Response of body lice, Pediculus humanus humanus, L., to blackbody radiation; with notes on their antennal morphology


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Response of body lice, Pediculus humanus humanus, L., to blackbody radiation; with notes on their antennal morphology
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153 leaves : ill. ; 28 cm.
Broce, Alberto Bolivar, 1942-
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Subjects / Keywords:
Blackbody radiation   ( lcsh )
Lice   ( lcsh )
Insects -- Behavior   ( lcsh )
Pediculus   ( lcsh )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )


Thesis (Ph. D.)--University of Florida, 1971.
Includes bibliographical references (leaves 145-151).
Statement of Responsibility:
by Alberto Bolivar Broce.
General Note:
General Note:

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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aleph - 000434295
notis - ACJ4010
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Full Text

Response of Body Lice, Pediculus humanus humanus, L., to
Blackbody Radiation; with Notes on Their Antennal Morphology






I greatly appreciate the personal interest in my

development and financial support offered by Dr. H. L.

Cromroy, chairman of my supervisory committee, during

my doctoral program.

Appreciation is gratefully extended to Dr. P. S.

Callahan, United States Department of Agriculture (USDA),

for his motivation, assistance and disposition of his

laboratories to m needs. I am indebted to the remaining

members of my supervisory committee, Drs. T. J. Walker

and D. H. Habeck, Department of Entomology, and Dr. H. A.

Bevis, Environmental Engineering, for their advice and

assistance with the manuscript. Special thanks are ex-

pressed to Dr. J. Gamble, Department of Botany, for his


A special note of thanks is due to Mrs. T. Carlysle,

USDA, for her assistance with the scanning and transmission

electron microscopes. Gratitude is also expressed to Mr.

D.'W. Anthony and Mrs. Jean Crosby, USDA, for their help

in transmission microscopy.


Thanks are due to Drs. D. Lindquist and D. A. Weidhaas,

USDA, for making facilities available at their laboratories.

My appreciation to Mr. M. M. Cole, and the rest of the

personnel at the lice rearing facilities of the USDA In-

sects Affecting Man and Animals Laboratory, for their co-

operation with the test insects. Appreciation is extended

to all the USDA staff who assisted during the course of

this research.

Special thanks to Drs. W. A. Bruce, W. Turner and

M. S. Mayer, USDA, for their encouragement, assistance and

criticism. Thanks are extended to my friends, Dr. B.

Federici and Mr. L. Goldman, for their help and suggestions

during this study.

Last, but not least, appreciation goes to my family

for their patience and understanding during this long

period of graduate study.









. . ii

S . vi

. . vii

. . *. ix

S. xiii




. . 1

. . 3

Reactions to blackbody IR radiation.
Morphology of antenna sensors .


The test insect. .
Behavior experiments .
Straight arena experiments
Round arena experiments..
CO2 monitoring experiments
Reactions to an artificial


. .


and varied stimuli .
Morphological studies of the antenna
Light microscopy . .
Transmission electron microscopy .
Scanning electron microscopy ...





Straight arena experiments .. 59
Round arena experiments 64
CO2 monitoring experiments 67
Reactions to an artificial finger
and varied stimuli. 82
The significance of blackbody
IR detection 85
The antenna morphology 89
Species comparison study 100
Function of the antenna
proprioceptive organs 102
Thetuft and pore organs 107
The peg sensors. .. 1

V CONCLUSIONS .. . .. 141




Table Page

1 Percent of the Total Number of Responding
Lice Recorded at Each Compartment in the
Straight Arena .. .. ... 60

2 Percent of the Responding Lice Moving
Toward the Blackbody and Aluminum Heaters
in the Straight Arena ... .. 61

3 Average Number of Lice Responding When
the Heaters Were On or Off in the
Straight Arena. . 62

4 Percent of Responding Lice Recorded in
Front of Heated Areas at 33 C in the
Round Arena . .. 65

5 Percent of Lice Recorded as Responding to
IR Stimulation in the Round Arena 68

6 Chamber Temperature and CO2 Concentration
When BB or Al Heaters Were Maintained at
33 C for 65 min. .. .. .. ... 71

7 Results of BB and Al Heaters Stimulation
Upon 50, One-Day-Starved Body Lice. 77

8 Results on CO2 Output of Lice When Either
the Al or BB Heaters Were Turned On and
Off, Alternately. . 79

9 Effect of Human Skin Air Emanations on
CO2 Output of 50 One-Day-Starved Body
Lice. . 81


3a, b

4a, b, c

5a, b, c



8a, b, c

9a, b

10a, b, c


Infrared Spectrum of Human Hand .

Infrared Spectra of Black Paint
(Minnesota Mining and Manufacturing
Co.) and Cellophane (Cigarette
Package Wrapping) ..

Infrared .Spectra of Rubber Glove and
Aluminum Foil, Heated to a 33 C
Surface Temperature .

Round Arena Apparatus .

Infrared Spectra of Infrared Radia-
tion Reflected at a 90o Angle from
Aluminum and Black Paint. .

A Schematic Diagram of the 2.5 cm
Strip Arena . .

CO2 Chamber for Monitoring Lice
Activity During Stimulation with
Blackbody Infrared Radiation .

CO2 Monitoring Flow Chart .

Flow Chart for Monitoring the CO2
Output of Lice During Stimulation with
Human Skin Gaseous Emanations .

CO2 Output of Lice During Constant
Stimulation Under Aluminum and
Blackbody Radiators, or When Both
Heaters Were Alternately turned
On and Off with a 2.5 Min Off
Period Inbetween. . .




Figure Page

lla, b CO2 Output of Lice During Periodic
Stimulation under Aluminum and
Blackbody Radiators . 76

12 Diagram of Adult Body Lice
Antenna . 90

13 Proprioceptive Sensors in the Antenna
of Adult Body Lice. . 103

14 Diagram Illustrating the Arrangement
of the Blunt and Pointed Setae on the
Tip of the Antenna of Adult Body
Lice.. . 113



Plate Page

1 Dorsolateral View of Left Antenna of
Adult Body Louse. . .... 92

2 Ventrolateral View of Left Antenna of
Adult Body Louse. . 92

3 Fourth and Fifth Segments of Adult
Body Louse Antenna. .. .. 94

4 End View of Antenna Tip of 1st Instar
Larva of the Body Louse . 94

5 Antennal Tactile Hair, Innervating
Dendrite and Neuron Cell; Axon Extends
Toward Antennal Nerve . 97

6 Campaniform Sensilla on the Second
Segment of the Antenna of the
Body Louse. . .. 97

7 Campaniform Sensilla on the Second Segment
of the Antenna of Body Louse, Under SEM 97

8 Campaniform Sensillae on the Second
Antennal Segment, Demonstrating Their
High Birenfringency, Similar to the
Hair Socket Between Them. . 97

9 Same View as Plate 8, but Under Nomarski
Differential Interference Contrast. 97

10 Internal Components of the Second
Antennal Segment. ... ..... 97

11 Double Chordotonal Organ on the Second
Antennal Segment. ... .. 97



Plate Page

12 Single Chordotonal Organ on the Second
Antennal Segment. . 97

13 Tuft Organ on Fifth Segment of Antenna
of Adult Body Louse . .. 110

14 Abnormal Tuft Organ on Fifth Antennal
Segment . .. 110

15 Pore Organ on Fifth Segment of Antenna. .. 110

16 Cross Section of Tuft Organ on the Fifth
Segment . . .. 110

17 Cross Section of Tuft on the Fifth
Segment . . 110

18 Cross Section Through Pore Organ on the
Fifth Segment, OsO4 Fixation. 110

19 Antenna of 3rd Instar Larva of Body Louse
Undergoing Molting. . 110

20 Abnormal Louse with 2 Tufts Found on the
Fourth Segment. .. . 110

21 Distal Three Segments of the Antenna of
lst Instar Larva. . 115

22 Tip of the Fifth Segment of Body Lice
Antenna Showing How the Peg Sensillae
Give the Impression of Thin-Walled
Sensors . . 115

23 Tip of Antenna of Body Lice 115

24 Longitudinal Thick Section of Fifth
Segment of Body Lice Antenna Showing
Cell Bodies Underlying the Peg Organs 115

25 Highly Magnified Pointed Seta from Adult
Lice Antenna ... .. 117


Plate Page

26 Cross Section of a Pointed Seta from
Adult Body Lice . .. 117

27 Oblique Section of a Pointed Seta Through
Basal Spot Area . .. 117

28 Cross Section of Pointed Seta .. 117

29 Cross Section of Pointed Seta 117

30 Cross Section of Pointed Seta .. 117

31 Ultra-Thin Section of a Group of 3 Neuron
Cells . . 123

32 Section Through Ciliary Region of Nerve
Cells Innervating the Peg Sensilla. 123

33 Section of Dendrites Bundle Beyond the
Ciliary Region. . 123

34 Section of a 2-Dendrite Bundle of a Peg
Sensor Cells. . 123

35 Cross Section Through the Tip of Antenna
of Body Louse . .. 125

36 Same as Cross Section in Plate 35, but
Distally to It. . 125

37 Longitudinal and Somewhat Oblique Section
Through the Base of a Blunt Seta. 129

38 Longitudinal Section of a Peg Sensor. 129

39 Section Through Bundle of 2 Dendrites
Prior to Entering a Pointed Seta. 129

40 Cross Section Through Peg Sensors 131

41 Cross Section of Blunt Setae in the
Proximity and Proximal to the Basal Spot. 131



Plate Page

42 Cross Section of Blunt Setae in the
Proximity and Proximal to the Basal Spot. .131

43 Cross Section of Same Sensor as in Plate
41, but Through the Basal Spot. 133

44 Cross Section of Same Sensor as in Plate
42, but Nearer to the Basal Spot. 133

45 Cross Section of Blunt Sensor, Distad to
the Basal Spot. . 135

46 SEM View of Nipple-Like Structure at the
Tip of the Blunt Setae. . 135

47 Longitudinal Section of the Nipple-Like
Tip of a Blunt Seta. . ... 135

48 Different Aspects of OsO4 Treated and
Sonicated Antennae of Body Lice 138

49 Different Aspects of Os04 Treated and
Sonicated Antennae of Body Lice 138

50 Different Aspects of Os4 Treated and
Sonicated Antennae of Body Lice 138

51 Antenna of 3rd Instar Larva Molting
into Adult. . 138


Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy



Alberto Bolivar Broce

August, 1971

Chairman: Dr. H. L. Cromroy
Major Department: Entomology

Detection of blackbody infrared radiation by the body

louse, Pediculus humanus humanus, L., was demonstrated.

