SSeS aes eee aa
_ _ Sa eeereen aes
|. SSSR Sees

ee Se La a

Hourly

Unis 2 34S 6 TS O10 il 1d 13 1d 1s 16 17-*18 19-2 DT SG RT OS

Fig. 4.

If one should plot the results given in Table 8, he will find that all

of the

organisms used give a transpiration curve which corresponds with their curves
of evaporation. Catalpa lanigera and the crickets reacted to transpiration in a
manner not unlike the potato beetles, while the Lachnosterne always gave a
negative response, regardless of conditions.

Another experiment upon loss of water and insect activity was made as a
conformatory test, in which the methods and materials used were similar. The
animals consisted of 31 DL. decemlineata (Tucson A, g. III), 10 Catalpa lani-
gera, and 20 Lachnosterne. The latter were collected around an electric light
and then placed in a refrigerator. All instruments and insects were exposed
in the open in large netting spheres and hourly observations were made from
9 p.m. August 9 to 4 p. m. August 11; the complete data are given in Table 9.
The evaporation-rates, the air-temperatures, and the relative humidities are

to

So

<< 5 6
Curve 1= Evaporation Rate

Relative Humidity

Curve 3

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‘6 TIdVL

Tuer Potato BEETLE IN A DESERT 365

shown in figure 4, while the transpiration and reaction curves of Leptinotarsa
decemlineata and Catalpa lanigera are given in figure 5. The upper diagram
contrasts for the potato beetle its transpiration rate with the percentage posi-
tive to light, while the lower half of the cut does the same thing for Catalpa
lanigera. ‘This experiment was similar to the former ones, in that the insects
were subjected to the environmental conditions out-of-doors at the foot of
Tumamoc hill.

For other data and comparisons Table 9 should be consulted; the results
given show that the evaporation curve as measured by the porous-cup atmometer
and the transpiration curves of the insects are similar, as was previously found
to be true. Moreover, the positive reaction curve of the potato beetle was the

55.0% 100%

g ZeReeser Nes Srany' Leptinotarsa decemlineata .
Soe LLLELL UTE ALLAN ee
g eee ee ee e
Foot ALT TT ET TT A TAL TT tt leon 83
E ie
x 17.5% 25% 2
z 5
8 a 2

OA fees pest ecto 0%
er PA oat
2 | 2
5 4
= 6.2% 65%
2 foe
= =
4.2% 40% 8
4 &
5 4
a 2.2%1f-4 15% 'y

. 2 ee ee se 0% S

Fia. 5.

reciprocal of its transpiration curve. In the same way the reaction curve of
C. lanigera was associated with its transpiration curve until 9 a. m., when all
reactions became negative. The Lachnosterne appeared here only with a
negative reaction, regardless of their transpiration curve, which agreed with
the curve of evaporation.

These results prove, in the first instance, that the evaporating power of the
air was the determining factor in the transpiration of these animals, a result
similar to that obtained by Livingston (1906) for plants; secondly, that there
existed from the base to the top of associated plants, in an arid region, an
extreme zonation, in which great differences were found in the evaporating
power of the air, and that this in turn controlled the rate of transpiration ; and
finally, that the evaporating power of the air surrounding the organisms deter-
mined their behavior through transpiration. Moreover, many animal organisms
of the desert exhibited great localization in their distribution and the ruling
feature of the environmental complex, whether it entailed a habitat of trees,
among rocks, or in soils, was that of the moisture-relation.

366 RELATION OF WATER TO THE BEHAVIOR OF

ROLE OF WATER IN HIBERNATION.

It is an established fact (Tower, 1906) that in the second or winter genera-
tion Leptinotarsa decemlineata in its homozygous state always hibernates under
normal conditions, but that desiccation, or cold, or both, might produce hiber-
nation at any time. At Tucson it was also found that whenever the conditions
became adverse enough to produce desiccation, hibernation was produced. Tower
(1906) showed that preparation for hibernation in the winter generation con-
sists largely in the reduction of the watery contents of the body and in an
elimination of all food and other substances from the alimentary canal.

These facts indicated that the loss of water appeared to be produced by two
different mechanisms. One was controlled by an external medium, while the
other was determined by heredity. In the former, water was extracted from
the tissues through desiccation due to conditions in the medium, while in the
latter water was eliminated from the tissues through internal processés under
normal conditions. Tower states:

“ Preparation for hibernation consists in a physiological change in the con-
stitution of the body for the time being and a consequent lowering of the
freezing-point of its tissues in exactly the same way that spores of many plants
and the over-wintering eggs of rotifers prepare for the coming of the unfavor-
able conditions in their environment.”

The following experiments were performed to show how the above results can
be brought about through desiccation. At Tucson this type of hibernation was
quite common, but did not occur in nature at Chicago.

ENTRANCE INTO HIBERNATION.

It is evident that in the potato beetle entrance into hibernation may be
“ induced hibernation,” which occurred whenever the evaporating power of the
air surrounding the insect removed more water by weight in a given time than
was introduced into the organism by food and other agencies. Such desiccation
produced in the course of one or two days depended upon the adversity of the
conditions, thus effecting change in the beetle’s behavior, so that its reactions
were reversed and it burrowed in the soil.

Extensive observations were made at Tucson Station A, where it was dis-
covered that this type of hibernation took place whenever sufficiently desiccating
conditions existed. The evidence of such a reaction in a large population was
determined by comparing the daily environmental readings with counts of the
non-hibernating population, which showed that during the rainy season and as
long as water was added to the soil no entrance in this type was found, but when
water was discontinued desiccation occurred and hibernation resulted. On the
other hand, at Tucson Station B, the “induced hibernation” was always
observed as the prevailing type of behavior, since in this habitat the conditions
were more adverse. Moreover, at this locality, the growth of the food plants was
retarded, since the leaves were tougher and showed less water-content ; desicca-
tion was also much greater, so that the response of the organisms to such
rigorous conditions was sharper than in any other locality under observation.
This clearly demonstrated when a comparison of the daily environmental
records were made with the daily count of beetles, which were found out of the

Tue Potato BEETLE IN A DESERT 367

ground during one month of the rainy season. At Chicago, however, no induced
entrance was discovered, since the conditions were more favorable there for
normal activities, as the daily environmental readings indicate. From these
observations it is evident that a type of hibernation occurred during periods
of low water-content in the surrounding medium; this produced a lowering of
the beetles’ content and induced a set of reactions so that a type of behavior,
potentially hibernation, resulted ; to determine exactly the réle of water-loss in
the observed reactions other experimental tests were performed.

