GEOGRAPHIC VARIATION AND DIMORPHISMS IN SONG, DEVELOPMENT,

AND COLOR IN A KATYDID: FIELD AND LABORATORY STUDIES

(TETTIGONIIDAE, ORTHOPTERA)



BY

JAMES JUDD WHITESELL



A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS OF THE DEGREE OF
DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA
1974



ACKNOWLEDGiMENTS

I greatly appreciate the efforts of Dr. T. J. Walker,
chairman of. my supervisory cominittee, who was always will-
ing to relinquish his time to offer suggestions and give
advice concerning the research and preparation of this
dissertation. Travel expenses and graduate stipend were
provided by NSF Grant GB 20749.

Thanks are also extended to the members of my super-
visory committee, Drs. T. C. Emmel, D. H. Habeck, J. E.
Lloyd, and J. L. Nation, and to Dr. W. G. Eden, chairman of
the Department of Entomology and Neraatology.



PREFACE

My first encounter with the katydid Neoconocephalus
triops occurred on an unseasonably warm night in Feb. 1968.
I left my Gainesville apartment after supper to get a book
I had left in my car. While walking downstairs I saw
katydids on the ceiling of the front porch and flying around
the porch light. Once outside I saw others darting about
the street lights like sphingid moths. Most impressive was
that from every' large tree and many shrubs katydids were
making a continuous droning buzz much like a door buzzer.

I drove to some nearby pastures and counted 23 singing
males in 100 yards of roadside. Returning home, I received
a call from relatives 120 miles to the north in Georgia
asking me about the "noisy grasshoppers" on their screens
and shrubbery.

The next norning at school several people brought me
specimens and several more commented about the "racket the
previous night." One student complained that sleep was
impossible because one of "those things" was singing outside
his window on a bush. He threw hot water on the bush, but
was kept awake by other singers in the distance.

I compared my observations with those of Dr. T. J.
Walker, who had experienced this phenomenon before. Walker



said that such an eruption of katydids occurs every winter
in Gainesville. He noted that most of the singers found at
this time were brown, and told of a contrasting summer erup-
tion in which the katydids were mostly green and sang a
different song. Walker also noted that katydids in the
summier and winter groups were structurally identical.

We ended this conversation with a question that was to
reoccur in our discussions for the next four years: "Do
these two eruptions represent one or two species of
katydids?"



11

iii

vi



TABLE OF CONTENTS

ACKNOWLEDGMENTS

PREFACE

ABSTRACT

INTRODUCTION 1

STUDY OF GAINESVILLE POPULATIONS 7

Rearing 7

Photoperiodic Control of Color 11

Diapause ]_8

Causes of Seasonal Variation in Stridulatory

Wingstroke Rate 24

Orientation to Calling Songs 29

GEOGRAPHIC VARIATION 35

Introduction 35

Calling Song 36

Life Cycles 38

LITERATURE CITED 71

BIOGRAPHICAL SKETCH 7 5



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

GEOGRAPHIC VARIATION AND DIMORPHISMS IN SONG, DEVELOPMENT,
AND COLOR IN A KATYDID: FIELD AND LABORATORY STUDIES
(TETTIGONIIDAE, ORTKOPTEPJV)

By

Jaines Judd Whitesell

June 1974

Chairman: Thomas J. Walker

Major Department: Entomology and Nematology

Neoconocephalus triops (L.) is a species of copiphorine
katydid found throughout southern United States, the
Caribbean, and northern South America. It is a single
species, not two or more as previously thought. It is the
first example of age and of prior adult diapause affecting
singing wingstroke rate. It is the first tettigoniid known
to break diapause in response to photoperiod and the first
orthopteran known to have photoperiod-controlled brown/green
color dimorphism. It is the first case of clinal variation
in calling song. Furthermore the variation appears to be
environmentally induced rather than genetically based. Also
it is the first singing orthopteran (perhaps the first insect)
whose life cycle is known as it varies from univoltine in
the North to nonseasonal in the South. In some intermediate
areas, a winter generation gives rise to all of the follow-
ing summer generation and to some of the following winter



generation. The summer generation gives rise to the re-
mainder of the following winter generation.

Laboratory studies using live males showed that female;
came to calling males. Use of taped calling songs having
different wingstroke rates (since they were recorded at
different temperatures) suggested that wingstroke rate is
important in female attraction.