Detection was studied using a good blackbody irradiator

(black paint) and a poor one (aluminum foil), both having

the same surface temperature. Detection and response were

shown by the differential aggregation of lice near the

blackbody irradiator. Change in lice activity due to

infrared stimulation was quantified by using the CO2 output

of the lice as an index of activity. No response was

obtained from stimulation by human skin gaseous emanations.

Lice were shown to detect infrared independent of the

convective heat arising from the host (blackbody irradia-


The body louse antenna was described in detail using

light microscopy and scanning and transmission electron

microscopy. The components of the propioceptive system of


the antenna were studied and their functions discussed. The

tuft and pore organs were described and a survey of speci-

mens from different laboratory colonies and from different

parts of the world showed no variation in their sensor

complement. The pointed and blunt setae on the tip of the

antenna were found to lack permeable areas. Few and narrow

pores were found on the walls of the pointed peg sensors,

but none on the blunt ones. The presence of a basal spot,

the absence of flask-shaped pores, the lack of dendrite

branching and the absence of cuticular sheath on the peg

prevent classifying these sensors as any described type of

sensillae. These observations cast doubt on the claimed

chemoreceptive function of these sensillae.

Evidence was presented to demonstrate that microtubule

multiplication inside the dendrite takes place by the

division, splitting and separation of the microtubules.




The behavior of the body louse, Pediculus humanus

humanusL., has been studied extensively, especially its

response to moisture, light, odors, surface texture and

temperature. Response to blackbody infrared radiation has

been studied extensively; however, it continues to be an

area of research most controversial and confusing. The

controversy has centered mainly on whether or not the louse

reacts directly to the infrared radiation or to the con-

vective warm air.

Previous research on louse response to blackbody

radiation has measured locomotive patterns solely. Because

of the inherent difficulty of quantifying results, using

this method, studies used few individuals. Most studies

have been of "tracks" of single lice. They have been mainly

done under the influence and interaction of several en-

vironmental factors at a time, due to the difficulty of

their isolation.

Behavioral studies of lice have been accompanied by


morphological descriptions of their sensory apparatus and

attempts at designation of functions. Some of this work has

been based on inferences made from the modification of

behavior after antennectomy.

With the use of new techniques and light microscopes

with higher resolving power, and of the newer electronic

microscopes, transmission and scanning, a more detailed

study of the antennal sensors can be performed. The study

of sensors with these techniques has resulted in great

advances. Studies of the ultrastructure of sensors usually

provide sufficient information to permit assigning a func-

tion to a given sensor, with a high degree of confidence.

However, new sensors are continually being found that do not

fit any previous morphological-functional classification.

This investigation was undertaken to elucidate the

problem of detection of blackbody infrared radiation by one-

day-starved adult body lice. A second part of this research

was a morphological study of the sensors on the louse an-

tennae with emphasis on the so-called thin-walled sensillae

on the fifth and terminal segment. These investigations

were conducted mainly at the Insect Attractants, Behavior,

and Basic Biology Research Laboratory, but also at the

Insects Affecting Man and Animals Research Laboratory,

ARS, USDA, at Gainesville, Florida.



Reactions to blackbody IR radiation

Insect reactions to temperature are a well-documented

subject (Bursell, 1964). This environmental factor has been

usually presented to the insects as either floor or air

temperature. The resultant response has generally been due

to the interaction between temperature and moisture; how-

ever, there are responses to temperature as such which have

been demonstrated for several species (Bursell, 1964).

Reactions of blood-sucking insects to the host "warmth"

havealso occupied the attention of innumerable investi-

gators. A host animal, such as a homoiotherm, dissipates

heat in the following ways: water evaporation (respiration,

sweat), conductive and convective heat, and as blackbody

infrared radiation (hereafter abbreviated blackbody IR

radiation). It is not illogical to conjecture that blood-

sucking insects use one of these forms of heat loss as a

token stimulus for host detection and, ultimately, orienta-

tion. It has been demonstrated that several species of


snakes use blackbody IR radiation for host detection (Noble

and Schmidt, 1937), and that the eye of slugs (Mollusca,

Gastropoda) responds to blackbody IR radiation (Newell and

Newell, 1968). It was .also demonstrated in several instances

that insects detect other forms of IR radiation, i.e., IR

from other sources. Callahan (1965, 1967) has proposed that

certain insect sensillae act as dielectric antenna and

therefore are tuned to discrete IR frequencies given off by

molecules. Bruce's (1969) research with the spiny rat mite,

Laelaps echidnida, Berlese, supports this theory. Recent

research by Levengood and Eldumiati (1971) on moth attrac-

tion by far IR lasers also supports these theories. Evans

(1964, 1966) showed that buprestid beetles of the genus

Melanophila can detect forest fires several kilometers away

by the use of the IR radiation produced by these fires.

To demonstrate that insects do use the blackbody

radiation from their warm-blooded hosts as a stimulus has

been most difficult, confusing and, in some instances,

frustrating to entomologists. The problem encountered by

any investigator studying IR as a stimulus for host detec-

tion has been of the same nature as the one met by physi-

cists working on this region of the electromagnetic spec-

trum, that is, the low energy of the radiations (Callahan,

1967). The large number of failures, misinterpretations and


contradictory results obtained from studies on this area are

due to the lack of understanding of the physics of this

region and/or lack of proper or efficient equipment for

defining properties or conditions encountered when trying

to measure or reproduce IR radiation. Quite often the

problem stems from failure to separate the basic components

of heat, i.e., convection, conduction and radiation. Con-

sequently, many authors talk about the host's "warmth,"

without separating these components.

Mosquitoes' response to the host's "warmth" has been a

popular subject among mosquito specialists. Parker (1948),

working with Aedes aeqrvti, L., concluded that this mosquito

is not attracted by the host's "warmth." Peterson and

Brown (1951) carried out a series of experiments with the

same mosquito, using billiard balls at different tempera-

.* tures. From these experiments they concluded that the

balls' attractiveness increased as they were heated to

110 F, but a 130 F ball was less attractive than one at

110 F. I believe this implies good temperature discrimina-

tion. When the mosquitoes were separated from the balls by

both a KRS-5 filter (transparent in the 25-40 pm region) and

at a distance of about 10 cm there was no attraction. These

authors concluded that convective heat was the factor which

made the warm objects attractive to mosquitoes. However,

Magnum and Callahan (1968) showed that this same mosquito

was attracted to a source of IR radiation, or even to the

radiation reflected from an aluminum sheet (known as a good

IR reflector).

Bedbug (Cimex lectularius, L.) behavior, as studied by

Rivnay (1932), demonstrated that "heat is an important factor

in stimulating bed bugs to obtain food." This author also

demonstrated that the bugs could detect the heat from a hand

at a distance of 4 cm, and that they were repelled when the

temperature was too high (43 C). Aboul-Nasr and Erakey

(1967) working with the same bug concluded similarly, and

believed that convective heat was the important factor.

Also, they concluded that the orientation of this insect to

heat was mainly achieved by klinotaxis and klinokinesis.

Fraenkel and Gunn (1961) defined klinokinesis as: "Fre-

quency or amount of turning per unit time dependent on

intensity of stimulation's and klinotaxis as: "Attainment

of orientation indirect, by interruption of regularly

alternating lateral deviations of part or whole of body, by

comparison of intensities of stimulation which are succes-

sive in time."

Wigglesworth and Gillett (1934) found that Rhodnius

prolixus,Stal was attracted to its host by the warmth dif-

fusing from it. Blinded specimens could go straight to a

test tube with warm water 3-4 cm away, but antennaless

specimens didn't show this reaction. They believed that the

thermal sensors were located chiefly in he antenna, but

could not locate them.

Reports on behavior of anoplurans to warmth included

a number of scattered observations and experiments, and a

few extensive studies. Frickhinger (1916) (as quoted by

Rivnay, 1932) stated that the body louse had a sense of heat

(warmesinn). Howlett (1917) made some interesting observa-

tions on head and body lice and their temperature reactions.

He described the change in locomotive activity, both quan-

titatively and qualitatively, of lice stimulated by the

radiant heat from a tube at 35 C. Crab lice, Phthirus

pubis L., as tested with the warm tube (also called a

"finger"), presented a reaction similar to body lice.

Martini(1918) reported that body lice aggregated under a

source of radiant heat, even if it meant their moving from

the warmer to the cooler part of a temperature gradient

(quoted in Fraenkel and Gunn, 1961).

The next important work in this area was written by

Homp in 1938. This study illuminated many of the behavioral

patterns of lice, but at the same time produced a great

number of contradictory conclusions. She studied the

temperature changes of the arena floor, the air and the lice

when a warm "finger" was brought close (in some cases she

worked with temperatures not usually encountered by the

lice, such as 49 C). It was known that lice would follow

a warm "finger." Homp blinded several lice and they still

would follow the "finger," but when it was quickly with-

drawn, the lice would abandon their orientation toward the

"finger." Homp concluded that lice did not respond to

radiant heat. This author concluded that the movement of

lice towards a warm "finger" was consistent with klinotaxis.

The Wigglesworth (1941) paper on the sensory physiology

of body lice is a classic on the study of sensory physiology

by means other than electrophysiology. In this work he

studied reactions of lice to temperature, humidity, smell,

contact and light, and included a morphological study of the

lice sensors. He concluded that the mechanism of orienta-

tion to temperature consisted of an increase of random

turning movements, in other words, klinokinesis. He stated

that "there is no evidence that the louse is 'attracted' by

a favourable stimulus, although it may show a directed

orientation where there is a steep gradient of stimuli."

In order to test the ability of lice to detect IR

radiation he performed the following experiment:

a circular tin, 9 cm in diameter, was lined
with aluminum foil, and on one half of the wall
this was covered with thin cellophane gummed to

the surface. The thin cellophane covering makes
little difference to the conduction of heat and
consequently to the gradient of air temperature
from the walls to the centre of the arena. But
it makes a great difference to the radiant heat.
The emissivity of the aluminum covered by cello-
phane is almost equal to that of a dull black sur-
face; the emissivity of the aluminum alone is
only about 5% of this.

The walls of the arena were heated equally or differ-

ently. Using this arrangement, he released lice on the

center of the arena. He measured also the temperature of

the air adjacent to the walls. All of these experiments

were conducted under good light conditions. He recorded

the "tracks" of lice leaving the cluster at the center of

the arena and moving toward the walls. He did not find any

difference between the lice orientation toward the cello-

phane (good irradiator) and the aluminum (poor irradiator)

surfaces. Unfortunately, he did not record the path of the

lice after they had reached the walls. A louse walks in the

same orientation which it had when dropped on the arena

floor. It is not until the louse is close to a warm body

that it moves directionally (Homp, 1938; Weber, 1929).