For the purposes of this particular problem, the first test consisted of inducing
estivation by desiccating adults of the summer generation, which do not
normally hibernate. The beetles for this experiment consisted of 259 adults
(Tucson A, g. III) which had been placed in a culture cage filled with potato
plants. They were allowed to feed until July 15, when a few bunches of eggs
were deposited, and at 4 p. m. 200 of these beetles were collected and divided
into two groups of 100 each, regardless of sex. The beetles were weighed,
group A weighing 12.16 grams and group B 11.52 grams, respectively. Group
A was now placed under a bell-jar with calcium chloride and group B under a
similar jar filled with wet filter-paper. The jars with the beetles were placed
side by side in an adobe building under identical conditions, except for differ-
ences in the desiccating capacity of the medium within the bell-jars. Through-
out the experiment the temperatures ranged from 26° to 38° C. At 8 p. m.
July 24 these insects were removed from the soil in the bell-jar and reweighed.
Group A from the desiccator weighed 8.53 grams, showing a loss of 3.63 grams,
and group B from the humidor weighed 10.92 grams. Previously a box of soil
(90 by 60 by 15 cm.) had been filled with a mixture of equal parts of sand and
adobe, which also had been already saturated with water and was kept slightly
moist throughout the experiment. Two bell-jars (a humidor and a desiccator)
were placed side by side over the slightly moist soil in the above box; insects of
group A were placed in the latter, and those of group B in the former; after
28 hours group A was in hibernation, but group B did not hibernate, although
the beetles remained active upon the filter-paper. The calcium chloride was
now removed from the bell-jar over the hibernated group A, and the soil was
kept saturated ; at the end of 3 days 12 beetles emerged and after 6 days 57 more
beetles were discovered, but at the end of 2 days no others had emerged; the
soil was then sifted and 31 dead beetles were found. The individuals of group
B still remained active, but none, however, had hibernated. These results
show clearly that in the summer generation “ induced ” hibernation with a high
death-rate may be produced through desiccation and, furthermore, that when
water-balances were restored, all the living individuals emerged again and
resumed the activities normal to their generation and season.

To further substantiate the above conclusions other tests follow. In the
fall generation, which hibernates normally, 1,000 newly emerged adults (Tucson
A, g. IV) were collected on August 14, and divided equally, regardless of sex,
into the following four groups: Each group was placed immediately in a
separate wire-netting tube in the screened vivarium at Station A, and the tubes
were made of wire-netting (95 cm. deep and 35 cm. in diameter), with a similar
material covering the top. These were sunk 55 cm. into adobe soil composing
the bottom of the vivarium, and each tube was filled to a depth of 53 cm. with a
mixture of equal parts of sand and adobe.

368 RELATION OF WATER TO THE BEHAVIOR OF

The following conditions were experimentally planned in tube 1, containing
250 beetles, to give a low rate of evaporation, and the soil was kept moist by
adding water each morning and evening. This tube was kept filled with sprays
of Solanum hertwigti, which were kept fresh by having the stems in 250 c.c.
bottles filled with water, and the sprays were renewed twice daily; it was also
necessary to wrap tinfoil about the top of the bottles to prevent the beetles from
drowning. The environmental conditions were apparently normal, for the

TABLE 10.

Tube 1. Tube 2. Tube 3. Tube 4.
Food and moist. Food and dry. No food and dry. |No food but moist.

When observed.

ration.
hibernated.

No. of beetles
o, of beetles
dead.

ate of evapo-
No. of beetles

above ground.
No. of beetles
above ground,
above ground.

Be
fea

°
|

°

>

°

o. of beetles

hibernated.
o. of beetles

Rate of evapo-

Rate of evapo-
dead.

Rate of evapo-
ration.

No. of beetles
above ground.
o. of beetles
hibernated.

No. of beetles
ration.

hibernated.
dead.
No. of beetles
No, of beetles
No. of beetles

| R

|

es
is

ia)

COR DOH DHOMDHPONWDORHENENOHK OWN GE:

August 1

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m.
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m.
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m.
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.2/222| 0} 28)18. 0| 157! 93 0|129/121 177; 0
Tubes removed, soil sifted, and all hibernated adults found
to be alive.

SN WRONROQRPATIWORNOINARANQRK AIR D

>
WODH ND WAWNaWINWOONWHONHKOWNOT:
CU wDNSDONSONOUNSNONNBDONDO
KH BOONAMNAMNORANIWOWOWOMNON DHA OND
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a.
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as

water-condition, the food-supply, the low rate of evaporation, and the soil-
moisture were all favorable for the normal activities of the animals used (Table
10 for tube 1) in this problem.

The following set of experimental conditions was maintained in tube 2, which
contained 250 beetles; however, in this case the soil was kept only slightly
moist and the first 5 cm. was used as a dry mulch, so that less moisture was lost
through evaporation. The same food plants, Solanwm hertwigw, were added

Tue Porato BEETLE IN A DESERT 369

thrice daily, but only a few small sprays were used each time, so that the air
within the tube was free from dampness, a condition which would have increased
the evaporation rate and assisted in making the environmental situation un-
favorable. The environmental conditions in this case were normal, in so far as
the food-supply was a factor; but the other surroundings were modified, at
least as to the high rate of evaporation (Table 10 for tube 2). Both tubes 1 and
2 were planned to give the ascertained differences in evaporation-rates ; accord-
ingly tube 1 produced a lower and tube 2 a higher rate, but the food relations
for both were approximately normal.