INTRODUCTION



Neoconocephalus triops (L.) is a name applied to cer-
tain katydids of the subfamily Copiphorinae . Unlike other
U.S. Neoconocephalus these katydids exhibit seasonal differ-
ences in color forms, acoustical signals, adult range, and
diapause. Such differences give new impetus to a 215-year-
old taxonomic question: Do these katydids represent one,
or more than one, species? If one species, then how are
differences in color, song, ranges, and diapause explained?
If more than one species, why are they not morphologically
distinguishable?

The taxonomic history of this katydid is one of nomen-
clatural chaos. Photographs of a specimen believed to be
the 1758 Linnaean-type of " Gryllus triops " from the "Indiis"
show clearly that it is not what is presently called Neocono -
cephalus triops .* Burmeister's 1838 description of Cono-
cephalus obtusus appears to be the current N. triops.*
Nomenclatural disorder was aggravated when specific epithets
were given to the color morphs , and sLmilar katydids from
different localities were given different names. Rehn and
Hebard (1915) concluded that the name Conocephalus fusco -
striatus Redtenbacher , 1891, and N. mexicanus var. tibialus



'T. J. Walker 1973: personal conmiunication .

1



Karny, 1907, had been given to the brown phase and G. triops
Linnaeus, 1758, C. obtusus Burraeister, 1838, C. dissii nilis
Serville, 1839, and C. raexicanus Saussure, 1359, had been
given to the green phase. Rehn and Hebard (1915) concluded
that all these names referred to a single species that should
be called N.. tr i_op_s . They mentioned color dimorphism but
failed to correlate it with season. They also speculated
that the species was two-brooded. Hebard (Rehn and Hebard
1915) noted seasonal differences in song intensity, but
failed to observe distinctive seasonal differences in song
phrasing. Subsequent interest in song variation continued
in spite of Mr. Rehn ' s warning concerning Hebard 's observa-
tion: "Such mistakes [referring to differences in song
noted by Hebard] are likely to occur in field observations
unless extreme care is exercised" (Rehn and Hebard 1915) .
Like many taxonom.ists , Rehn collected and worked mostly on
museum collections while abstaining from field observations
(which often reveal biological phenomena important to rec-
ognizing species) .

In the 1950s, Dr. T. J. Walker, a field biologist with
an interest in insect sound communication, began to study
" Neoconocephalus triops ." In Gainesville, Florida, he found
that year after year there were two distinct groups of
singers — one winter and one summer. Each group sang a dis-
tinctly different song. The summ^er song was a discontinuous
buzz, while the winter song started intermittentlv but



usually became continuous. Sonographic analysis (Walker
1964) of the sound pulses shov/ed that the surraner group had
a faster wingstroke rate than the winter group. This last
discovery seemed particularly significant in relation to
Walker's work on tree cricket calling songs (Walker 1957).
In species with continuous and broken trills (similar to
the songs of N. triop s) , sexually responsive females were
attracted to songs with a pulse rate approximating that of
the wingstroke of the conspecific males. Once calling song
had made an initial division possible, morphological differ-
ences that would have been overlooked without the song dif-
ference were discovered. Song analysis helped Walker find
many new species of sound-producing Orthoptera (Walker 1962,
1963, 1964, 1969, Alexander and Walker 1962, Walker and
Gurney 1960) .

In this manner, other workers also discovered additional
species. R. d. Alexander (1957) found that the common field
cricket of eastern United States was actually a complex of
at least five species, each with a different calling song.
More important, two other field crickets, G. pennsylvanicus
and G. veletis , even after being recognized as tv;o snecies,
were difficult to separate by morphology. The ranges and
calling songs are almost identical but pennsylvanicus over-
winters as an egg whereas veletis overwinters as a juvenile
so that the adults occur at different seasons (Alexander
and Bigelow 1960) . When adults of veletis and pennsylvanicus



were kept together in the laboratory, hybrids v;ere never
produced; yet hybrids can be produced under laboratory con-
ditions between other species of Gryllus with presuraably a
more distant common ancestry than that of G. pennsylvanicus
and G. veletis .

From previous studies of the significance of calling
songs and seasonally isolated populations, it seemed logical
that "N, triops " was actually tv/o species. Walker found
additional evidence to support the two-species concept.

