Robert B. Willey and Ruth L. Willey.
Visual and Acoustical Social Displays by the Grasshopper Arphia conspersa (Orthoptera: Acrididae).
Psyche 76:280-305, 1969.

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VISUAL AND ACOUSTICAL SOCIAL DISPLAYS
BY THE GRASSHOPPER ARPHIA CONSPERSA
(ORTHOPTERA : ACRIDIDAE) '9 '
BY ROBERT B. WILLEY AND RUTH L. WILLEY~
Many species of the Oedipodinae (band-wing grasshoppers) exhibit strikingly diverse social interactions invoking visual and acoustical communication between the sexes and between individuals of the same sex (Otte, 1968, 1969).
The present paper is an account of the communication system of Arphia conspersa and will serve as an introduction to quantitative and experimental analyses of specific aspects of the behavior of this and other species.
LIFE HISTORY
Arphia conspersa is widespread throughout the western Great Plains from northern Mexico to the souithern provinces of Canada and is found up to 11,000 feet elevation in the Rocky Mountains of southern Colorado where this study was made. We have found that these populations 'typically overwinter as nymphs and the eggs usually need a cold period to break diapause, implying a two-year life cycle. In the mountain areas near Gunnison, Colorado, adults have emerged consistently (1962-1968) four to five weeks after the snow has melted
(June to July). The peak of abundance occurs abouit two weeks after the first observed emergence and the popu- lation dies out about three weeks later in most localities (Willey and Willey, 1967). In the vicinity of Boulder, however, a few adults may be found at all months of the year, even in open areas during warm days of the winter (Halliburton & Alexander, 1964). At higher elevations such as at Gothic (9,500 feet, Gunnison Co.) and Black Mesa (9,700 feet, Montrose-Gunnison Cos.) adults pass through most of their life without coming into contact with adults 'Research conducted at the Rocky Mountain Biological Laboratory, Crested Butte, Colorado; The University of Illinois at Chicago Circle; National Center for Atmospheric Research, Boulder, Colorado; and Ripon College, Wisconsin.
'This study was supported in part by grant GB-2201 from the National Science Foundation, three grants from the Graduate Research Board of the University of Illinois, and Sigma Xi-RESA Grants-in-Aid of Research for the summers of 1963 and 1968.
'Address of the co-authors: Department of Biological Sciences, Univer- sity of Illinois at Chicago Circle, Box 4348, Chicago, Illinois 60680.



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19691 Willey and Willey - Social Displays 28 I of other related species, except for sparse populations of Aeropedellus chatus (Acridinae). At lower elevations. Xanihippus coralh@s, another oedipodine, is commonly sympatric with A. consperm The densest populations so far observed occur in short grass prairie parks near Los Pinos Pass (10,200 feet, Saquache Co.), Black Mesa, and Table Mesa (6,200 feet, Boulder Co.). We have counted as
many as 60 males per acre, but usually the population averages fewer than 20 per acre with more or less clumped distribution. These densities would seem to be relatively low for efficiency of loca- tion of mates and may be correlated with the highly evolved signals for social communication described below. Figure 1. Male A. corrq5rrsa in alert pose, Table Mesa, Boulder Co. This male also was buzzing with the right hind leg (visible as 2 faint diagonal streaks).
MATERIALS AND METHODS
Field observations entailed sitting or standing quietly in the center of a population cluster. The members of this species are unwary enough to behave normally within a few inches of the observer. Completion of behavioral sequences have been observed on our nets, clothing and boots. Notetaking and scoring an outline sheet did not disturb the grasshoppers. Climatic conditions were noted; in a few