No plants were used in tubes 3 and 4, but each tube was wrapped with several
thicknesses of coarse absorbent paper ; at the beginning of the test the soil within
each was saturated with water, but no water was added during the experiment.
Around the outside of tube 4 was placed a coil of lead-tubing drilled full of
holes, and this was connected to a carboy of water. This device kept the
absorbent paper surrounding the tube saturated and, furthermore, a large piece
of oil-cloth was wrapped to the height of 15 cm. around the base of the tube
and beneath the absorbent paper. This oil-cloth was extended out in all direc-
tions for about 60 cm. from the bottom of the cage, so that the dripping water
did not come in direct contact with the soil in the tube. On the other hand, no
water was added to tube 3, so that this cage was kept dry during the experiment.
These conditions, therefore, produced a high rate of evaporation in tube 4 and a
low one in tube 3 (Table 10). The results for each of these tests follow.

The 1,000 beetles used in this experiment were grown under the same environ-
mental conditions and from the same parents, and, moreover, these animals had
emerged as adults from the pupa state synchronously; so they were then as
nearly uniform physiologically as it was possible to obtain them. The con-
clusions showed for tube 1 with plenty of food and moisture, when the indi-
viduals were counted at the end of the experiment, that there was no hiberna-
tion ; 28 were found dead upon the soil. In tube 2, with plenty of food, but in
which the air was kept dry, the census, when taken at the end of the test, showed
that 157 had successfully hibernated and that 93 had died. At the end of the
experiment tube 3, which contained dry air and no food plants, showed 129
beetles in hibernation and 121 dead ones. Tube 4, which was supplied with
moisture but with no food, at the end of the test gave no evidence of hibernation ;
73 of the 250 beetles originally present were found dead upon the soil. These
results proved that newly emerged adults of the fall generation can not be
caused to hibernate under normal conditions, but that if the surrounding
medium was dry a type of hibernation reaction did result through desiccation.
Such deductions are possible, since the evaporation rates in Table 10 show that
a low rate retarded hibernation and a high one accelerated this behavior.

It is also true that this entrance into hibernation may be of the normal type,
which always occurs under normal conditions in the winter generation. Low
temperature, however, was an important factor at Chicago, but this kind of
hibernation also took place in the pure winter-generation stock, even under high
temperatures. This behavior was further studied in the second generation of
the year under the following set of experimental conditions.

At Tucson Station A this type of hibernation reaction in beetles of the winter
generation (Tucson A, g. II) was observed to appear under a normal environ-
mental complex in the fall of 1911, but all other hibernations (Tucson A, g. IV),

25

370 RELATION OF WATER TO THE BEHAVIOR OF

which took place under adverse circumstances in the early fall of 1912, were of
the induced type. At Tucson Station B this behavior was not discovered in
either the winter generation of 1911 or that of 1912, since the environmental
conditions always produced desiccation in the early fall at this locality, thus
causing the beetles to be in hibernation about 10 months each year ; they emerged
about the middle of July, and after feeding for a short period re-entered hiber-
nation late in August. At the Chicago Station, however, normal hibernation
always occurred, because the environment was normal, for no excessive desicca-
tion or any other climatic adversities appeared. It became necessary, therefore,
to determine if these results could be confirmed by further data, so the following
hibernation tests were carried out.

For these tests 30 emerging adults (Tucson A, g. II) on September 2 were
placed in a hibernating pedigree-cage containing potato plants for food; the
soil was a mixture of equal parts of sand and adobe, and water was added twice
daily, but the plants completely filled the cage. The experimental conditions,
therefore, were apparently normal throughout the test. It was discovered by
daily observations that these animals were in hibernation on September 18 and
when dug up on October 2, the first adults were uncovered at a depth of 20 cm.,
but the larger number of beetles were found at the bottom of the pot. The
beetles were inactive when first removed, but began to move in a few minutes at
an air-temperature of 33° C. Various tests in the field demonstrated that they
possessed no reactions to food or dry soil, but within 5 minutes they did respond,
and all burrowed into the moist earth at a temperature of 21° C. This indicated
that a cool moist soil accelerated the entrance reaction. These results were
further tested to determine if similar reactions always took place.

On September 2, 130 emerging adults (Tucson A, g. II) were put into a
hibernating cage, which had been previously filled with potato plants, and in
which the soil consisted of a mixture of equal parts of adobe and sand, to which
water was added twice daily; thus the conditions were approximately normal,
for no desiccation occurred. The beetles responded to this set of conditions,
for they were in hibernation by September 22. When dug up on October 21
the insects were found distributed through the soil from the top to the bottom
of the cage, but when tested in the field showed no reaction to food or dry soil,
and when brought into contact with cool moist soil, out-of-doors, they burrowed
into it within 5 minutes.

This activity was again tested in the following manner: 51 emerging adults
(Tucson A, g. IL) were removed September 3 and were placed in a hibernating
cage filled with Solanum hertwigu for food. In this experiment a different
food plant was also used, but with no apparent result upon their behavior. The
soil was also of equal parts of sand and adobe, and water was added each morning
and evening, so that the experimental conditions were apparently normal. All
the animals were in hibernation by September 19, but when dug up on October 3
only 46 adults were alive. The first individuals, however, were discovered at
a depth of 29 em., and the majority were at the bottom of the pot. When
tested in the field no reactions to food or dry soil were observed, but when
brought into direct contact with cool moist earth all burrowed into it imme-
diately. Thus when normally hibernating beetles of the winter generation were
removed from hibernation a cool moist soil was necessary to initiate this
behavior.

Tur Potato BEETLE IN A DESERT ov1

ACTIVITIES DURING HIBERNATION.

It was observed that hibernating beetles were inactive when first dug from the
soil, and if the insects were moved to a warm room they soon began to crawl;
then entrance into hibernation occurred if they were brought into contact with
moist earth. At Chicago, during the winter of 1911-12, it was observed that
beetles which had hibernated out-of-doors migrated more deeply than usual
during the cold winter. From the following test it appeared that beetles would
move to moist regions in the earth during hibernation, for late in April 1912,
at Tucson Station A, several hundred individuals were found to be hibernating
in the open air cage. Accordingly a corner of this cage was watered and the
soil was sifted ; thus, all the beetles were removed in that locality, but the newly
dug soil was kept moist, and each week it was examined for adults ; during each
observation a large number was always discovered.

WATER RELATION OF SOILS AND HIBERNATING BEETLES.