1) Seasonal life history - With the summer group be-
coming adults and singing in early summ.er, it
appeared that they came from overwintering eggs
like the other 12 species of Neoconocephalus in
North America. The winter group, however, over-
wintered as an adult in diapause as does Pyrgo-
corypha uncinata (another katydid from the same
subfamily and similar range to N. triops ) . Breaking
of diapause was marked by singing during the first
warm nights of winter.

2) Brown-green color dimorphism — Summer males and
females were mostly green. Winter males were
mostly brown yet winter females were mostly green

(Table 5) . The occurrence of sex-biased color
dimorphism in only one group suggested separate
gene pools.



3) Differences in range - V7alker pointed out differ-
ences in the range of the two groups with the
adult overwintering group extending farther north,*

Based on the available evidence. Walker decided that in
Gainesville "N. triops " was two species. However, he was
not sure what was happening in South Florida. His data
were inadequate for him to decide whether one, tv;o, or three
species occurred in the Florida Keys. He speculated that
the two Gainesville species might merge into one in the
Florida Keys.

At the time of Walker's 1964 paper, the only evidence
for the one-species hypothesis was the lack of morphological
differences between the two groups in any one location and
an apparent breakdown in seasonal isolation on the Florida
Keys. Several students studied genitalia, stridulatory
files, and wing venations but failed to find any consistent
morphological differences between the two groups. The
fastigium (pointed part of the head often referred to as
cone) varied in size and shape geographically but not sea-
sonally.

Dr. Walker and I felt that extensive field studies,
outdoor rearing, and other experiments to vary environmental
parameters were needed to demonstrate whether or not the two
groups were genetically distinct and reproductively isolated
from one another. If the two groups had separate gene pools.



^Personal Communication, 1973,



then they should be considered separate species even though
they were morphologically identical. If, on the other hand,
they were found to share the same gene pool, they would be
one species with seasonally distinct mate recognition sig-
nals and v/ith sex-specific seasonal differences in the pro-
portions of -brown and green individuals. Neither situation
was known to have a parallel in sound-producing Orthoptera.
The answer to the question, "Does this represent one or two
species of katydids?" was sure to add new concepts to katydid
systematics and biology.



STUDY OF GAINESVILLE POPULATIONS
Rearing
Rearing experiments v;ere conducted to determine the
seasonal life history of the winter and summer groups. In-
door rearing was attempted to see if rearing from adult to
adult v/as possible. Outdoor rearing was conducted in con-
ditions as natural as possible to reveal the insects'
natural life cycle. To check the significance of outdoor
rearing results life history stages were monitored in the
field and field-collected nymphs were reared.

Indoor rearing began in March 1968. Virgin adults
collected as teneral adults in the fall and held until March
in one-quart Mason jars were put in 12 aquaria (1 pair/
aquarium) containing sterilized soil and freshly planted
bahia grass ( Paspalum notatum ) . The Mason jars and aquaria
were kept in a laboratory v/here photoperiod and temperature
were variable. The females laid eggs by inserting their
ovipositors into the soil and releasing one egg with each
insertion. [In the field I saw oviposition only twice. Each
time the ovipositor was placed between sheaths of Paspalum
urvillei (Vasey grass) . I suspect that this oviposition
process may be more frequent than soil oviposition.]

Hatching occurred in four aquaria as shown in Table 1.
Unfortunately most of the nymphs desiccated in a faulty



biocliraatic chamber, but a few matured to adults. Some
could have matured in time to mate in the summer group while
others took so long that they only could have mated in the
winter group. Though the katydids v;ere reared in an un-
natural environment, the temporal spread of offspring later
proved to be significant.

Initial field-rearing experiments vv'ere conducted in six
screen cages placed outdoors at the University of Florida's
farm known as the Honey Plant (hereafter called "Honey
Plant") . The cages were screen cylinders 24 in. in diameter
and 24 in. high with a flat screen top. The soil under each
cage was sterilized and planted with bahia seed. On 9 July
1968, six weeks after planting, two pairs of field-collected
summer adults were put in each cage. During one year of bi-
weekly inspections, the cages failed to yield any offspring.
The experiment was repeated beginning in June 1969 with 12
additional aluminum screen cages 16 in. in diameter, 24 in.
high, and crimped at the top. Again, no offspring were seen
during one year of biweekly inspections. Negative results
were perhaps due to egg desiccation by excessive heat since
the cages were exposed to direct sunlight.