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282 Psyche [September
experiments temperature and wind speed were measured with record- ing equipment. This study is still in progress. Most observations were made of Gothic, Black Mesa, Table Mesa and Los Pinos Pass populations from 1961 to the present Observations were also made on wild-caught and reared grass- hoppers kept in a variety of cages.
The most successful cage con-
sisted of a simple plastic plant tray 8" X 12" filled with sand with wire screening over the 'top to form a "quonset". Two removable
solid wooden semi-circles formed the ends. Young shoots of blue
grass, rye grass, and dandelions were provided for food during the seasons when wild grasses were unavailable. A 60 or IOOW bulb provided heat and light which attracted the grasshoppers into a closely interacting group.
Movements were recorded wilth a Camex 8 mm. reflex camera run at 16 and 32 frames per second, while sounds were recorded with a Nagra I11 tape system and an AKG condenser microphone (C6o with B6o power supply) equipped with a 24 inch parabolic reflector (Torngren Co.) for field recording from distances over 2 feet. Recordings were made in the laboratory without the parabola and, recently, with a Sennheiser 804 condenser microphone. Fre- quency response was checked with the 4000 Hz calibration tone of the Nagra. The movie film was Kodachrome I1 and the audio- tape was Scotch 138. The audiospectrograms were produced on a Kay Electric Co. Model 675 Missile Data-Reduction Spectrograph (Missilyzer). The overall sound range of each audiospectrogram illustrated in this report was calibrated at the time of transfer to the spectrographic paper with a calibrated precision sine-square wave generator (model E-310). We also cross-checked the recorded calibration tones of the Nagi-a and the generator. We measured the overall
amplitude of the sounds directly from the insect with a model 1551C sound level meter (General Radio Co.). The be- havioral vocabulary is derived from Willey & Willey ( I 964), R. Alexander ( I 967)) and Otte ( 1968).
OBSERVATIONS
Solitary behavior
Males tend to be more active than females. They wander over
the ground for distances up to 6 feet in a random path more or less determined by the microtopography. The manner of walking in males is a spurt of several complete leg movement sequences sepa-



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19691 Willey and Willey - Social Displays 283 rated from the next sequence by a fractional-second pause. This spurt-walk becomes accentuated by a rapid raising and lowering of both hind legs with an open femoro-tibia1 angle of about 30'. One or two such flicks may occur whenever both hind legs are not in contact with the ground. The male, when approaching a high point, such as a pebble or a stick, often crawls'i upon it and stands in a motionless "alert pose" as in Figure I. At this time the male is very responsive to any sudden movement or sound on the part of the observer. Usually the visible reaction to a disturbance is a slight crouch, lifting of the antennae to the vertical, closing of the femoro- tibia1 angle of 'the hind legs and lowering of the hind femora to the horizontal. The subsequent reaction is usually a leap and flight. If the male is allowed to recover from the initial disturbance, he slowly resumes the alert pose and periodically snaps the hind femora to the vertical in a flicking motion up and down, singly or together. Minor disturbances such as small insects coming too close or a grass blade touching him will cause such a flick. In fact, some flicks seem to be spontaneous during the alert pose. Social behavior
Signals associated with social interaction are ( I ) spontaneous flightts which are accompanied by a clicking sound (crepitation) pro- duced by the wings,
(2) simple soundless flicks of the hind legs ( "femur-tipping", Otte, I 968) , (3 ) femoro-tegminal stridulations which generate chirps, rasps, buzzes and squeals; and (4) soundless movements observed during contact between two grasshoppers which include tapping with the prothoracic tarsus, palpating with the antennae, rapid stroking with the palpi, butting with the frons, mounting by the male and, of course, genital contact. The emphasis in this paper will be placed on those signals transmitted at a distance between two or more individuals.
A signal, by our definition, must have some reaction-potential in the organism perceiving it. Our operational definition for a visual or auditory communication signal is the production of a measurable motion and/or airborne acoustical vibration by one individual fol- lowed in another individual by an action unrelated to what the latter was doing and unlikely to have occurred in the absence of the stimulation. Chemical signals could not be recorded in the present study. Frequent sounds such as mandible clicks, wing buzzes, sub- strate tapping with the tarsi, and tibio-tegminal clicks have produced no observable response in this species, and will not be considered in detail.