The beetles hibernate in small cavities or cells, which contain air of a relative
humidity, that is in proportion to the water-content of the surrounding earth.
During heavy rains the soil becomes flooded with water, so that some air is
driven from the cavities, but if the rain continues for too long a period the
beetles may die. On the other hand, if the soil is too dry, desiccation of the
insects takes place and death may result; therefore, the part soil-moisture plays
in mortality during hibernation is of great significance. Tower (1906), in
discussing results with soils, states:

“The water-content of soil is controlled, not by an abundant rainfall, nor by
telluric water, but almost wholly by adhesion and capillarity in the soil—that
is, physical conditions alone, such as permeability, capillarity, and the power to
absorb and to retain water are the factors which influence the moisture content
of soil . . . . Inall soils the pores which do not contain water are filled with air
in which the percentage of relative humidity is controlled by the amount of
water in neighboring pores. Likewise, the cells in which these beetles pupate
are filled with air; the relative humidity is controlled by water in the pores of
the surrounding earth.”

Thus the physical composition of the soil is important in preserving insect
life, and the adobe soil of the Tucson Desert, although it contains but little
moisture, does possess other physical potentialities which act in retaining
moisture, for through drying it becomes impervious to water and hibernating
animals are sealed up in their cells and thus preserved from desiccation. To
determine how dry the adobe soil was when containing living beetles, samples
of it were taken from the walls of the cells (Table 11) and those of June 30

TABLE 11.

Date. Depth. Wet soil. Dried soil. Water-loss. Water-content.

cm. gms. gms. gms. H,O. per cent H,O.
Ape Vos is. as 25 60.93 56.18 4.75 8.45
ADT Ss. 6.33.5 25 122 .22 110.00 T2322 ys
April. 30... .<. 25 123.84 115.89 7.95 6.85
5 58.94 57.64 L380 2.25
June 30...... 10 76.55 73.55 3.00 4.07

20 58 .09 55.45 2.54 4.45

372 RELATION OF WATER TO THE BEHAVIOR OF

showed an average of less than 4 per cent water of their dry weights. This
was during the dry season, when no beetles had emerged from hibernation up
to the above date, but on July 1, the day following, 0.98 inch of rain fell; 73
beetles emerged on July 2, and by July 3 eggs were laid. This sharp response in
behavior must be attributed to the water-content of the soil, for the beetles
emerged immediately after the first rain and oviposition took place within
48 hours. The insects of the surrounding desert showed a similar response,
inasmuch as the adobe soil held them imprisoned until the first rain, which
raised their water-content and softened the soil so that emergence of immense
numbers occurred.

The following experiment was performed to show the relation of physical
composition of soils to mortality during hibernation. Three hibernating cages
were prepared containing soils, one was composed of sand, another of adobe, and
a third of equal parts of sand and adobe. On October 1, 500 hibernating adults
were caused to hibernate artificially in each tube by placing the insects at a
depth of 40 cm. in the soil, and the soil within each tube was kept slightly moist
until late in October; they were then allowed to remain out-of-doors under
natural conditions during the winter until May 1, when water was added to each
cage. On May 3, 362 adults emerged from the soil mixture, 251 from the adobe,
but none from the sand. On May 5, the soil of each cage was sifted, when it
was found that all in the pure sand were dead but that only 27 in the adobe
and 23 in the soil mixture had succumbed. It appeared, then, that there was a
relation between soil composition and mortality during hibernation, for the
sand permitted excessive desiccation to occur, the adobe and mixed soils did
not admit of great desiccation, but most individuals were hibernated suc-
cessfully in the mixture of equal parts of adobe and sand.

EMERGENCE FROM HIBERNATION.

The physiological complex of emerging beetles was next considered in refer-
ence to two phases of the problem. In one case the reactions of hibernating
beetles caused to emerge by applying water to the soil were determined, and in
the other the reactions of similar adults, in which emergence was produced by
sifting the soil, were tested. In the first experiment hibernating beetles (Tucson
A, g. II) were encouraged to emerge by applying water on June 1, when they
were removed to the constant-temperature room; their reactions were found to
be positive to light, but negative to gravity. The light response was further
tested by placing 5 beetles in each of 10 test-tubes and each tube was placed so
that one-half of it was in the shade of the laboratory roof and the other half
in direct sunlight. The beetles all oriented and moved out into the sunlight
at the end of each tube, where they remained, and in a few minutes were dead.
The air-temperature in the exposed ends of the tubes was 57° C. In this experi-
ment the organisms reacted to sunlight and the suggestion that possibly the red
or blue rays might have influenced this result led to the next test.

Of 50 hibernating individuals (Tucson A, g. IL) emerged after adding water
on June 3, 25 were put in each of two test-tubes; one of which was placed in
direct sunlight under a red bell-jar containing a potassium-bichromate solution,
and, while no deaths occurred, no definite reaction was observed ; the other was
placed in the direct sunlight beside the former, under a blue bell-jar provided
with a solution of copper sulphate, when all became positive to the rays and

Tur Potato BEETLE IN A DESERT 373

none died. We may therefore conclude that death in the first experiment was
due to heat.

Many tests of various kinds have been given elsewhere and with the same
result—that when hibernating beetles were caused to emerge by applying water,
they reacted positively to light and negatively to gravity. The next experiment
consisted in testing the reactions of hibernating beetles, in which emergence
was attained by digging and no water was added to the cage.

For this test 47 hibernating beetles (Tucson A, g. II) were removed by
digging at 8 p.m. on June 12. They were negative to a 32 c. p. lamp, but 23 of
these insects were positive to candle-light of a weak intensity. These were
immediately placed under a bell-jar containing moist filter paper, and when
tested on June 13 they were found to be positive to light but negative to gravity.
This behavior was repeated in the following case.

Twelve hibernating beetles (Tucson A, g. II), when removed by digging at
? p.m. on June 20, were found to weigh 1.2573 grams, but they gave no response
to light or gravity. (A soil-sample taken from the earth surrounding the beetles
showed that it contained water to the extent of 12.7 per cent of dry weight.)
When the animals were placed in a humidor at 10 a. m. on June 22, they
weighed 1.3057 grams, having absorbed 0.1484 gram of water from the moist
chamber; 10 of these beetles, when tested, were positive to hight, but 2, which
were inactive, died in a very short time after the experiment. The 10 adults
were also negative to gravity, for when placed in the constant-temperature dark-
room, all crawled to the top of the cylindrical wire-netting tube. These experi-
ments showed that positive phototropic and negative geotropic reactions were
induced in hibernating beetles by increasing the water-content of the surround-
ing medium, because the beetles under the moist bell-jar increased in weight and
imbibed water directly from the moist air. It was also true that they absorbed
water from the air in the soil. This relation was further shown in the following
observations, which were made upon the emergence response.