Successful outdoor rearing began luring July 1971 at
two partially shaded sites. New recta.-.gular screen cages,
16 in. square at the top and bottom and 24 in. high were
framed with 1 x 2 in. lumber treated with copper arsenate.
A board frame was attached to the open bottom to extend the



cage 6 in. into the fumigated soil. Tv/elve cages were
placed in mesic hammock west of Gainesville and 15 under a
large live oak at the Honey Plant. Bahia seed v/ere planted
in advance to allov; a good stand of grass for oviposition
and food. Only teneral (virgin) adults were placed in the
cages. Hatching occurred in these cages and the nymphs were
transferred to screen-topped, one-quart Mason jars for
rearing to adulthood. These jars contained screen cylinders
for perching and molting and were kept under a screened
shelter at the Honey Plant to eliminate death from exposure
to sun and rain, yet allowing near-natural temperature and
photoperiod. A fev/ nymphs taken from the cages were reared
indoors to maximize chances of obtaining adults for song
assay, but ants killed these before they matured.

Summer-collected female adults gave rise to adults that
correspond to winter group adults (Table 2, rows 1 and 2).
During Sept. 1971 I placed 19 field-collected winter group
females and corresponding males in cages (Table 2, row 3).
They never produced offspring even though most of them lived
through April. On warm nights the same winter and spring I
collected 6 winter adult females. When put in cages they
produced offspring (Table 2, rows 4 and 5). It is note-
worthy that the 1 adult reared from the fem.ales introduced
20 Feb. matured in time to be in the summ.er group. Yet the
4 adults reared from females introduced 21 April became v/inter
adults even though they hatched only one to three weeks later



10



than the individual that became a sununer adult. If the fall-
collected adults (Table 2, row 3) had mated under caged
conditions at the time of first singing in the field (warm
nights in Jan.), many of the resulting offspring might have
become adults before the offspring from the female introduced
20 Feb. 1972 (Table 2, row 4). The importance of the varia-
tion in the adult dates of the summer generation will be ex-
plained in the next section. Slow (or late) growers of the
winter group died unless they became adults before 1 Jan.
Cold seems the most likely cause of death.

The important feature of Table 2 is that in Gainesville
the summer group gives rise to only the winter group, indi-
cating that the two groups are generations of the same gene
pool. Another important feature of Table 2 is that Gaines-
ville triops is neither entirely univoltine nor entirely
bivoltine but is both. Jackson and Peters (1963) refer to
this condition as heterovoltine.

Outdoor rearing of field-collected nymphs also indi-
cated that the offspring of at least some winter parents be-
come summer-group adults (Table 3) . The early-instar nymphs
collected in late spring and early summer (as early as 22
April 1971) which gave rise to summer adults could only have
come from the winter generation since outdoor rearing gives
no evidence of overwintering eggs. The later in summer that
early ins tars were collected, the greater the chance they
would become winter triops . First instars were collected as
late as 22 June 1972 (Table 3) .



11



Rearing experiments as well as the results of field
collections indicate that oviposition occurs over a long
(three-month) period. This may be partly due to the long
period of mating and oviposition extending from v/inter to
late spring. In fact I collected eight winter female adults
during June ,in lawns and fields in the Gainesville area (at
least one month after the last singing was heard) . One of
these females when put in an indoor aquarium oviposited for
five days before dying. Oviposition probably occurs through-
out the five-and-one-half month period that the active winter
adults are found in the field, thus contributing to the tem-
poral spread of hatching. The physiological basis of the
different growth rates of nymphs collected at the same time
and stage is unclear (Table 3) .

Mating of the winter generation starts in Jan. and ovi-
position extends through June, yet the summer group of re-
productives appears to be limited to July and early Aug.
The following two sections describe photoperiod experiments
that show how the switch from summer to winter generation
occurs within the common gene pool.

Photoperiodic Control of Color
Rearing evidence indicated one gene pool but left unex-
plained generation differences in song, diapause, and color.
I suspected photoperiod as an environmental cue determining
color because I found two green teneral males near a street
light in Sept. , when males under natural circumstances were
brown.