Wigglesworth may have been able to obtain more information

from these observations. His final conclusion was that "the

response is always to air temperature, there is no response

to radiant heat from objects at 20-45 C." Homp (1938) and

Wigglesworth (1941) observed that lice deprived of their


antennae would come very close to a hot object, while normal

lice would avoid objects at 40 C; that is, the antenna

possesses sensors that are sensitive to high temperatures.

Wigglesworth (1941) showed that antennaless lice could

discriminate different temperatures only when this differ-

ence was great, i.e., between 20 and 30 C.

The response of blood-sucking insects to heat has been

measured with different techniques. One of the most common

has been by observing some type of behavior associated with

feeding. Hopkins (1964) used the "thrusting movement of the

extended proboscis" of the stable fly (Stomoxys calcitrans,

L.); similar responses were used by Rivnay (1932) with the

bedbug and Wigglesworth and Gillett (1934) with Rhodnius.

Other forms of behavior associated with feeding have been

used, such as questing of sheep ticks, Ixodes ricinus, L.

(Lees, 1948) and spiny rat mites, Laelaps echidnida (Bruce,

1969). Aboul-Nasr and Erakey. (1967) used the awakening

from akinesis of bedbugs as a positive response to


Another form of monitoring response behavior to heat

has been recording the number of insects reaching the

stimulus area, such as the work with mosquitoes (Parker,

1948; Peterson and Brown, 1951; Magnum and Callahan, 1968).

Berry and Kunze (1970) quantified the response of stable

flies to blackbody IR radiation by means of their flight

activity, an indirect method. Turner and Charity (1971)

determined activities of moths (a non-blood-sucking insect)

by continuously monitoring their carbon dioxide output.

A widely used method has been recording the "tracks" of

the insects and analyzing them. This method has the ad-

vantage of providing insight into the type of orientation,

but at the same time it suffers from many inherent problems.

It is difficult to quantify and has to be conducted with one

or a few individuals at a time. In addition, it has to be

performed under well-lighted conditions and this is an un-

natural condition to many blood-sucking insects. Also, the

investigator has to be in close proximity to the experiment

to record the response, and it is difficult to exclude his

own radiation and other dissipating factors (i.e., odor,

CO2, breath) from influencing the test insect.

Morphology of antenna sensors

The varied array of sensors on insect antennae is a

source of speculation as regards their functions and has

been a challenge to study since the early days of experi-

mental biology. Experiments to test the hypothesis that the

antennal sensors are involved in olfaction were conducted

as early as 1734 (Dethier, 1954). Electrophysiological

techniques have proven the hypothesis that olfactory sensors

are located principally on the antenna. These techniques

have also shown that there are other types of antennal

sensors with functions other than olfaction, i.e., tempera-

ture, sound, mechanoreception.

Knowledge of the ultrastructure of insect sensillae has

increased greatly in the last decade. These rapid advances

can be linked to the popularization of the electron micro-

scope and improvement of sample preparation techniques.

Fixation and sectioning of sensory structures on insect

antennae present special problems correlated with the hard

cuticle and small diameter (Slifer, 1968). The morphology

of the body louse antennae was studied first by Keilin and

Nuttall in 1930. These authors reported that the main

structures on the antenna of the first stage larva "examined

in vivo" showed upon clearing the following structures:

"two biscolopal and one monoscolopal chordotonal organ" (on

the second segment), "muscles on the basal segment, antennal

nerve divided into two branches, sensory papillae with

their ganglia" (on the tip of the fifth segment), and

"sensory tuft of 4 hairs with tube penetrating into sensory

ganglion" (on the fourth segment).

Wigglesworth (1941) described in greater details the

antenna of the body louse, but in this case it was of the

adult louse. According to this author, the body louse an-

tenna consists of five segments bearing three types of


Peg organs. There are nine or ten on each antenna:
three sharply pointed, lying dorso-lateral and six,
or usually seven, of varied length, with rounded
tips, lying medial and ventral. In section they are
seen to be exceedingly thin-walled. Below each is
an elongated group of about six sense cells, the
distal processes of which unite to form a filament
that can be traced into the cavity of the peg.
Tuft organs. In the adult louse there are three tuft
organs on the dorso-lateral aspect of the fifth seg-
ment and one at the tip of the fourth segment or its
outer side. Each consists of a minute cone.arising
from the floor of a saucer-shaped depression. At the
apex of the cone there is a tuft of four tiny delicate
hairs which stain weakly with haematoxylin. These
hairs appear to arise from a delicate membrane.
Below this is a little oval cavity through which runs
a deeply staining rod or filament attached at the
point where the four hairs unite. A curved tubular
thread connects this rod with a group of five or
six sense cells.
Tactile hairs. These are of the usual type and
consist of a slender bristle arising from a socket
below which are trichogen and tormogen cells and a
single sense cell with axon fibre. They vary some-
what in number, but there are usually 5-7 on segment
1, 8-10 on segment 2, 5-7 on segment 3, 3-4 on seg-
ment 4, 3-4 on segment 5.
Scolopidial organs. In segment 2 there are Johnston's
organ and some chordotonal organs, which will not be
described in detail.

The two previous descriptions disagree on the number of

tuft organs on the antenna. This difference is the result

of the studying of immature and adult forms of the same

species. Miller (1969) reported a discrepancy between his

study and that of Wigglesworth's on the number of tuft


organs on the adult body louse antenna. According to Miller,

there was only one organ on the fifth segment and another on

the fourth. However, he found two pore organs in the loca-

tions where Wigglesworth had reported the tufts. Miller

extended this study to several races of body lice from North

America and has obtained the same results (personal communi-

cation, 1970).

The morphology of the tuft organs on the antenna of the

body louse have not been studied in detail. Very few other

tuft organs have been studied. Hafez (1950) described two

types of sense organs from the mesothorax of the house fly

(Musca domestic, L.) larva, and he believed they were

hygroreceptors. One type is in the form of a "minute brown

circular structure about 10 p in diameter"; it possesses a

thin dome-like cuticular covering. The second type con-

sists of "three minute hairs arising from the floor of a

slight depression of the cuticle. Below these hairs is a

small oval cavity through which extends a somewhat deeply

staining rod." These hairs were about 6 pm in length

(Hafez, 1950). Roth and Willis (1951) described some tufted

basiconic sensillae, bearing a varied number of prongs 5-15

pm in length, from the antennae of several species of Tri-

bolium. They concluded these sensors were hygroreceptors.

It is interesting to notice the similarity between

these two tufted-sensors and the ones on the body louse.

The major difference is their dimensions; in Pediculus, these

hairs are approximately 2-3 pm in length (Miller, 1969).

Wigglesworth (1941) stated that the tuft organs on the body

louse are hygroreceptors: the same function as in the

species of Tribolium (Roth and Willis, 1951). However,

Miller has recently indicated (personal communication,

1970) that he has evidence that these tuft organs are not

moisture receptors of the louse, as reported by Wiggles-

worth (1941).

Wigglesworth (1941) coated the peg organs on the apex

of the fifth segment and concluded that these "exceedingly

thin-walled sensors" were involved in olfaction. These pegs

have often been cited in the literature as excellent examples

of thin-walled sensillae (Slifer, 1968; Schneider, 1964;

Dethier, 1954). Schneider (1964) made reference to the

Wigglesworth experiment as one of the few cases in which "it

was possible to identify olfactory sensilla basiconica on

antenna" with a sealing method. However, Chapman (1969)

criticized this methodology by stating that "the identifica-

tion of olfactory receptors is often uncertain because it is

based only on the results of ablation experiments."

Classification of antennal sensors, as to sensory mode,

has been based mainly on their morphology. A function can

be assigned to a sensor, based on its morphology, especially

its ultrastructure. Such classification has often been

demonstrated to be correct by electrophysiological studies.

The peg organs at the tip of the body louse antennae

have been classified as basiconic sensillae. Schneider

(1964) described basiconic sensillae as follows: "omni-

present trichoid sensilla without any specialized basal

membrane. If present together with sensilla trichodea on an

antenna, they are relatively shorter and usually have a thin-

ner wall. From one to several nerve fibres have been ob-

served in connection with these organs." Sinoir (1969)

described them as being generally small or very short

bristles of conic shape, with no articulation at thebase

or mechanoreceptive structures, and possessing several sense

cells under the peg.

Previous to the study of basiconic sensillae with the

transmission electron microscope, it was discovered that

these pegs stained with certain dyes. The dyes penetrated

the pegs throughout the surface of some of them, but, in

others, only through the distal tip (Slifer, 1954a).

Slifer, Prestage and Beams (1957) confirmed this earlier

observation with the use of the transmission electron

microscope. These authors found that those basiconic sen-

sillae staining through the tip had an opening (hole) at the

tip through which the distal processes of the sensory cells

were exposed. Later, these same authors reported that the

surface of the short, thin-walled basiconic pegs on the

antenna of grasshoppers was perforated by a large number

of pores between 0.1 and 0.2 pm in diameter, through which

the distal tips of the dendrites were exposed. These were

the sensillae which stained throughout their surface

(Slifer, Prestage and Beams, 1959). These two types of

basiconic sensillae are referred to as thick-walled (with

an opening at the tip) and thin-walled (with pores through-

out its surface). The classification is not based only on

the thickness of the cuticle, but on other characteristics

as well (Slifer, 1970).

A basiconic sensillum,whether thick- or thin-walled,

is innervated by one or more bipolar nerve cells which send

dendrites into the peg and axons to join the antenna nerve

(Slifer, 1970). When the dendrite leaves the cell body, it

assumes certain peculiar characteristics. Near the nucleus,

it narrowsdown and takes the form of a cilium with nine

pairs of peripheral double fibrils (doublets), but lacking

a central pair. A basal body with a periodic structure

arises from the cilium toward the nucleus. The cross

section of this basal body indicates that it is composed of

nine triple fibrils (triplets). When they enter the ciliary


region they become the doublets. The doublets of the cili-

ary region separate and enter the dendrite, which travels

towards the peg; here the fibrils become indistinguishable

microtubules (Slifer, 1970; Slifer and Sekhon, 1969).

Slifer and Sekhon (1969) presented evidence that the

microtubules were a continuation of the fibrils; they usually

split and so their number increased above 18. Microtubules

in the dendrites have been usually found in numbers close

to 18, or in multiples such as 36, 72, etc. The variation

in number may be a result of the microtubules not all

dividing or doing so at different levels (Slifer, 1970).