The time of emergence is controlled by the environmental complex, for if
water were added to the medium surrounding hibernating beetles, when the soil
temperatures were above 14° to 16° C., emergence resulted. This was evident
at Tucson, for no emergence was discovered at either station until the rainy
season in July, and furthermore, the winter rainy season caused no emergence
because of low temperatures. At Chicago, emergence occurred whenever the
soil-temperatures reached 14° to 16° C., for enough precipitation always took
place during the winter and spring months so that emergence occurred as soon
as the proper temperature relations existed, which was from May 20 to June 25.

SUMMARY AND DISCUSSION UPON THE RELATION OF WATER
TO HIBERNATION.

The conclusions arrived at from these previous results indicated that a type
of hibernation might be produced at any time through desiccation, except with
low temperatures, when little desiccation took place. This condition produced
a loss of water from the beetles in such a way that they responded negatively to
light and positively to gravity, so that they burrowed into the soil and remained
there until the moisture-content of the soil was sufficiently high. They then
absorbed hydroscopic water, which raised their water-content and reversed their
reactions, so that they became positive to light and negative to gravity, hence

o74 RELATION OF WATER TO THE BEHAVIOR OF

their emergence, so that now, in case other conditions were suitable, they were
ready to enter upon their reproductive activities. Below 12° to 15° C. in soil-
temperature the water-relation was not the controlling factor, but the duration
of the hibernating period depended upon the length of the dry season in an arid
complex and upon the length of winter (low temperature) in a temperate
region.

Baumberger (1914) reviews, at length, the literature on hibernation of insects
and reaches the following conclusions, chiefly from his own researches :

“1. That temperature is but a single factor and not necessarily the con-
trolling one in hibernation.

“2. That hibernation is usually concomitant with overfeeding and may be
the result of that condition or the result of accumulation of inactive substances
in the cytoplasm of the cell due to feeding on innutritive food.

“3. That the loss of water which is general in hibernation probably results
in a discharge of insoluable alveolar cytoplasmic structures which have accumu-
lated and produced premature senility with an accompanying lowering the rate
of metabolic processes.

“4, That starvation during hibernation, together with loss of water, may
result in rejuvenation, when aided by histolysis, and an increase in permeability.

“5. That this rejuvenated condition and increased permeability will, if
stimulated to activity by heat, permit pupation in codling-moth larve, which
in this case is the termination of the hibernating conditions.”

The results of Sanderson and Peairs (1913) add another condition for
hibernation that was also discovered by Tower (1906) for the potato-beetle ;
this is the influence of heredity. The former authors reached the following
conclusions :

“That our first work was an effort to show that emergence from hibernation
was due to an accumulation of temperature, but it soon became apparent that
hibernation is very largely controlled by the influence of heredity, and that the
relation of the temperature and inheritance must be determined for each
species.”

For the Mexican cotton boll weevil, Hunter and Hinds (1904) found that
dryness was more desirable for hibernation and that mortality during hiberna-
tion was greater from exposure to moisture than from cold; but, on the other
hand, high temperatures and moisture were the best conditions for the develop-
ment of such beetle larve. In this connection, Baumberger (1914) stated:

“The effects of ether on plants is similar to hibernation and since the action
of ether is probably a drying one, this may throw light on the importance of
moisture in hibernation.”

Loeb (1906) says:

“The lack of water acts similarly to a low temperature. This is the reason
why seeds can be kept alive so long. Lack of water may reduce the reaction
velocity of the hydrolytic processes in seeds at ordinary temperature so con-
siderably that it may become practically zero.”

The snail, according to the results of Kiihn (1914) loses weight in winter
and reacts to drought in summer. Unless it contains a large amount of water,
no dry food is taken, and if placed under moist conditions when in hibernation
it will come out of its closed shell. Bellion (1909) finds that a low moisture-
content of the air is the determining hibernating factor in the European snail,

THE Potato BEETLE IN A DESERT 375

and Baker (1911) shows that snails during dry seasons form an epiphragm ;
they usually bury themselves during hibernation and estivation. On the other
hand, Pearl (1901) finds that the terrestrial slug Agriolimaz can hibernate in
cold water.

In the vertebrates, Rulot (1901) determines for the bat that the proportion
of water increases during hibernation from November to April; but there
actually was a loss of water, more in proportion at the end than at the beginning.
Polimanti (1904) finds that an increase in humidity increases the pounds in a
marmot during hibernation.

In conclusion, the work of Sanderson (1908) agrees most closely with my
results upon hibernation. In discussing the relation of temperature to the
hibernation of insects, he states:

“Tn come cases, however, the time of emergence from hibernation is con-
trolled by moisture conditions as well as temperature, or independent of tem-
perature. Thus Tower kept the potato beetle in hibernation for 18 months at a
high temperature but with a dry atmosphere, and they emerged as soon as
normal moisture conditions were produced. Webster and Hopkins have shown
a similar effect of the lack of rainfall on the emergence of the Hessian fly in the
fall. In relation to hibernation in humid climates the matter of moisture is
probably not a controlling factor, but undoubtedly has the most important
influence upon the time of emergence of forms in estivation during the summer
or in an arid region.”

My results upon the potato-beetle substantiate the work of Sanderson.

EFFECT OF CHANGES IN WATER-CONTENT UPON ALTERATIONS
IN TROPIC ACTIVITIES.

The experiments and observations upon L. decemlineata proved that, when
surrounded by a moist medium, the beetles were positive to light and negative
to gravity. It is also evident from previous tests that if the moisture of the
surrounding medium was decreased, desiccation resulted, so that the insects
were reversed in their behavior and reacted negatively to light and positively to
gravity. These beetles, however, responded to any intensity of light if moved
from a lesser to a greater intensity, and accordingly when moved from darkness
into the moonlight at Tucson they always reacted ; and in many instances insects
which were negative to a strong light were also positive to a weak one.