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284 Psyche [September




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Willey and Willey - Social Displays
The flight crepitation.
The spontaneous aerial crepitation is a buzzing flight, which lasts one to three seconds, during which the grasshopper describes an arc one to ten feet in length and three feet in height. Males make more crepitation flights, by far, than females, which seldom are seen in flight except during the first weeks of the season. The flights by males may be repeated in a minute, but they average only one such sequence every three to four minutes at 'the peak of daily activity during the most active part of the short adult season. Even if disturbed, these insects usually crepitate normally. Only when dis- turbed a second time will they fly away relatively soundlessly. Crepitation flights are usually into the wind if there is only a slight breeze, although such flights are suppressed entirely by wind above 10 m.p.h. On the other hand, silent escape flights are usually at least 30 feet in length and often extend over several hundred feet, flying with the wind (Willey & Willey, 1967).
The sound produced by the wings during crepitation is shown in Figure 2. Each pulse is a broad spectrum click with no distinct fundamental frequency nor apparent harmonic. The highest ampli- tudes are in a range from 3000 to 8000 Hz and the total range of the sound is restricted by the effective frequency response of the recording system (20 to 18,ooo Hz). To the human ear it is tone- less and sharp. There are about 45 pulses per second and they are evenly spaced unless a change of direction or landing occurs. At these times the pulses take on an added component, appearing double, and are more closely spaced. These changes are probably due to the wings beating faster and out of phase with one another. Mate-female interaction (courtship and copulation). The chirp is the primary sound generated by the male during courtship. This sound is produced by rubbing a ridge on the medial side of the hind femur on a linear series of pegs situated in both sexes on a modified intercalary vein of the tegmen. The chirp is a unitary sound probably produced by an intense pressure of the femur on the tegmen in a smooth up and down stroke cycle. As can be Figure 2. Field recording of beginning and ending of flight crepitation. This flight began 3 feet from the microphone, described a long arc to 10 feet away and returned to the same spot. Note the increased pulse rate ( wing beat frequncy) as the insect gains altitude. The pulse rate in mid-flight is more regular. Also note the double wave fronts as the insect lands, probably representing wings beating out of phase with one another. The break in the middle of the display = 1.8 seconds. Figure 3. Audiospectrogram of Exakta camera re-set sounds.



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286 Psyche [September




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19691 Willey and Willey - Social Displays 287 seen in Fig, 4, each chirp ranges to the limits of the recording apparatus but has an intense band about 500 cycles wide slurring upward and downward many times between IW arid 5000 Hz with a duration of 40-80 msec. Each slur is probably a small multi- ple acoustic effect of a short series of pegs on a resonating wing and the slurring effect probably is a function of pressure, velocity, and changing strike angle of the femoral ridge as it arcs along the pegs. Additional faint overtones are observed at 7000 to 9000 Hz and 12000 to 16000 Hz.
They are not likely to be heard by human ears and probably are an artifact of the spectrograph (Watkins, 1967). A sound between 3000 and 5000 Hz is usually picked up as approximating the tonal quality of the chirp. Chirps differ inter se in many ways and can be weak, strong, produced on the upstroke, downstroke, or both, high pitched, low pitched, etc. The average duration of a chirp is 60 msec and, when combined with other chirps in a phrase, has no standard interval. The sound intensity is difficult to measure directly, since the chirp is usually unitary and the Figure 4.
Laboratory recording of chirps; the multiple chirps were at the beginning of a courtship sequence in which the male attempted to mount immediately, was repulsed at first, followed the female for nearly a minute giving unitary chirps and finally mounted and successfully copulated. The similarity of the peaks in the major (== fundamental) frequency band indicated that this is a single movement by both legs, either up stroke or down stroke.
The "ghost" harmonics every 3-5 KHz
probably indicates a basic spike pulse modulated by the number of pulses ( teeth on the intercalary vein) struck per sedgiven instant (Watkins, 1967), but this must be checked further. The unitary chirp and multiple chirps were selected separately and are not in any determined time relation to each other.
Figure 5. Audiospectrogram of chipmunk (Eutamias sp.) alarm cry. The fundamental frequency of this complex sound seems to be 1 to 8 KHz which to human ears would average a high grasshopper chirp of 5 KHz. Since grasshoppers probably are tone deaf, the amplitude (at greater distance), great directionality of the sound, its duration, and spacing could be a good mimic of the chirp, thus causing the orientation of the two males described in the text.
Figure 6. Audiospectrogram of crepitation and squeal of two individuals in a caged population outdoors. The crepitation is separated from the squeal by two broad dark lines representing the landing of the insect on the wire netting. A smaller dark spot at about 1500 Hz represents a third impact on the wire. The squeal is difficult to reproduce clearly and is of much less amplitude than the crepitation and nearly the same as the back- ground air noises. However, the great variation in carrier frequency shows the basic pattern. The 5 ascending major frequency peaks may represent multiple strokes, but at present we cannot ascertain how many strokes are produced nor what mechanism modulates the pulse rate frequency.