The trichogen cell which surrounds the sense cells usually

forms vacuoles around the basal and ciliary regions of the

dendrite. The tormogen cell which lies closer to the

cuticle under the peg also forms some vacuoles around the

dendrite (Moeck, 1968). The dendrites are surrounded by a

cuticular sheath from the point where the fibrils become

microtubules (Slifer, 1970). From this point toward the peg

is where the major difference exists between the thick- and

thin-walled sensillae, i.e., the ultrastructure of the peg.

There are several excellent review papers on the ultra-

structure of thin-walled sensillae for they have been

studied more than any other sensor on the antenna. There-

fore, there is no need to discuss them in detail. The

following description of these sensors was synthesized from

these review papers (Slifer, 1968, 1970; Sinoir, 1969;

Schneider, 1969).

The surface of the thin-walled sensillum is perforated

by a great number of pores which open to a spherical

chamber; from this chamber tubules penetrate the cuticle

toward the hair lumen and are in close proximity to the

dendrites. This type of sensillum may be innervated by one

or as many as 60 dendrites. There is a cuticular sheath

surrounding the dendrites and it is invaginated from a spot

at the base of the peg (basal spot). During molting, the

sheath is shed through this hole. The dendrites cross the

cuticular sheath near its distal end and enter the lumen of

the peg. Branching may occur near the base or at different

levels of the peg; and may produce small dendrites with many

microtubules or as few as one.

Crystal violet, methylene blue and silver compounds

have been the most commonly used chemicals to detect the

presence of holes on thin-walled sensors with the use of the

light microscope. These compounds also penetrate the basal

spot on the peg. The pores have been studied with the

transmission electron microscope in several species. Thin-

walled sensillae have been demonstrated by electrophysio-

logical techniques to be the main olfactory organs in



Thick-walled basiconic sensillae possess a lumen.filled

with few dendrites, usually close to five. In some cases,

it has a double lumen, one portion being occupied by the

dendrites (Slifer, 1970; Foelix, 1970). The presence of a

lumen throughout the bristle is the main characteristic that

distinguishes a thick-walled basiconic from a mechanorecep-

tive hair (Sinoir, 1969). A thick-walled sensillum has a

single opening at its tip, through which the distal ends of

the dendrites are exposed and these dendrites may even ex-

tend slightly beyond the tip (Slifer, 1970). Slifer (1967)

found that thick-walled sensillae in earwigs (Forficla

auricularia, L.) had a broad pad-like tip which stained

deeply with crystal violet.

A tubular sheath of cuticle is invaginated from the

open tip of the peg which passes down the peg lumen. This

cuticular sheathnarrows at the base of the peg, and then

widens below the base (Slifer, 1961). Slifer, Prestage and

Beams (1957) showed that during molting the cuticular sheath

is pulled out through the open tip and shed in this fashion.

The occurrence of an open tip has been demonstrated by

several techniques such as dye penetration using crystal

violet (Slifer, 1960), methylene blue (Slifer et al., 1959;

Foelix, 1970) and different silver preparations, such as

silver nitrate (Slifer et al., 1957), the scanning electron

microscope (Foelix, 1970), and the transmission electron

microscope (Adams et al., 1965; Sturckow et al., 1967).

Slifer, Prestage and Beams (1957) showed that when a fresh

antenna was examined on a slide with olive oil and pressure

applied to the cover slip, a drop of fluid would be forced

out through the tip and if the pressure was held long enough,

there was a crumpled membrane seen when the pressure was

released. The majority of the thick-walled sensillae de-

scribed exhibit longitudinal fluting (Moeck, 1968), longi-

tudinal surface striae (P. S. Callahan, personal communica-

tion, 1970) or oblique striation spiraling around the shaft

of the hair (Foelix, 1970).

Thick-walled sensillae had been found in many species

of insects and other arthropods (Foelix, 1970). They were

reported from different parts of the body besides the

antenna (Slifer, 1970). Slifer (1954b, 1970) demonstrated

that the thick-walled pegs on the grasshopper are the

"receptors for the common chemical sense and are stimulated

by strong repellent odors." Thick-walled sensillae have

been demonstrated to be contact chemoreceptors in several

flies, such as Phormia regina, Meigen (Dethier, 1955),

Stomoxys calcitrans (Hopkins, 1964). Foelix (1970) stated

that "an open tip is a strong argument for a chemoreceptive


Moeck (1968) described a hair sensillum from the

ambrosia beetle (Trypodendron lineatum, Oliver) as being

thick-walled, having no open tip, but having instead a few

flask-shaped holes over the surface. These holes had a

diameter of 200 A; two dendrites entered the hair lumen and

branched in its distal half.

Thurm (1964) described in detail the ultrastructure of

mechanoreceptive sensillae of the honey bee, Apis mellifera,

L. The articulated hairs are innervated by mechanoreceptive

dendrites which are attached to a tubular electron-dense

body at the base of the hair. Adams, Holbert and Forgash

(1965) found that one of the dendrites innervating the

thick-walled tarsal and labellar hairs of Stomoxys calci-

trans was attached to the hair and this could be a mechano-

receptor. It is known that similar hairs in Phormia regina

respond to mechanical as well as to chemical stimuli (Gra-

bowski and Dethier, 1954). Foelix and Axtell (1971) re-

ported that certain setae on the tarsi of the tick Amblyomma

americamum (L.) are innervated by both mechanoreceptive

dendrites ending as a tubular body at the bristle hair, and

dendrites occupying the hair lumen.

A critical review of the literature on sensor classi-

fication demonstrates the inconsistency among different

authors. For instance, Schneider (1969) considered sensillae

trichodea as being "long, thick-walled hairs or pegs."

Lewis (1971) described the trichoid sensillae on the anten-

nae of Stomoxys calcitrans as being "the largest and most

conspicuous of the antennal sensillae, curved structures

tapering to a point." They had about 500 pores on their

walls and a cuticle 0.5 to 1.0 pm thick. It appears that

recent workers consider Slifer's thick-walled sensillae to

be trichodea. Sensillae nomenclature is in such a state of

instability and so many different types and variations are

constantly being described, that many authors avoid using

any established sensillae names, and prefer using setal

maps (Foelix and Axtell, 1971) or give them names associ-

ating their gross morphology with common objects (Callahan,

1969, and personal communication, 1970).



The test insect

Body lice were obtained from the rearing facilities at

the Insects Affecting Man and Animals Research Laboratory

of the United States Department of Agriculture, Gainesville,

Florida. Rearing procedures have been published elsewhere

(Smith and Eddy, 1954). The lice were held on 2-inch square

patches of black corduroy. Black cloth was used because the

eggs and lice are more visible on the dark background. The

patches with lice were kept in stainless steel dishes and

maintained in cabinets at a relative humidity of 60 percent

or less and at about 25 C. They were fed on rabbits twice

each day, morning and afternoon. The patches were placed on

the shaved ventral side of the rabbits. After 30 minutes

the patches were rubbed against the rabbit skin and the lice

were easily picked up as they clung to the cloth.

Lice from the standard colony were used for the

behavioral experiments and for morphological studies, unless

otherwise stated. The standard colony was started in 1942


from specimens collected from humans in Washington, D. C.,

and has been maintained in the laboratory since that time.

Lice from three other experimental colonies were used for

morphological comparisons. These were: Korea, collected

in 1951 and selected for DDT resistance; Freetown, collected

in Sierra Leone in 1956 and selected for Lindane resistance;

and Burundi, collected in 1970 and selected for Malathion

resistance (M. M. Cole, personal communication, 1970)

Behavior experiments

For the behavior experiments, only adult lice were

used, 3 to 5 days after their last molt. Since sexing was

difficult, both females and males were used. Fully engorged

lice were obtained and then starved for 24 hours (+ 12 hrs.)

before using them in any experiment. No apparent physio-

logical harm from this procedure was observed. Lice can

survive without food for several days (Buxton, 1946). All

the tests were conducted in rooms at 22 C and 50 percent

relative humidity.

The behavior experiments dealt with the response and

detection of blackbody IR radiation by body lice; hence,

attempts were made in all tests to control carefully other

stimuli. Lighting effects presented many problems. Wiggles-

worth (1941) showed that lice moved toward dark.places or

dark objects, and that slight differences in the light

received from different directions elicited greater re-

sponses if the lice were exposed to a general low intensity

illumination. Therefore, the experiments were conducted in

a closed room with the lights off, except when light was

necessary. Preliminary control experiments demonstrated

that the lice were reacting to the extremely low intensity

light coming under and around the door cracks; therefore

it was necessary to tape black cloth around these areas to

completely eliminate any stray light. Obviously, running

the experiments in the dark presented many problems and

restricted gathering certain information; however, darkness

is a natural condition for the lice. Buxton (1946) criti-

cized Wigglesworth's work (1941) on lice orientation and

reaction todifferent stimuli for running them under good

illumination, because this was "an unnatural condition to

them" (to the lice).

Wigglesworth (1941) demonstrated that lice reacted to

several odors, including sweat, other lice or their ex-

creta. In order to eliminate any interaction of odor with

the response to blackbody IR radiation I had to artificially

reproduce the skin blackbody IR radiation. Human skin is

an ideal blackbody, since its emissivity approaches unity

from about 3 pm to 15 pm (Hardy, 1954, as quoted by Barnes,

1967). Mitchell, Wyndham and Hodgson (1967) quoted an

emissivity mean value of 0.997 + 0.001 for the skins

sampled. They also confirmed Hardy's statement that "the

emissivity of skin in its thermal emission band does not

depend on the skin pigment" (Hardy, 1934, as quoted by

Mitchell et al., 1967). The blackbody spectra of several

materials at 33 C and human skin were determined using an

FTS-14 interferometer (Digilab-Block Engineering, Inc.).

This is an infrared Fourier transform spectrometer which

utilizes a Michelson interferometer. Materials to be

analyzed were attached to a 1-inch square, 5-watt tape

heater (Electrofilm, Inc.) covered with aluminum foil. The

materials were heated to 33 C (surface temperature) by means

of a temperature controller (Alton Electronics Co.) which

could control the temperature within 0.25 C of the set

temperature. Surface temperature readings were made with

a thermistor digital thermometer model 501 with a scale of

hundredths of degree C (t 0.15 C accuracy, 0.05 C repeata-

bility; United Systems Corp.). Some of the materials tested

were: Aluminum foil, Plexiglas, Saran wrap cellophane

(cigarette package wrapping), black electrical tape, 3M

black paint (Velvet coating No. 101-C10, emissivity = 0.97;

Minnesota Mining and Manufacturing Co.), and rubber glove

(Surgeon's glove, grade A; Perry Rubber Co.). The blackbody


spectra of human skin, 3M black paint, rubber glove, alumi-

num foil and cellophane are shown in Figures 1, 2a, 2b, 3a

and 3b. The 3M black paint at 33 C approximated best the

human skin and it was selected to serve as "human skin" in

further tests. A temperature of 33 C was chosen as a stand-

ard human skin temperature. Mitchell et al. (1967) stated

that the skin temperature varies considerably, but it is

known to be in the region of 25-40 C; Barnes (1967) showed

that the average palm surface temperature was 32.4 C (range

29.7-34.3 C).