It was shown by Burdin (1913) that heat and dryness stimulate positive
reactions in terrestrial amphipods, while cold, moisture, and quiet favor nega-
tive reactions. The results of Dice (1914) prove that light of high intensity
makes daphnias positively geotropic, but a decrease in light intensity has the
reverse effect; and furthermore, these animals tend to become positively
geotropic in high temperatures and negatively geotropic in low. Kanda
(1916a), in studying geotropism in a marine snail, found that it is negatively
geotropic, but most individuals would orient positively if placed on a dry glass
or wooden plate. Later, Kanda (1916b) demonstrates for fresh-water snails
that they are negatively geotropic when their lungs are empty and positively
geotropic when their lungs are full of air. Olmsted (1917) finds that food is a
factor in the reversal of the behavior to gravity in Planaria maculata. Adams
(1903) concludes that earthworms retreat into their burrows during the day-
time because of their negative phototropism, but they emerge at night not so

376 RELATION OF WATER TO THE BEHAVIOR OF

much because of darkness as because of their positive phototropism for faint
light. Wilson (1891) shows that Hydra is negative to bright light and positive
to dim light. According to McGinnis (1912), Branchipus serratus is positively
geotropic in light and negatively geotropic in darkness; darkness rather than
light may furnish the stimulus to this reversal. In studying the reactions of
Drosophila to gravity, Cole (1917) finds that the response to gravity is much
less marked in flying than in creeping, where it is very definite.

Many animals orient in the field in relation to the center of gravity of the
earth. Loeb (1905) found that some animals turn their heads upward and
others downward. ‘To this latter class belongs the garden spider, which he
found may hang in this position in the center of its web for hours. He dis-
covered the same behavior in some diptera. Shelford (1917) states that such
animals as the grasshopper usually orient with the head up, while aphids and
katydids orient with the head down. In the potato beetle the majority of
larve and a large number of adults orient with the dorsal side down.

There is a vast amount of literature dealing upon reversibility in photo-
tropism through chemical agencies. Loeb (1893 and 1904) proves that it was
possible to reverse the reactions of a large number of water forms through
chemicals such as salts, acids, and the like. According to Moore (1912a, 19126,
and 1913), phototropism in Daphnia and Diaptomus may be influenced through
the agency of caffein, strychnin, atropin, acids, alcohol, and ether. Moore
(1913) says:

“ While negative phototropism in Diaptomus can be reversed by acids, but
positive phototropism brought about by chemical means can not be reversed by
strychnin (atropin or caffein).”

Wolfgang (1912) determines that electrolites influence phototaxis, and
Kanda (1914) reversed geotropism in Arenicola larve by means of salts.

EXPERIMENTS UPON THE ROLE OF WATER IN GEOTROPISM.

On May 15, at 8 p. m., 21 freshly emerged beetles (Tucson A, g. I) were
moved to a constant-temperature room and tested 10 times as to their reactions
to gravity, and in each test all were negative. These geotropic reactions were
tested in the dark, and if the beetles crawled to the top of the tube, when held
in a vertical position, they were considered as positive and if they crawled to
the bottom as negative. The thermograph tracings showed a constant tempera-
ture of 21° C., with a daily variation of 1° C., throughout the test. Again at
11 a. m. on May 16, when tested as previously (10 times), they were still
negative to gravity, and at this time weighed 2.0009 grams; furthermore, on
May 17 at 10° 30™ a. m., they weighed 1.9294 grams, and again gave the same
test to gravity, so that these results proved that the beetles under these con-
ditions were uniform for this reaction. For experimental purposes these insects
_were divided into three groups. The first group of 7 adults was put into a
calcium-chloride chamber, which produced so high a rate of evaporation as to
desiccate them; the second of 7 individuals was subjected to a low rate of
evaporation by placing wet filter-paper under the bell-jar, so that little water
was removed from them under these conditions; in the third chamber 7 adults

Tue Potato BEETLE IN A DESERT ore

were used as a control. In table 12, the results are given, which shows that
group 1 at the beginning of the test was negative, but by 9 30™ a. m., while
under the dry bell-jar, all became positive, but when moist conditions were
restored in the jar, by 10 a. m. on May 26, they were again negative. In group 2,
at the beginning, all were negative and remained thus as long as they were kept
under moist conditions, but at 10 a. m. on May 30, all had become positive. In

TABLE 12.—Reversal in the potato beetle to gravity.

Date and hour of observation.

Weight of
Positive to
gravity.
Negative to
Weight of
beetles.
Positive to
Negative to
Weight of
Positive to
gravity.
Negative to

o
-
5
~
3
el
©
[on
&
o
a
»
—_
<j
°C

2

J S
eaoqoooos

May 17, 10° 30™ a.
30 p.
30
00
00
00
00
00

Note.—In group 1 the conditions in bell-jar were dry on May 17, 19, and 21, and
moist on the other days. In group 2 said conditions were dry on May 26, 28, and 30,
and moist on other days. In group 3 said conditions were uniform throughout.

group 3, which were the control individuals, a gradual loss of weight occurred
until 10 a. m. on May 28, when all were positive. These results showed clearly
that reactions to gravity may be reversed through changes in the moisture-
content of the surrounding medium.

RELATION OF TEMPERATURE TO THE OUTGO AND
INTAKE OF WATER.

An interesting discovery was the determination that there was little absorp-
tion of water below 12° C. as was shown in a test in which beetles emerging
from pupation were collected on July 28; they were placed under a bell-jar
containing wet filter-paper, where they remain until 12 midnight on July 30,
when equal numbers of insects were placed in two bell-jars, in a refrigerator, at
a temperature of 10° to 13° C. One bell-jar contained wet filter-paper and the
other calcium chloride, but weighings made at frequent intervals showed that
in the humidor there was no appreciable loss during the 84 hours in the
refrigerator. In another test, desiccated beetles were placed under saturated
bell-jars in the refrigerator, but weighings made at frequent intervals gave no
evidence of water-absorption. These results showed how much organisms were
protected from absorbing water during winter rains, which would otherwise
result in their freezing, and further demonstrated that desiccation, occurring
slowly at a low temperature, was a factor in the economy of the organism.