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288 Psyche [September
needle of a sound level meter is not deflected fully by it. However, a strong chirp seems to peak at 50 db at 4" on the A and B scales. [All readings use a reference level of o db Ì 0.0002 microbar, alt. 9500 ft., and the scales used are those recommended by P'eter- son and Gross (1963) for the given sound level and frequency.] Males can usually detect a female as a female from at least two feet and spurt-run toward her emitting separated high intensity chirps as above. Figure 7 illustrates the general schema of courtship of receptive and non-receptive females. The female "signal" seems to be an inadvertent movement such as feeding, walking, grooming or no movement at all. Her greater size probably also is a sign stimulus. The male chirps vary from pulsed phrases of one to five chirps in succession. When he has approached within one inch of the female, he typically orients by facing her directly, frons to frons. The two grasshoppers "fence" mutually with their antennae and the male continues chirping. The male then moves to the female's side and faces her thorax. He may chirp and he may even butt his frons against the side of the thorax. The male finally places a prothoracic tarsus on her metathoracic femur, pats the substrate with his hind tarsi several times very rapidly and then attempts to mount from the rear of the female. Simultaneously, there often is a train of 4-5 chirps just before mounting. Females seem to be sexually responsive as virgins 10 days after molt and again after laying the first egg pod. However, these data are derived from females that were group-isolated as nymphs until presentation of the males and it has been shown by Highnam & Lusis ( 1962) that isolated females of Schistocerca gregaria mature more slowly. We considered a female receptive if copulation was completed. Some females actively solicited attention by males. After the short bout of antenna1 fencing initiated by mutual orientation and approach by both male and female, the female often turned while the male chirped, presented her side to the male, lowered the near hind leg and raised her opposite leg and both tegmina, exposing the wholle abdomen. The valves of the ovipositor may open or at least move a bit. At this point three females of the total of 20 successful court- ships observed fluttered the hind f emoro-tibia1 joint against the ground but not high enough to contact the tegmen. After this the male gave his final burst of chirps and mounted. In one case, in which an old male of four weeks was involved, the female initially followed the male and patted his wing tip with a fore tarsus, while he ran away from her giving the male flutter-rasp (q.v.). Then he



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MATING BEHAVIOR IN ARPHIA CONSPERSA
BEHAVIOR dd RELEASER
BEHAVIOR 00 NOWRECEPTIVE
BEHAVIOR 00 RECEPTIVE
RELEASER
SEARCH CF. ALER1 POS5
ORIENTATION
ANY MOT'ON
ANY MOTION. SPONT CF,
PRODUCEPHEROMONE
AFTER OklPOSITION (?I
I
ORIENTEO APPROACH
VISUAL. AUDITORY
ORIENTEO APPROACH VISUAL AUDITORY
*-;
CROUCH ESCAPE OR MOTiONLESS
CHIRP. CF. (ANY SIGNAL? /
ANTENNA-FENCE,
STROKE 0 HIND FEMUR/PLEUROH
VISUAL, TACTILE
WITH TARSI + ANTENNAE
ANTENNAL t FORETARSAL
STROKING OF 0' IO'OISORIENTEOI.
ANTENNA- FENCE
VISUAL TACTILE
CHEMICAL 171
STROKE 0 HIND FEMUR/PLEUROH
-
VISLIAL, TACTILE
-
WAVE HIND TIDIAE
REMAIN MOTIONLESS OR ESCAPE
VISUAL, TACTILE
*
CHEMOCONTACT 191
TACTILE, VISUAL
CHEMOCONTACT f?) *
BURST OF CHIRPS WHILE 1 TO Q'S PLEURON
PRESENT SIDE TO O! MOTIONLESS,
SUNNING POSE. ABO EXPOSED
ANTENNA-LASH
1
BACK AWAY.
REORIENT ELSE WHERE, +
BUZZ, FEED, GROOM
WAVING FREO CreS deC
I FEMORA 1 1 0 ABD
TIBIAE EXTENDED OR PARTLY FLEXED
MOUNT. PALP-MbND CONTACT WITH
MOTIONLESS. OR VIBRATE HIND
E M - TIE JOINT ON GROUND
o PRONOTUM , ANTENNA-LASH
I
COPULATORY TWISTS
KICK VIOLENTLY,
OR MOTIONLESS
GENITALIA CLOSED
MOTIONLESS, RAISE TIP OF ABD.
WITH SPERMATOPHORE PI
BUZZ FEED, GROOM
PERMIT COPULATION.
SUPPRESS RESPONSE
TO EXTERNAL STIMULI
COPULATION 20-60 MIN
SUPPRESS RESPONSE TO EX1 STIM
EXCEPT 60'RASP WHEN 0 IS COURTED
BY OTHER Cfdi
Figure 7.