12



By placing photoperiod chanibers in a screened shed, I
was able to control photoperiod while maintaining near-
natural temperatures. The chambers measured 24 in. square
by 40 in. high and were constructed of 1/4-in. pl^'-z/ood,
lined with wall board, and illuminated internally by two
15-w fluorescent bulbs. T\s^o-inch air conditioner hoses
connected with a suction fan exhausted air from the chambers
keeping them within ± 1.5°C of ambient temperatures. Timers
controlled the day length at 15 hr. (long day) in one cham-
ber and 11 hr. (short day) in the other chamber. The early
July day length in Gainesville (30° N. latitude) is 14 hr.
57' (including civil twilight). The mid Dec. day length is
11 hr. 05' (including civil twilight). The two chambers
approximated these natural day lengths.

During Sept. 1968, four field-collected brown males,
two green females, and two brown females v;ere placed in each
chamber with dry dog food and water. These adults were ob-
served from Sept. 1968 to May 1969, but no color changes
occurred.

On 30 June and 1 July 1972 I placed field-collected last-
stage, male nymphs in individual Mason jars. All nymphs
found at this time in Gainesville were green. Five nymphs
were placed in each of the two chambers and five more were
placed next to the chambers in natural photoperiod (control) .
All nymphs became adults between 2 and 4 July (Table 4 , A) .



13



All adults v/ere dissected on 24 July 1972 to determine
the diapause state by reference to gonad size. Although
there was no significant difference in gonad size for the
three groups, fat tissue completely lined the abdominal
cavity of the 5 individuals from the short-day chaiohcr . Fat
was not at all conspicuous in any of the other 10 individ-
uals. Singing was heard from natural and long-day indi-
viduals but none from short-day individuals. In the field,
singing was abundant during the three weeks that the long-
day and control males were singing. The seasonal percent-
ages of the two color forms of field-collected adults are
different (Table 5) .

The 15 nymphs were summer-generation triops as indicated
by the control. However, individuals exposed to short days
behaved like the adult overwintering generation that occurs
in the field during late summer and fall. They molted to
brown adults, failed to sing, and had large quantities of
fat typical of winter triops as well as the only other local
adult-overwintering katydid, Pyrgocorypha uncinata . Long-
day and natural photoperiod individuals were like the summer
generation: green, without conspicuous fat, and producing
calling songs.

In order to test the effect of photoperiod on juveniles
that normally become winter adults, 24 green, late-instar
nymphs were collected between 15 Aug. and 1 Sept. 1973 and
randomly placed under the same conditions as described for



14



the previous experiment v/ith the summer generation. Four
nymphs died, and the rest molted to adults from 20 Aug. to
1 Oct. 1973 and were dissected three to eight weeks later
(Table 4, B). At least three singers were again heard from
the long-day chamber, but this time the control as well as
the short-day groups were silent. The results of the two
experiments (Table 4, A, B) were the same except for the
natural photoperiod groups which paralleled in coloration
the adults in the field. Also, two of the 15-hr. photo-
period group became brown. These two individuals were not
necessarily different from presumptive summer-generation
individuals in their response to photoperiod (Table 5) .

Under field conditions most color changes evidently
occurred during the later molts (Table 6) . Of nymphs reared
under natural photoperiods , only one individual of the
summer group changed color before the last molt (N=^96) .
Eight color changes (N=142) occurred before the last molt
in the winter group (one before the penultimate molt) . I
have never collected a brown early-instar nymph (n>300) or
observed a molt from brown to green in the laboratory
(n>1500) .

The day length for 15 Sept. in Gainesville (the week
that most of the nymphs in Table 4 molted to adults) is 13
hr. 11 min. (including civil twilight) or 1 hr. 46 min.
shorter than early July when m.ost of the summer generation
molt to adults.



15



Although the change in color is largely a photoperiod
effect, it was not ascertained whether the color response
was to a specific day length or to change (increase or de-
crease) in day length. Hov/ever, the latcer hypothesis in
its simplest form is refuted since nymphs in the natural
photoperiod â–  (decreasing) became green adults (Table 4).

I failed to find an exam.ple in the literature of photo-
periodic control of color in Orthoptera. Hovrever, one would
expect such color dim.orphism to be adaptive where bivoltinism
is combined with seasonal habitat changes. Most orthopteran
color changes occur with univoltine acridids in response to
temperature, humidity, crov;ding, and light-v/ave length and
intensity. Brown/green polymorphism is well documented in