A similar result was obtained with upper temperature limits. It is known
that the coagulation temperature of colloids varies with the amount of contained

378 RELATION OF WATER TO THE BEHAVIOR OF

water, a condition with which our results on LZ. decemlineata agreed generally,
since the death-point in potato beetles with a high water-content was 58° to
60° C., and desiccated ones withstood 1° to °5 higher temperature. Bachmet-
jew (1902) shows that the temperature of the insect’s body varied with the
conditions, namely, moisture, temperature, and the like. If the air was damp,
the body-temperature was higher than that of the surrounding medium, since no
evaporation occurred; but if the air was dry it cooled through evaporation.
He also pointed out that the smaller the percentage of fluids in a unit of the
living insect body, the lower was the normal congealing-point of the fluids.
Tower (1906) states that soil-temperatures taken on the savannas of Vera Cruz
in April 1904, in places where L. decemlineata was estivating, were frequently
as high as 60° to 65° C., and that success in passing through these high tem-
peratures at the end of the dry season depended upon the completeness of the
physiological changes preceding entrance into hibernation. These results were
similar to those just given for this insect, which showed that the lower and
upper temperature limits were influenced through water-relation.

In studying longevity in insects, Baumberger (1914) shows that the tem-
perature at which colloidal substances coagulate lowers with a decrease in
water-content and that long exposure to cold or high temperature may result
in this decrease in water. He explains that the result of a long exposure to cold
is the same as short exposure to heat, while intensity of cold shortens the length
of the period. He also demonstrates that the point of coagulation varies with .
the water-content of the insects studied. Greely (1901) concludes that:

“ A reduction of the temperature and a loss of the water have similar effects,
because the cell loses water when the temperature is lowered, as well as when
the concentration of the surrounding medium is raised.”

The results of Livingston (1903) show for Spirogyra that a cell loses water
when the temperature is lowered. In discussing the reversal in animal instincts,
Loeb (1900) concludes that a decrease in temperature has the same physio-
logical effects as a loss of water.

METABOLISM AND THE WATER-RELATION.

The results of various workers show that desiccation modifies the rate of
metabolism; thus, the alterations in the behavior of the potato beetle may be
due to differences in metabolic activity, brought about through combined rela-
tions of water and temperature of the organism. Shelford (1913) states that
the changes in activity of the animals used in his experiments were due to the
withdrawal of water.

It is known that anything which disturbs the rate of metabolism in an animal
alters its response to a stimulus, and that reversed reactions in behavior are
caused by changes in this metabolic process. According to Jennings (1904),
Child (1910), Wodsedalek (1911), Allee (1912), Phipps (1915), and others a
stimulus may change the physiological state of an animal, which produces a
modified type of reaction. Many depressing agents are also known, such as
potassium cyanide, chloretone, and a low oxygen content. Baumberger (1914)
shows that starvation is an agent of this character, since it decreases metabolism
by removing material to be oxidized. Loeb (1906), Mast (1911), Shelford
(1914), and others further demonstrate that acids and alkalis increase irri-

THE Potato BEETLE IN A DESERT 379

tability. The results of Shelford (1914) and of Chenoweth (1917), however,
agree most closely with those which are recorded in this paper. Both of these
observers conclude that a high rate of evaporation increases sensibility or irri-
tability through loss of water, a condition which might account for the altera-
tions in the reactions of the potato beetle.

GENERAL DISCUSSION UPON THE ROLE OF WATER IN
LIVING THINGS.

In order to show why such a large number of reactions in the potato beetle
were controlled by its water-relation, it was considered necessary to review only
literature which bore directly upon these studies. “It was assuredly not
chance,” to quote Henderson (1913), “ that led Thales to found philosophy and
science with the assertion that water is the origin of all things.” He also states
that the action of water now appears to be a momentous factor in geological
evolution, and the physiologist has found that water is invariably the principal
constituent of living organisms. Thus, according to this observer, water makes
up from 70 to 85 per cent of fishes, about 87 per cent of oysters, 85 per cent of
apples, 78 per cent of potatoes, and 95 per cent of the edible portion of lettuce.
It is interesting in this connection to add that my results upon the potato beetle
show it to contain 80 per cent water. Henderson further says that the organism
itself is essentially an aqueous solution in which are spread out colloidal sub-
stances of vast complexity, and as a result of these conditions there is hardly a
physiological process in which water is not of fundamental importance. Accord-
ing to Livingston (1903), it is absolutely essential that every living mass of
protoplasm be saturated with water, since vital phenomena occur solely in
aqueous solutions.

Physiologists have long recognized that water is of the greatest importance
for normal activity of tissues and that all exchanges of material, all supplies of
food, and metabolic processes in general are dependent upon it. Aberhalden
and Hall (1908) assert that water is absolutely necessary as a solvent for
numerous compounds, for it brings into play various chemical reactions, which
take part in building up and breaking down substances without number; it is
also a carrier of nourishment to the body and provides the means for the removal
of its waste products. In discussing the physical importance of water, Hammar-
sten and Mendel (1911) show that water by its evaporation is an important
regulator of temperature. Davenport (1897) states that growth is due chiefly
to imbibed water, and Estabrook (1910) also demonstrates that growth in
parameecium is due almost solely to inhibition of water. MacDougal (1912),
Lloyd (1905), and others demonstrated that many plants absorb water directly
from the air. In respect to this subject, in animals the frog has perhaps
received most attention, and according to Hill (1908) frogs take up water
through the skin; they do not drink, for a thirsting frog with its gullet tied
increases in weight no less than one with the gullet open. He also states that a
frog can be gradually dried to less than 39 per cent of its normal weight with-
out fatal results. My own data for the potato beetle show that it can be desic-
cated to less than 50 per cent and still live, while Catalpa lanigera will die if
reduced by 25 per cent and the June bug if dried less than 15 per cent of its
normal weight.