Straight arena experiments

The first set of experiments were run in a straight

arena to test the ability of body lice to detect blackbody

radiation and move towards the source of IR. An arena was

made with plexiglass, 24 cm X 7 cm, with 1 cm high walls.

The inner surfaces of the walls were of plexiglass which

prevented the lice from climbing. The arena floor was made

of white blotting paper, which was changed after each ex-

periment. The arena was marked every 3 cm, forming 8 com-

partments or sections. Two 1 inch square, 5-watt tape

heaters were covered with aluminum foil and were used as

blackbodies. One side of each heater was painted with the

3M black paint. Each heater temperature was adjusted

Figure 1. Infrared spectrum of human hand, in the range of
25.0 to 3.3 pm (400 to 3,000 cm1). The y-axis
represents the radiation relative intensity (RI)
and is not comparable to the other spectra.
Spectrum was obtained in a FTS-14 Interferometer
(Digilab-Block Engineering, Inc.).

25 10





Figures 2a, b. Infrared spectra of (a) black paint (Velvet
coating no. 101-C10, emissivity = 0.97; Minnesota
Mining and Manufacturing Co.) and (b) cellophane
(cigarette package wrapping), heated to a 33 C
surface temperature. Spectral range covers from
25.0 to 3.3 pm (400 to 3,000 cm-1). The y-axis
represents the radiation relative intensity (RI)
and is not comparable to the other spectra.
Spectra were obtained in a FTS -14 Interferometer
(Digilab-Block Engineering, Inc.).



S 200

5 4

3M-B P


Figures 3a, b. Infrared spectra of (a) rubber glove (Sur-
geons glove, grade A; Perry Rubber Co.) and (b)
aluminum foil, heated to a 33 C surface tempera-
ture. Spectral range covers from 25.0 to 3.3 pm
(400 to 3,000 cm-1). The y-axis represents the
radiation relative intensity (RI) and is not
comparable to the other spectra. The intensity
readout gain for the aluminum was greatly increased
over the other spectra, and the output is mainly
electronic noise amplification. Spectra were
obtained in a FTS-14 Interferometer (Digilab-
Block Engineering, Inc.)

25 10 jm 5



cm- 2000
c m


and maintained at 33 C using the temperature controller.

Even though both of the surfaces of a heater (black and

aluminum) were at 33 C, the black one irradiated more energy

as IR than the aluminum, due to the black's higher emissiv-

ity, 0.97 (manufacturer's specifications) versus 0.10

(Hemmerdinger and Hemback, 1965).

The heaters were suspended freely at each end of the

runway, 1 cm above above the arena floor. The experiments

consisted of having a blackbody radiator (hereafter called

blackbody or BB) at one end and an aluminum one (hereafter

called aluminum or Al) at the other. Fifty, one-day-starved

lice were released on the center of the arena. At the end of

3 or 5 minutes the lights were turned on and the number of

lice on each compartment was recorded. Controls were run

with both heaters off. The arena compartments were enumer-

ated or classified according to their relative position to

the blackbody. Lice on the two central sections were not

recorded, because it was hypothesized that a louse found on

these sections had not reacted to the offered stimuli. The

compartment closest to the blackbody was weighted with a

factor of +3, the next ones, +2 and +1. The section closest

to the aluminum was given a factor of -3, and the following,

-2 and -1, respectively. This was done because a louse

recorded at a 3 position is weighted statistically more than

one at 2 or 1; that is, a louse that had moved closer to a

heater should be considered more than one at a 2 *or 1

position. This method of weighting the data according to

the position of the specimen has been used with data from

several types of insect olfactometers (M. S. Mayer, personal

communication, 1970). It was necessary to normalize the

recorded values on base 100, because the number of responding

lice in each experiment varied considerably. This normaliza-

tion was carried on prior to weighting the data.

Round arena experiments

As previously stated, Wigglesworth (1941) believed that

lice did not detect IR radiation; the response to the

"warmth" of an object was due to the heated air, i.e., the

convective heat. In order to determine whether lice could

detect IR when convective heat was eliminated, the following

experiment was conducted.

A circular arena with an. 8 cm radius was made out of a

flat plastic dish with a rim of 0.4 cm to prevent the lice

from escaping. The arena was positioned on the center of

the top of a 30 X 30 X 4 cm plexiglass box. Two circles,

8.0 and 9.0 cm radii, were traced on the box top and a

maximum number of 1.5 mm holes drilled between them. A 60 X

2.5 cm tape heater was lined with aluminum foil and attached

to the inner part of a plexiglass tube of 2.5 cm high and

9.25 cm inside radius. This ring was positioned on the box

top (see Figures 4a, b, and c). The intention was to blow

air into the box and force the air to escape through the

small holes; the plexiglass tube (with the tape heater) and

the arena walls would serve as channeling walls for the air.

In this manner, a curtain of fast moving air was formed

between the heater and the arena, eliminating the effect of

convective heat. Compressed air from the laboratory line

was used. It was cleaned and dried using the following

attachments: 1) a pressure valve; 2) a water trap; and 3)

a cylinder of glass wool followed by a second cylinder with

activated charcoal, and finally calcium sulfate (Drierite.

The flow of air was maintained constant at 12,000 cc min-,

as measured with a glass flowrator (Fischer and Porter, Co.).

The air was introduced through the bottom of the box. The

box was sized to prevent turbulence that might cause dif-

ferential flow rates through the holes on the box top.

The tape heater was divided in 8 equal sections; half

of them were painted with the 3M black paint and the rest

left with plain aluminum (see Figures 4a and b). Thus,

blackbody opposed blackbody, and aluminum opposed aluminum.

This prevented the aluminum, an efficient reflector (see

Figures 5a, b, and c), from reflecting the IR from the

Figures 4a, b, c. Round arena apparatus designed to study
the lice detection of infrared radiation, but
eliminating the convective heat arising from the
blackbody and aluminum radiators (r). A vertical
laminar air flow was provided between the radi-
ators and the arena. A constant air flow of
12,000 cc min-1 was supplied to the plexiglass
box (b) through a tube (t). The arena (a) was
positioned over the box and it was surrounded by
the radiators. Air flowed from the box through
holes drilled around (h) the arena. Apparatus
drawings are not at scale.


a r r

b b .. .

.1 .

Figures 5a, b, c. Infrared spectra of infrared radiation (a)
reflected at a 900 angle from (b) aluminum and
(c) black paint (Velvet coating no. 101-C10,
emissivity = 0.97; Minnesota Mining and Manufac-
turing Co.), demonstrating the good reflectivity
of aluminum and the poor one of black paint
(reflectivity is inversely proportional to emis-
sivity). Blackbody infrared source was a black-
body radiator (black paint) at 38 C surface
temperature. The high temperature was used to
provide enough energy for analysis after reflec-
tion. Spectral range covers from 25.0 to 3.3 ju
(400 to 3,000 cm-1). The y-axis represents the
radiation relative intensity (RI). The intensity
readout gain for the blackbody was greatly in-
creased over the other spectra. Spectra were
obtained in a FTS-14 Interferometer (Digilab-
Block Engineering, Inc.).


BB 380C




black surfaces (blackbodies). The tape heater was main-

tained at 33 C (surface temperature) using the temperature

controller. The arena floor was made out of white blotting

paper with a 7.5 cm radius so that the paper was 0.5 cm from

the arena wall. The paper was divided (with pencil lines)

into 8 equal partitions (pie wedges) with 4 diameter lines;

a 5.5 cm radius circle was also traced on the paper. The

paper was changed after each experiment. One hundred, one-

day-starved lice were released in the dark on the center of

the arena. After 5 minutes, the lights were turned on and

the number of lice on each compartment counted with a hand

counter. Only those lice that reached the 5.5 cm radius

circle were recorded as responding. This outer circle

represented 46 percent of the area of the arena, and was

3.75 cm from the heater surface.

This experiment posed the following problem: Did the

lice discriminate between the two heated surfaces (black or

aluminum) after they reached the arena border, or did they

orient themselves before reaching that point? In order to

investigate the above, the arena floor was modified in the

following manner: circles of varied radii, 2.0, 4.5 and

6.0 cm were traced on the paper arena. The arena was again

divided into 8 equal compartments by the 4 diameter lines.

It was then cut along the circle (i.e., the 6.0 cm radius)

but leaving a 1 cm wide strip along the diameter lines.

This way 8 strips of paper extended from the arena, and each

pointed toward a different section of the tape heater

(Figure 6). The same procedure was followed with the 4.5

and 2.0 cm circles. The reason for the different strip-

lengths was to determine how far away lice could detect and

orient to the blackbodies. One cm square pieces of black

corduroy were attached to the end of each strip and this

served as a "trap" for the lice. Lice prefer rougher

surface, hence, they prefer cloth over paper. These patches

prevented the lice from moving away from the strips once

they had made their choice. One hundred lice were released

on the center and after 5 minutes the lice on the patches

were counted as responding lice. The values obtained were

normalized to base 100 because not all the lice responded.

Each test was replicated five times and the number of lice

per compartment was recorded individually and analyzed by

a "t" test.

CO2 monitoring experiments

The response of body lice to blackbody radiation was

quantified by monitoring constantly the CO output before

and during IR stimulation. In this indirect method, it was

assumed that CO2 output was proportional to locomotive

Figure 6.

A schematic diagram of the 2.5 cm strip arena.
It illustrates the arrangement of the strips and
the corduroy traps, in relation to the whole arena
and the heaters. Similar format was followed in
making the 4.75 and the 7.5 cm strip arena.
Schematic diagram is drawn on a 1:1 scale.


SPaper Arena



Nots il ... e t er


activity. It had been observed that akinetic lice began

moving when a warm object was brought close to them (Homp,

1938; Howlett, 1917). Undoubtedly, this activity was diffi-

cult to measure and quantify. Turner and Charity (1971)

described a method for measuring moth activity by monitoring

the CO2 output.