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290 Psyche
[September
suddenly oriented to her right side and chirped four times. She turned to face him and they exchanged antennal contact. She walked past him, circled clockwise and paused with her rear toward him. He ran to her front and mounted on her head. He then turned into the proper position on the female and copulated. The pair was in copulo for 23 minutes. This male seemed disoriented at first, and probably was not in full courting condition even though the female accepted him. However, the female seemed to be in a state of high receptivity and may have been soliciting courtship herself. After uncoupling from the male females of ten accept courtship and mounting by other males, but copulation has never succeeded during our observations, probably because the genital orifice is obstructed by the spermatophore. Under such conditions they dis- mount after fifteen seconds or so. Males, after they have copulated, are not usually responsive to females for 15 to 20 minutes but few males have been carefully observed in this condition. Unresponsive females show their lack of receptivity by (I) keeping closed the subgenital plate with no further evidence of resistance (2) lowering the wings over the genitalia, (3) raising the hind femora until they point forward above the head with the tibiae stretched out above the horizontal plane and slowly waving the tibiae up and down, sometimes increasing the frequency and decreasing the amplitude until the femora are vertical and tibiae flexed, (4) kicking the male off, (5) running away and (6) flying away. It is striking how effectively the tibia1 waving turns off the courtship. In the field (1963) we observed one persistent male who was kicked off vigor- ously by a female. He returned to court again and oriented in the premounting position at the rear of the female. But when she waved the hind tibiae, he backed off and ran in another direction, chirping about four times as he went. It is possible that this is a learned response, for we have viewed many such encounters in the laboratory among naive or previously deprived males. Male-Male Interaction
When males meet on the ground, after crepitating toward one another or during their ground level wandering, they pause at distances up to two feet apart and orient by one facing the other in an alert pose. They then crepitate, hop, spurt-run 01- walk to close proximity of each other. The approach is sometimes accompanied by chirping. Usually one (A) orients perpendicular to the side of the thorax of the other (B)) and touches it with the antennal tips. Then (B) responds with a flutter-rasp (Fig. 9) with one or both



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19691 JViiZey and W e y - Social Displays 291 legs, (A) answers and turns his body parallel to ( I3 ) , either facing the same or opposite direction. They then generate flutter-rasps in alternation three or four times. After this sequence, if they are facing in opposite directions they walk in opposite directions, and, a few inches apart, pause in an alert pose for up to several minutes. They then crepitate in opposite directions, one first and the other a second later. If they face the same direction, they may walk parallel and flutter-rasp in several sequences before parting. We have observed in the field and more often in the laboratory that the members of some pairs seem to be of equal aggressive strength and both try to point toward the other's side. As a result, they circle around a common center and rasp in continuous alternation. Such bouts sometimes result in an attempt of one male to mount the other. This is followed with kicking by the mounted male and biting the dorsal carina of the pronotum by the mounting one. If a male tries to court another male, the signals of the courting male are usually turned off in mid-sequence by a responding flutter-rasp by the courted male. The courting male answers with a flutter-rasp and normal male-male interaction proceeds. However, males de- prived of opportunities to court females for a few days will complete courtship and mount a vigorously rasping male. Indeed, the only response certain to be made by a male in copulo is a flutter-rasp, serving to "turn off" courtship by another male.