380 RELATION OF WATER TO THE BEHAVIOR OF

It is not true that all animals do absorb water, for my experiments upon the
scorpion and horned lizard (Phrynosoma cornutum) of the Tucson Desert indi-
cated that these animals would not imbide any aerial water, and even when
immersed in it no absorption was detected; furthermore, when desiccated no
difference in weight was observed. A large scorpion lived for more than 2
months in‘a desiccator without food, but it probably died of starvation. If
lizards do not absorb any appreciable amount of water or lose any through
desiccation, then such a condition might demonstrate why they are distributed
in a desert as well as in a hot humid region; therefore, the water-relation would
not be the determining factor in a lizard’s habitat, but the temperature-relation
should be of greater importance in determining its distribution. This might
also account for the results of Weese (1917), since he studied the reactions of
the horned lizard to evaporation and temperature gradients, but found that the
lizard responded definitely to temperature, while there was no marked reaction
to evaporation. In this connection the work of Matthews (1913) is important.
He says:

“There is a mechanism for rendering mammals tolerably independent of the
moisture content of their environment, a mechanism most highly developed in
the reptiles. A mechanism formed by the replacing of the wet skin of the
amphibian by a dry or scaly skin; the perfecting of the kidneys to maintain
osmotic pressure of the blood; the control of the sweat glands and loss of water
by the intestines ; the development of membranes non-permeable to salts so that
dtimals may sit in fresh water ace hae Salts.0 = Gia. By this improvement
reptiles have secured almost complete independence of the water-content of
their surroundings.”

Water is essential to life, says Babcock (1912), for during the period of
development it is the most abundant constituent of living organisms. He
continues :

“Some of this water is imbibed directly, some of it is taken with solid food
which is rarely dry, and some of it is formed within the organisms by metabolic
changes in the organic constituents of the food and tissues, induced by respira-
tion and other vital processes. The relative amount of water derived from each
of these sources depends upon the kind of organisms, its period of growth, the
nature of its food, its environment, and its activities.”

His experiments show that many varieties of insects, such as the clothes-moth,
the bee-moth, and the flour-beetle, the flour-moth, and others live during all
stages of development upon foods containing less than 10 per cent of water.
He concludes that nearly all the water used by insects feeding upon air-dried
foods is metabolic. In my own experiments upon the potato-beetle and other
animals there are no data upon metabolic water and its relation to behavior.

The results of Hegner (1916) further illustrate the water-relation in animals.
He arranged an experiment upon oviposition in the potato-beetle, so that 35
batches of eggs were in the sunlight and 15 were in the shade. Those in the sun
came to nothing, but all in the shade were hatched. It was found that develop-
ment had started in the sunlight, but that desiccation probably arrested this
process; therefore he concludes that the advantage of concealment is not so
great as that secured by shielding the eggs from the desiccating properties of the
sun. My results show that the majority of adults orient to gravity with their
dorsal side down, which might explain why eggs are usually deposited on the
under side of a potato-leaf.

Tur Potato BEETLE IN A DESERT 381

SUMMARY AND CONCLUSION.

In general the results indicate for the potato-beetle that:

(1) The optimum breeding activity of this insect coincides with the highest
water-content of the atmosphere, since periods of oviposition are exactly con-
current with those of rain and low rates of evaporation.

(2) Differences in soil-moisture produce alterations in the water-content
of these animals which modify their behavior, since beetles will lay their eggs
sooner if they emerge from a soil of high moisture-content than if they issue
from a dry soil.

(3) Egg-production is also modified by differences in the evaporating power
of the air which surrounds these insects, since a low rate of evaporation en-
courages oviposition.

(4) The beetle dies if buried when all its activities are normal, but either
the summer or winter generation may be buried without injury if previously
desiccated.

(5) The adobe soil of the arid region retains a relatively high percentage of
water and is thus an excellent medium for the sustentation of the life of this
beetle, as in other desert animals.

(6) These insects exhibit a physiological behavior not unlike that of trans-
piration in plants; but further, their tropisms are modified by loss of water,
which is governed by the evaporating power of the air.

(7) The evaporating power of the atr surrounding these insects determines
their behavior through transpiration ; even their responses to light and gravity
are controlled by evaporation.

(8) Entrance into hibernation in a desert region may be produced at any
time through desiccation, except at low temperatures, when little desiccation
takes place.

(9) The hibernating period in an arid region is controlled by the duration of
the dry season, but is dependent upon the length of the winter in a temperate
region.

(10) The water-relation is the controlling factor in the emergence of this
insect from hibernation if the temperature is above 15° C.

(11) When surrounded by a moist medium (above 15° C.), either atmosphere
or soil, these beetles are positive to light and negative to gravity, but desiccation
reverses this behavior.

(12) This insect absorbs very little water below 12° C.; its death-point under
a high water-content was found to be 58° to 60° C., but when desiccated it can
withstand from 1° to 5° C. more of heat.

(13) Alterations in the behavior of the potato-beetle may be due to differ-
ences in metabolic activity as influenced through the water-relation.

(14) This animal also imbibed water directly, but no studies were made upon
metabolic water.

We may conclude that Leptinotarsa decemlineata, when introduced from its
grassland habitat into an arid region, is equilibrated immediately with respect
to its surroundings, especially in regard to its water and temperature medium ;
that its behavior is changed to resemble those responses still present in an
_ organism long accustomed to a desert complex, and that, since water is the

382 RELATION OF WATER TO THE BEHAVIOR OF

limiting factor in an arid region and the prime essential for metabolism, the
behavior of the potato beetle in a desert is determined chiefly by the water-
content of its environment. Henderson (1913) states:

“ Water, of its very nature, as it occurs automatically in the process of cosmic
evolution, is fit, with a fitness no less marvelous and varied than that fitness of
the organism which has been won by the process of adaptation in the course of
organic evolution. . . . In truth, Darwinian fitness is a perfectly reciprocal
relationship. In the world of modern science a fit organism inhabits a fit
environment.”

These results upon the potato beetle indicate that its marvelous fitness and
adaptation to water is such a “ reciprocal relationship.”

The experiments were performed at the Desert Laboratory of the Carnegie
Institution of Washington, and it is a pleasure to acknowledge my indebtedness
to its director, Dr. D. T. MacDougal, for his interest manifested. I must also
acknowledge my great indebtedness to Professor W. L. Tower, of the University
of Chicago, who made it possible for me to continue this problem at Tucson.
The following bibliography gives only the literature cited.

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THE Potato BEETLE IN A DESERT 383

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