The lice were confined in a 4.0 cm high chamber made

from a 3.8 cm diameter plexiglass tubing, and mounted on a

8 cm square plexiglass plate. Two 0.5 cm diameter and 3 cm

long plexiglass tubes were attached 1.0 cm high on opposing

sides of the chamber for the input and output of air. The

chamber top was a removable 8 cm square plexiglass plate.

Two 10 KA, 2-watt resistors were suspended horizontally

from the chamber top; when the top was positioned, these

resistors were 2 cm from the arena floor. The resistors

were 0.8 cm apart and each connected to a different tem-

perature controller set at 33 C surface temperature (see

Figure 7). Both resistors were covered with aluminum foil,

and one of them painted with the 3M black paint to serve as

a blackbody radiator. A thermistor, within the tip of a

hypodermic needle, was vertically inserted between the ends

of the resistor and the chamber top and positioned to have

its tip equidistant from both.resistors and 0.3 cm above

the chamber floor. This thermistor was positioned so to


Figure 7.

CO2 chamber for monitoring lice activity during
stimulationwith blackbody infrared radiation.
The chamber walls were made of plexiglass and
the chamber floor of blotting paper. Each
radiator was independently connected to a
temperature controller, and the temperature was
monitored using the temperature probe and a
digital thermometer. The chamber was connected
to a compressed air line (air in) and to the CO2
analizer (air out). Schematic diagram not
drawn at scale.




measure the air temperature. It was connected to a digital


The chamber floor was made of blotting paper. The

chamber was connected with TygoAtubing to a CO2 analizer

(IR analizer, LIRA model 200, Mine Safety Appliances, Co.).

Two lines supplied air from a compressed air tank, at a

constant rate, to the analizer. One of the two lines was

connected directly to the analizer and served as a reference,

the air from the other line passed through the chamber with

the insects. The difference in the concentration of CO2

between the two lines could be read directly in parts per

million (ppm) from a metered scale or plotted on a time

basis. CO2 concentration was recorded by a Leeds and

Northrup, Speedomax strip-chart recorder (see Figure 8a).

Preliminary tests indicated that as few as 10 akinetic lice

gave a reading of about 5 ppm. It was decided that 50 lice

would give more meaningful and statistically valid

readings. Preliminary tests with 50 lice indicated that

the CO2 concentration increased between 30 and 60 percent

when only 20 lice were walking, upon stimulation by the

blackbody radiation; this was observed under well-lighted

conditions, but the rest of the experiments were conducted

in total darkness by placing the chamber inside a closed

0.60 X 0.60 X 0.75 m box. This box was kept at a tempera-

Figures 8a, b, c. CO2 monitoring flow chart. (a) Lice were
held in the same chamber with the heaters. Air
flowed from the chamber to the CO2 analizer (A).
The output from the analizer was recorded on a
strip chart recorder (B). (b) Control experiments
in which the lice were held in a chamber following
the heaters chamber. (c) Control experiments in
which the lice were held in a chamber preceding
the heaters chamber. A further control experi-
mental setup (not illustrated) consisted of
removing the lice altogether from the system.

Iff T Almrinum

ture of about 26 C by way of an air heater connected to a

temperature controller. Air flow to the lice chamber was

calibrated to 50 cc min-I and the line air kept at a

temperature close to 26 C.

During any given test, the lice were introduced into

the chamber connected to the sample line. The box was

closed and 30 minutes were allowed for the lice to go into

akinesis, before any test was conducted. The heaters were

turned on and off, one at a time according to the test. In

one series of tests, the blackbody was turned on for 2.5

minutes, off for 2.5 minutes, on for 2.5 minutes, and so on.

In another series, this procedure was repeated with the

aluminum heater. In another, the blackbody and aluminum

heaters were alternated after an off period. Several con-

trol experiments were run, as follows: a) Lice removed

from the chamber, b) lice in a container next on the line

from the heater's chamber (heaters on) (see Figure 8b),

c) lice in a container preceding the heater's chamber

(heaters on) (see Figure 8c). Variation in CO2 output over

a long period of time was determined by recording the CO2

output every 5 minutes for 6 hours.

In order to test the effect of odors and CO2 emanating

from human skin, air was blown through a chamber attached

to the arm of volunteers (K. F. and M. S.). Air drawn

through this chamber was introduced in a chamber with 50

lice and their CO2 output determined. Recording the results

from these experiments presented several problems, because

a baseline of the lice CO2 output had to be determined prior

to introducing the air from the skin chamber. But the air

from the skin chamber had accumulated high concentrations

of CO and drove the instrument off scale. So a procedure

was devised by which the air from the skin chamber was first

flushed, then the air from the lice chamber (since it had

accumulated CO2 meantime) and finally the.two chambers were

connected together. At the end of an observation the skin

chamber was disconnected and the lice CO output allowed

to attain baseline conditions again. The CO2 output by the

skin of the arm was also measured by connecting the chamber

directly to the CO2 analizer (see Figures 9a and b).

Reactions to an artificial finger
and varied stimuli

The lice were observed walking on an arena floor of

arithmetic graph paper and their "tracks" recorded on a

similar paper. The arena was surrounded by white paper

walls and a lamp suspended overhead to diminish the problem

of differential illumination previously discussed. Indi-

vidual lice were stimulated using an artificial finger

(hereafter called "finger"). A 10 KJL, 2-watt resistor was

Figure 9a,

b. (a) Flow chart for monitoring the CO output
of lice during stimulation with human skin gaseous
emanations. The air could flow through five
different paths: A, directly to the analizer
for reference; B, through the arm chamber; C,
through thelice chamber; D, through both arm and
lice chambers; and E, flushed out of the system
after passing through the arm chamber. (b) Dia-
gramatic representation of the CO2 levels in the
system under the different pathways air flowed
through. Time is not scaled. See text for more


a 50
. o

T ime

covered with molding clay and this inserted into a finger of

a rubber glove; this finger had a final diameter of 1 cm.

The blackbody radiation output of the rubber glove is very

similar to human skin. The resistor functioned as a heater

and it was wired to a temperature controller which was

adjusted for a 33 C surface temperature. Lice were made to

follow the "finger" or the "finger" was brought close to

the path of walking lice to see how they would react to it.

In another arena designed to eliminate the convective

heat effect, the arena floor was made of fine ninon (fine

nylon fabric) stretched over a 10 cm diameter container, to

the bottom of which clean,dried air was supplied at the rate

of 12,000 cm min-1. Reactions of walking lice to the

"finger" were also studied in this arena.

Several unsuccessful attempts were made at sealing the

pegs on the tip of the antennae with different kinds of

glues, adhesives, paint, etc. Most of the time the material

did not stick or if it did, it peeled off when dry. Cutting

the antennae failed because the great amount of bleeding

was considered harmful; sealing the cut end also failed.

The pegs were finally removed by squeezing the extreme tip

of the antennae with a very sharp pair of tweezers while the

lice were anesthetized with CO2. Twenty-four hours after

this treatment the lice were allowed to feed on the

investigator's arm to compare their feeding behavior with

normal lice. They were also stimulated with the "finger."

Morphological studies of the antenna

Body lice antennae were studied using the light micro-.

scope and the transmission and scanning electron micro-

scopes. The studies concentrated on the pore and tuft

organs situated on the fourth and fifth segments, and the

pegs sensillae on the fifth.

Light microscopy

Antennae from ist, 2nd, and 3rd instar larvae and adult

lice were cut off and mounted on glass slides with a

clearing mounting media (CMC-10, General Biological Supply

House, Inc.) or resin (preservaslide, 60 percent resin in

xylene) for whole mount studies. The number of tactile

hairs, tufts and pegs present on the antennae of each instar

were recorded. Adult lice from the Burundi, Freetown and

Korean colonies were prepared in a similar manner. Pre-

served specimens of body and head lice (P.h. capitis)

loaned by the U. S. National Museum, Washington, D. C.,

through Dr. R. I. Sailer, USDA, ARS, ENT, IIPI Branch, and

specimens from the previously mentioned colonies were

studied regarding the number of pegs and tufts on the

antennae. This was done as a means of further documenting

the discrepancy in the number of tuft organs as stated by

Wigglesworth (1941) and by Miller (1969).

The crystal violet technique (Slifer, 1960).for iden-

tifying receptors with openings where nerve endings are

exposed to the air was used with fresh adult antennae. This

possibility of permeability of the walls of the basiconic

pegs was also investigated using aniline blue instead of

crystal violet (P. S. Callahan, personal communication,

1970). The pressure technique used by Slifer, Prestage and

Beams (1957) to locate open tip thick-walled sensors was

applied to fresh antennae. Other antennae were embedded

in paraffin and sectioned at 5 or 7 pm. These sections were

stained with Mallory's triple stain. Thick, 2 pm sections

of epoxy-embedded antennae for transmission electron micro-

scopy (see next section) were cut with the ultramicrotome

using glass knives and stained with Safranin O, Toluidine

Blue and Auromine 0 (R. M. Ropell and T. Carlysle, personal

communication, 1970). Examination of material was performed

using a Zeiss photomicroscope II, under phase contrast or

Nomarski differential interference contrast. Microscopic

measurements were made using an eyepiece micrometer.

Transmission electron microscopy

Antennae from live lice were fixed for 3 hours in

phosphate buffered 5 percent gluteraldehyde, washed in

buffer, osmicated for 4 hours in 1 percent OsO4 (osmium

tetraoxide), washed, carried through a dehydrating ethanol

series, then placed in propylene oxide and embedded in an

epon-araldite mixture (Mollenhauer, 1964). Ultrathin

sections were cut with a diamond knife on a Sorvall MT-2

ultramicrotome and picked up with Formvar-coated copper

grids. They were stained with saturated uranyl acetate and

lead citrate (Venable and Coggeshall, 1965). Examination of

sections was carried out on a Hitachi 125-E electron

microscope at accelerating voltages of 50 or 75 KV.

Scanning electron microscopy

Lice heads were fixed in 5 percent glutaraldehyde.

Some specimens were post-fixed in 1 percent OsO4. Some of

these post-fixed heads were sonicated in a Sonicator (Ladd

Research Industries, Inc.) to cause breakage of some of

the pegs, since it had been observed that osmic fixation

caused them to become very brittle. The heads were mounted

on specimen stubs with a silver base paint; some of them

were coated with 200-300 A gold or gold-palladium in a

Denton DV-502 high vacuum evaporator, others were examined

with no coating. Examination was done with a Cambridge

Mark II A Stereoscan Microscope at operating voltages of

5-20 KV.



Straight arena experiments

The results from the straight arena clearly indicated

that lice responded selectively to the blackbody. Mean

values of percent-responding lice per compartment are

summarized in Table 1. The percent and their weighted

values for the blackbody and aluminum sides of the arena

are shown in Table 2, together with the "t" statistic for

comparison between the two sides. The records of lice on

the blackbody side were significantly higher (0.01 level)

than on the aluminum, at both times tested, 5 and 3 minutes.

No difference was obtained in the control experiments, that

is, while the heaters were off. Weighting the raw data,

according to the relative position of the compartment,

lowered the values, but did not affect the significance of

the results.

The number of lice "responding" when the heaters were

on was greater (highly significant) than during control

experiments (Table 3). The 2-minute difference between


Table 1

Percent of the total number of responding lice
recorded at each compartment in the straight arena.
Eight replications per experiment.

Heaters on Control

Compartthent x Sx x Sx
5 Min.
+3 31.5 8.54 15.2 10.26
+2 16.2 4.64 11.4 13.53
+1 12.8 8.12 24.0 20.45

-3 16.3 7.49 13.0 7.51
-2 13.5 7.23 18.2 5.84
-1 9.7 5.94 19.2 7.93

3 Min.
+3 39.2 13.42 23.1 16.33
+2 17.2 6.26 9.1 11.43
+1 8.8 4.49 16.5 14.42

-3 19.8 12.27 19.5 15.36
-2 8.8 6.59 23.7 7.31
-1 7.2 4.35 9.1 9.09


0 0

S0 0
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H 3 -14 1

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r. 0 04
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Table 3

Average number of lice (out of 50) responding when
the heaters were on or off (control) in the straight arena.
Results are of 8 replications each.




5 Min 36.8 17.5 5.47**

3 Min 32.2 13.2 3.24**

"t" .91 1.27
N.S. N.S.

**Highly significant at a 0.01 level.

N.S. Not significant at a 0.10 level.

the 3-and 5-minute experiments did not make any difference

between the recorded number of responding lice. Perhaps,

if shorter times had been used, a difference would have

appeared. Wigglesworth (1941) reported that lice moved at

an average speed of 27.2 cm min-1 at 21 C and the speed in-

creased to 37.5 cm min at 29C. Since my experiments were

conducted at 22 C a speed of about 28 cm min- can be as-

sumed. A louse released in the center of the arena facing

toward the aluminum side would keep moving in that general

direction (discussed in the Review of Literature). At the

end of the arena or compartment -3 it would continue along

the walls because of its strong thigmotaxis and thus move

toward the blackbody side. Upon perceiving the stimulus on

this side it would remain there. The total distance of 36

cm in a straight course could be easily covered in the 3

minutes. This would explain the greater number of lice

recorded at +3 than at any other compartment. This experi-

ment did not demonstrate that lice can detect IR from 12 cm

away, as it may appear. As discussed in the Review of

Literature, it has been reported that some blood-sucking

insects can detect the hosts "warmth" from only 4-5 cm away

(see next section).

Even though the heaters were above the arena the con-

vective heat arising from them may still have affected the

lice. These experiments did not eliminate the convective

heat as a factor, as will be seen in the next section.

Round arena experiments

The round arena experiments studied the alleged role of

convective heat on the detection of thehost's warmth by

blood-sucking insects. The curtain of moving air (about 220

cm min- ) eliminated the convective heat arising from the

walls of the tape heater and its effect on the lice. The

percentages of the lice recorded beyond the 5.5 cm radius

circle (3.25 cm from the heater surface) in front of the

blackbody strips were higher than the percentages in front

of the aluminum strips. A "t" test demonstrated that the

difference was significant at confidence levels higher than

99 percent (Table 4). Control experiments, that is, with

the heater off, did not show any difference between the BB

and Al areas, even at the confidence levels of 0.50. By

eliminating the convective heat, these results clearly

demonstrated that lice were not reacting to the convective

heat, as proposed by Wigglesworth (1941), but to the total

IR output of the walls of the heater. The number of lice

considered to have responded when the heater was on was

significantly greater (0.01 level) compared to the number

when it was off. This is explained by the observation that

lice become more active when close to an IR source.


0. 0 00

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Results from the experiments with the arena cut into

strips of different lengths and facing each heater area

demonstrated thatlice could detect the difference in IR

output between BB and Al at distances of 3.25 cm, but not at

4.75 or 7.5 cm. The 1.5, 3.0 and 55 cm strips were detached

from the solid center of the arena at distances of 3.25,

4.75 and 7.5 cm from the heater surface, respectively.

Therefore, these were the distances from the IR source at

which a louse left the arena center area and entered one of

the 1 cm-wide strips and was recorded as "responding." The

louse was committed to a particular strip at this distance

from the heater. Since approximately equal numbers were

recorded on strips facing Al and BB, it can be assumed that

when the IR stimulus was absent the lice moved at random

(see Table 4). In the case of the 6.0 cm arena (1.5 cm

strip) the lice may have outwardly dispersed at random.

Those lice that walked right into one of the strips may

have kept moving straight until reaching the corduroy

"trap." But a louse reaching the arena edge, in between

strips, moved along this edge (because of its strong

thigmotaxis) until it encountered a strip and followed the

edge of the strip. It is this group of lice reaching the

arena edge that makes the choice of strip, i.e., either

moving toward the IR source and therefore following the

arena edge until reaching a strip, or moving toward the Al

side and being "trapped" at the end of that strip.

The number of lice that "responded" with the heater on

was greater in the 1.5 cm strip experiment (0.10 level) as

seen on Table 5. No difference was observed between the

number responding in the 3.0 cm and 5.5 cm strips experi-

ments. This further substantiates the fact that lice

detected IR at 3.25 cm away but not a 4.75 or 7.5 cm.

CO2 monitoring experiments

These experiments were designed to quantify the ob-

served response of lice to blackbody IR radiation stimula-

tion as an increase in their locomotive activity. Quanti-

fication was possible by equating locomotive activity to

CO2 output of 50, one-day-starved adult lice. The major

problem encountered during these experiments was that CO2

production by the same number of lice, with no stimulus

offered, varied considerably, and thus prevented-pooling the

data of repeated experiments. The data were pooled in cases

in which the CO2 concentration baselines were the same for

two different sets of 50 lice from the same rearing batch.

When two groups of 50 lice were maintained for 6 hours

with no stimulus under similar conditions and their CO2

output recorded every 5 minutes, they had CO2 baselines of

Table 5

Percent of lice recorded as responding to IR stimulation
in the round arena. Results of 5 tests per arena type,
4 replications per arena.

Heater on

x Sx









Heater off

x Sx












0.93 N.S.

0.82 N.S.

* Significant at a 0.05 level.
**Highly significant at a 0.01 level.
N.S. Not significant at a 0.10 level.



1.5 cm

3.0 cm

5.5 cm

" I

21.0 and 23.5 ppm. The standard deviations were 1.15 and

1.08 ppm, respectively. There was very little variation in

CO2 output over a long period of time, when conditions

were constant. Baselines obtained in subsequent experiments

ranged from 20.0 to 42.0 ppm. Several types of control

experiments (see Figures 8b and c) demonstrated that the

increase in CO2 was not an artifact of the experimental

arrangement. When no lice were in the chamber with the

heaters and these heaters were on, no increase of the CO2

above the zero line was observed; not even in cases in which

both heaters, BB and Al, were turned on at the same time,

demonstrating that the CO2 differential was produced by the

lice. In other experiments the lice were held in a chamber

preceding the one with the heaters, and the heaters were

turned on (see Figure 8c). No increase in the CO2 concen-

tration above the baseline was observed demonstrating that

any increase in the CO2 reading was not due to heating of

CO2 by the heaters or that the CO2 analizer was reacting

to the small increase in the air temperature inside the

heater chamber. I do not know if this temperature change

remained after the air had passed through the narrow air

hose and reached the CO2 analizer. In another control

experiment, which consisted of reversing the chamber order,

that is, the heaters preceding the lice chamber (see

Figure 8b), no change in CO2 above baseline resulted. This

proved that the lice were not reacting to any effect the

heaters may have had on the system's air. The ideal con-

trol would have been to heat the air before it entered the'

lice chamber, but several attempts to do this using differ-

ent types of heaterswere unsuccessful, since the air was in

a closed system and moving at a fast flow rate of 7.007 m

min-1; no significant heating was obtained. However, it is

shown later that the air temperature within the lice chamber

did not influence the lice output of CO2' i.e., the lice

kinetic activity.

Results from the experimental condition when two sets

of 50 lice were subjected to heating of both the BB and Al

heaters are summarized in Table 6 (see Figures 10a and 10b).

These values represent averages of readings taken every 2.5

minutes while either the BB or the Al heaters were on for

65 min (60 min were allowed between heating). The data were

pooled because the lice sets had equal CO2 baselines, 22.0


The difference between the CO2 output when the BB was

constantly on and when the Al was on was highly significant

(0.01 level). The temperature inside the chamber was

raised by the same amount when either the Al and BB were on.

Therefore, the lice reaction was not due to a temperature

Table 6

Chamber temperature and CO2 concentration when
BB or Al heaters were maintained at 33 C for
65 min. Fifty lice in the chamber.

Temperature (C) (a)

x Sx

28.23 0.197


0.409 N.S.

28.21 0.224



CO? (ppm)

Sx ",t"



25.24 2.24

(a)Temperature during off period was
**Highly significant difference at a
N.S. Not significant difference at a

27.22 C.
0.01 level.
0.10 level.





Figures lOa, b, c. CO2 output of lice during constant
stimulation under (a) aluminum and (b) blackbody
radiators, or (c) when both heaters were alter-
nately turned on and off with a 2.5 min off
period inbetween. Response delay represents the
inherent lag on the system response due to air
flow from the lice chamber to the CO2 analizer;
it was approximately 1.1 min.









uwdd Zoo

change, but to the differential output of IR from the BB.

The next experiments tested the effect of BB or Al

heating in short intervals on lice activity. For this,

the heaters were turned on and off for periods of 2.5 min,

one heater at a time (see Figures lla and b) and letting one

hour elapse before testing the other heater. Lice from the

same rearing batch were used and their data pooled because

of their similar CO2 baseline, 41.5 ppm (Table 7). Neither

the temperature at time-off (T-off) nor the change in

temperature (At) varied between the Al and BB stimulation,

but the CO2 concentration at time-off (C02-off) and the

change in CO2 concentration (ACO2) was highly significant

(Table 7). The CO2 concentration during Al heating did not

increase above the CO2 baseline limits.

One fact, not shown in Table 7, is that the initial

increase in CO2 concentration when the BB was turned on for

the first time was the greatest CO2 change (ACO ) and sub-

sequent changes due to BB IR stimulation were smaller; less

than one-half of the initial rise (see Figure llb). The

reason for the decrease in ACO2 after the initial BB stimu-

lation was that BB was turned on each time before the CO2

concentration had declined to a base level. A longer off-

interval would have eliminated this artifact, but this would

also have defeated the purpose of repeated BB IR stimulation

Figures lla, b. CO2 output of lice during periodic stimula-
tion under (a) aluminum and (b) blackbody radiators.
Time periods were 2.5 min. Response delay repre-
sents the inherent lag on the system response due
to air flow from the lice chamber to the CO2
analizer, it was approximately 1.1 min.




u dd g0o

*H J

.ri c%14 ) 0
S* U X1


U) o

0 ) 044 < 0 0
> 0 C4N E
0 ) 0 X o
( e, I 0
o -,

O4 0
-O ,-
104 M (

H 3 0 V 0p 4-1 .
,Q *H A = .
i --i 0

H-1 *r &4 4* 0
-I Q )0 4J
0 D 0
I 0 r 0
S0 > 0 *
o () o *lr o o

4-) .>r He H
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44 0 a) I to E) u

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t4.- 5
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within short periods of time. Even so, the ACO2 values

were large enough to show the high degree of difference in

the lice activity between BB and Al heating.

Four experiments were conducted, each with at least 10

replications, in which the BB and Al heaters were alter-

nately turned on and off, with an off period in between

them (see Figure 1Oc). All time periods were 2.5 minutes.

Data from these experiments could not be pooled because of

the great difference among their CO2 baselines (33.0, 42.0,

32.5, 21.8 ppm). So, each experiment was analyzed sepa-

rately using the recorded values of the temperature in the

lice chamber when the heaters were turned on (T-on) and

off (T-off). The change in chamber temperature was de-

termined as the difference between T-off and T-on. CO2

concentrations were recorded from the strip chart when the

heaters were turned on (C02-on) and off (C02-off). The

change in CO2 concentration (ACO2) was computed as a

difference in concentration between heater off and on.

The value for T-off during BB-on and Al-on were

significantly different (Table 8). The At values were also

the same for the BB-on and Al-on periods. However, the

C02-off concentrations were greater during the BB-on periods.

In three of the tests, C02-off values were highly signifi-

cant (at a 0.01 level) and significant in the fourth test

0* r 4 *

00 1N H C 0
CO ^ r-I *
* *Omt )N *
000r-O A (r

o 4l

* 0

r-I I

CN r-l r- Li
* '1C *
10H'IC .0c'




U *

a)44 0

g0 C
Un a


a( )

4 a)



0 (0 0

4J -

0 4


4C 0

4 -

00 0
0 r--I

0 r0



. 0 0
.*** ~h

* *

0 () CO
* 9
o o.

* h

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1x Ix


IX IX = 44


m C-
H *

4* *

c4 O; 4c

e o


= CO) CO


4 U


H r-
n4 N



0 r-l *
OO *


* fn *

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0 00





-A -
CO r-1

c *
*rl 0




r r-4
a0) a
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0> 0

Q) *


4(a 00
4 0 4(U

ri- -.1


.I 44

4> 4 1

O *rl

** *
c4a o

(0.05). Subsequently, the CO2 values were also greater

during BB-on periods; but the ACO2 values for the Al-on

periods resulted in negative values in the majority of

cases. These negative values were obtained because the

lice did not react during the Al-on periods (see Figure

10c). This same effect was discussed in the previous


It can be stated that the environmental temperature

did not have any effect on the kinetic state of the lice,

which was related to CO2 output, but it was the differen-

tial output of IR by the BB that made the difference.

The effect of human skin emanations upon lice behavior

is summarized in Table 9. The values are the results of 10

readings with each of the two human volunteers, M. S. and

K. F. The skin area,circumscribed by the chamber through
which air was passed, was 9.61 cm Average output by these

skin areas of the two volunteers were 9.2 and 8.4 ppm

(average for the two, 8.8 ppm) when an air flow of 50 cc

min was maintained, representing 5 X 105 cc of CO per

minute. The human skin produces many volatile chemicals

(U. S. Department of the Army, 1966); among them is lactic

acid, which has been demonstrated to be an attractant for

mosquitoes (Acree et al., 1968). When the lice were stimu-

lated with human skin emanations under the experimental

Table 9

Effect of human skin air emanations on CO output of
50 one-day-starved body lice (refer to Figures 14
and 15 for descriptions).

CO2 (ppm)

Volunteer MS Volunteer KS
Constants x Sx x Sx

Arm (B) 9.2 0.45 8.4 0.89
Lice (C) 18.5 0.88 33.4 0.99
Arm + Lice (D) 29.5 1.37 41.5 1.20


Lice (during E) (b) 19.0 1.30 33.4 0.55
Arm + Lice (D-off) (c) 28.4 1.14 41.0 1.58
D-off-Lice (during E) (d) 9.2 .84 7.6 1.67

(a) Constants are valuesobtained by connecting directly the
arm (B) or lice (C) to CO2 analizer. Arm + lice refers
to the CO2 concentration at D position during an

(b) Values of CO2 from lice during arm flushing prior to
any experiment.

(c) CO2 values at end of time D (D-off) when the arm line
was disconnected from the lice line.

(d) Values of subtracting lice values from D-off (and
obtaining similar value to arm B).

conditions, they did not become active, i.e., their CO2

output did not increase above levels at an akinetic state

(Table 9). This was shown by subtracting the skin and the

lice CO2 baselines from the CO2 readings when the two, arm

and lice, were connected to the line.

Reactions to an artificial finger
and varied stimuli

Lice reactions to stimulation by an artificial finger

at 33 C were difficult to quantify. The majority of experi-

ments were recorded as observations of behavior patterns

and each type of observation was recorded from no less than

20 lice. Behavioral observations were recorded from normal

lice and in some cases from lice whose last antennal segment ,

had been removed, and are referred to as antennectomized

lice. It appears best to summarize and comment on these


a. If a warm "finger" was slowly lowered to within

1.0 cm from an arena floor where lice were in an akinetic

state, they began "awakening" over circle with a radius

of about 3 cm. If a cool "finger" was used instead, the

lice remained in the akinetic state.

b. Normal lice followed a warm "finger" if it was

maintained a short distance ahead in front of them. They

did not follow or respond to a cool "finger." Similarly,

antennectomized lice followed a warm "finger" but not a

cool one. If the lice began following a warm "finger" which

was quickly replaced by a cool one, the lice continued

following it momentarily. The cool "finger," however, would

rapidly lose its attraction for the lice and they would move

in another direction. If the procedure was repeated with

antennectionized lice they kept following the cool "finger"

for a longer period of time before losing interest and

moving in another direction.

c. Normal lice followed a warm "finger" even in a

situation when the arena was made of fine ninon and clean

air was blown from underneath at a rate of 344 ml cm2

d. If normal lice were stimulated with a warm "finger"

held 1.0 cm above the arena floor, the lice raised their

heads and front legs, displaying an upward questing

response (trying to grab). If this was repeated with an-

tennectomized lice, they remained under the "finger," but

they did not show the upward questing response.

e. If normal lice were crawling on a more or less

straight course and encountered a spot that had been warmed

by close contact with the warm "finger," they veered to

either side but then returned again to the more-or-less

straight line. This same behavior was shown by antennec-

tomized lice. This would be indicative of a klino-kinetic


f. When a warm "finger" was positioned on the vertical

0.5 cm from the arena floor and to the side of the general

direction that normal lice were following, the lice either

turned toward the "finger" or maintained the original

straight direction. This depended on the angle subtended

by the initial starting point of the straight line direc-

tion of the lice and the "finger." This means the angle

measured was based on the following three points: (1) any

point ahead on the line of movement, (2) the initial point

of the lice movement, and (3) the position of the "finger"

in relation to the line of lice movement. Of 30 measure-

ments, 13 angles were greater than 370 and the lice main-

tained a straight course. The remaining 17 angles were

smaller than 310 and the lice turned toward the "finger"

and reached it. This experiment was repeated with antennec-

tomized lice and the turning occurred only when the "finger"

was positioned on the general direction of the lice move-


g. If the "finger" was brought close from underneath

to normal lice crawling on an arena floor made of.ninon,

the lice moved in circles around the "finger" position.

When the "finger" was removed the lice reached and crawled

along close to the arena wall. The same behavior was ob-

served with antennectomized lice. This suggests that

perception of "warmth" can take place from underneath the


h. When one-day-starved, normal lice were released on

the skin of a volunteer's arm, they began feeding within an

average time of 5.8 seconds (standard deviation, 2.3 sec).

Initiation of biting was considered to be the time at which

the lice arched their abdomen upward pushing against the

substrate with the caudal tip of their abdomen. One-day-

starved antennectomized lice (amputation performed the

previous day) began feeding within an average time of 15.0

sec (standard deviation, 8.4 sec). A "t" test showed these

time differences to be highly significant (0.01 level).

i. Neither normal or antennectomized lice fed on an

arm skin made cold with ice.

j. When a heater tape (at 33 C) was covered with the

upper portion of a rubber glove, which is very smooth, lice

did not attempt any feeding. But if the heater was covered

with the inner palm area of the glove, which is very rough,

the lice initiated feeding behavior. Both normal and

antennectomized lice showed this behavior.

The significance of.blackbody IR detection

An established fact is that when a hand ie brought

close to akinetic lice they'become, within seconds, very

active. Behavioral experiments, reported in this study,

demonstrated that lice became very active when stimulated by

blackbody IR radiation. Experiments also demonstrated that

lice attempted feeding on warm, clean rubber, but did not

show any feeding behavior when the human skin was cooled

with ice. All these facts raise doubts over the value of

olfaction in host detection and in feeding stimulation. The

facts also point to the importance of blackbody IR as a

token stimulus in hostdetection by body lice.

Howlett (1917) pointed out the advantage of lice get-

ting excited when stimulated by "warmth," the main advantage

being "in securing the wider distribution of the species by

infecting anyone whose body came in contact with that of

their host." Of course, the advantage is not cc -un species,

but to the louse which wanders away from its host.

Air currents carrying lice eggs on failing hair or

cloth threads is a common mode of d.spersi-m.. The newly

hatched larvae have to find their host. Hence, the reaction

to blackbody IR is advantageous, because by actively moving

only when the host is in close proximity, it increases the

chances of rewarding the energy expenditure with a blood

meal and economizing energies in the absence of a host. If

the size and means of locomotion of lice are considered from