winter experiments since I never had more than 10 specimens.
The test loops were played for 2 min. to an individual.
The other individuals were covered v;ith a cardboard box to
isolate them from the extraneous movements and sounds of the
observer. The individual test was considered positive if
the fem.ale walked to the test-speaker end of the cage and
stayed there for at least 20 sec. The results of the test
sessions are shown fully in Table 12 and a}:)breviated in
Table 13.
Interestingly both continuous and discontinuous re-
cordings attracted summer and winter females equally, indi-
cating that the breaks throughout the sumjaer-group songs
and at the beginning of the winter-group songs are not
important for attraction.
Most interesting is that sessions 11-13 (Table 12) used
recordings of N. retusus at 31 and 32°C, resulting in a high
wingstroke rate that is comparable to N. triops at 25°C.
There was better attraction to these recordings than to
recordings of triops at higher and lower v;ingstroke rates,
suggesting that wingstroke rate is an important attraction
factor and that the wingstroke rate to which a female
33
responds is a function of aiubient temperature. During Aug.
in North Florida N. triops and N. retusus may be heard
singing near each other.
The highest percentage of success of phonotaxis for
summer group triops occurs in the wingstroke-rate range com-
parable to those found in the field (Fig. 3) ; hov/ever, the
females were prescreened for response to this rate. There-
fore the only sure conclusion is that summer females that do
respond to the sijmmer rates do not respond to rates that
deviate by more than 10-20%. On the other hand, the attrac-
tion of the winter diapausing group is about the same
throughout the wingstroke-rate range. In fact, two indi-
viduals (d and f) were attracted to the slowest and fastest
wingstroke rate (Table 13) . The large range of female-
attracting wingstroke rates may be adaptive since the winter
individuals in the field probably vary in adult age due to
microclimatic differences (teneral winter adults are found
from Aug. to Dec. in Gainesville). Also, the lack of pulse
rate specifically in the North Florida winter group would
not be as important as in the summer group when five other
species of Neoconocephalus can be heard within earshot of
singing N. triops . No other Neoconocephalus are singing in
North America at the same time the winter group are singing.
Factors permitting species-specific attraction in Neo-
conocephalus deserve more attention — particularly N. triops
with its generation differences in song. A good approach to
34
this problem involves more sophisticated electronic equip-
ment to reproduce the calling-song carrier frequencies.
Also surroundings where the phonotaxis takes place should
simulate field conditions since echoes in the small, low-
noise room m.ay have confused sound-orienting females. A
larger room would eliminate m.uch of the wall bumping which
probably hinders in-flight orientation. Perch sites such
as shrubs or grasses may be necessary for f emale-to-m.ale
orientation. Even considering the weaknesses of the experi-
ment, female-to-male phonotaxis seems to occur and it appears
that wingstroke rate is an important part of the process.
GEOGRAPHIC VARIATION
Introduction
Distributions of sound-producing insects are more
easily studied than those of most other insects once the
species-specific calling songs are identified. In fact,
songs that are loud to the human ear, such as those of N.
triops, may be heard 3 00 yards or more under optimum condi-
tions. By covering large areas in a car, the known ranges
of many species may be increased and new species may be
discovered by their different calling songs. As shown in
the previous section, diapausing and nondiapausing groups
of N. triops may be identified by song phrasing and by
collecting date.
Figure 1 shows the U.S. range of both generations.
T. J. Walker reported N. triops on the Caribbean Islands of
Hispaniola (Sept.), Puerto Rico (Jan., June), Jamaica (June,
Nov., July), St. Croix (Jan.), Grand Caym.an (June), and
Trinidad (June, July) . All specimens sang a discontinuous
"song identical to that of the summer generation found in
the United States.* In fact. Walker believes that the
discontinuous song may be heard in the West Indies year-round,
â– T. J. Walker 1973: personal communication.
35
36
Rehn and Hebard (1915) reported the southern range of
triops extended to Colombia, S. A. Hebard (1932) col-
lected many specimens from Mexico, and Ostmark* sent me
specimens from La Lima, Elonduras.
The known northern limit of summer populations is
represented, by one specimen I heard and collected in George-
town Co., South Carolina. The continuous-singing winter
generation, however, extends northv;ard to Southeast Ohio**
and southern New Jersey (Rehn and Hebard 1915) and as far
south as Big Pine Key, v/herc I heard and collected only a
few continuous-singing specimens.
Calling Song
As mentioned in the introduction, one of the most out-
standing differences betv/een the winter and sumuiicr genera-
tions is the difference in singing v/ingstroke rate. With
calling-song dimorphism unknown in insects, the difference
in song originally led me to believe that I v;as working with
two species.
I collected katydids in or near the survey areas and
recorded them in the low-noise room under controlled tempera-
tures. Songs of specimens that were recorded three weeks
beyond the collection data were disregarded in hopes of
minimizing age-dependent variation in wingstroke rate. Each
*H. W. Ostmark 1960: personal communication,
**T. J. Walker 197 3: personal communication.
37
point in Figs. 3-7 represents a different individual. Re-
cordings v/ere made in the laboratory under controlled tem-
peratures. Field recordings were excluded since the ambient
temperature of the singer often differed from the tempera-
ture at the recording site. All recordings were made on the
same Nagra III tape recorder.
The North Florida (Fig. 3) and Central Florida (Fig. 4)
graphs show a distinct difference in the pulse rates of the
winter and summer populations. In fact, these points coin-
cide closely with those found by Walker (1954) for Gaines-
ville, Florida, specimens. The differences in the wing-
stroke rates are attributable to diapause as shown in the
previous section. However, in the Keys (Figs. 5 and 6) the
wingstroke rates of the winter and fall generations approach
those of the summer generation, perhaps indicating less in-
tense diapause; i.e., a proximate cause for this phenomenon
is reduced selection for intense diapause in the Florida
Keys, where the winters are mild and suitable for nymphal
development. In colder areas (North and Central Florida) ,
only diapausing adults survive the winter, as shown pre-
viously. In these areas there must be selection for more in-
tense diapause and there are obvious differences in wing-
stroke rate between the diapausing and nondiapausing genera-
tion. In Jamaica (Fig. 7) no differences in population
38
density or v/ingstroke rate v/ere noted during field work in
Nov., June, and July.*
Figure 3 summarizes the wingstroke rates of all areas.
It is interesting to note that the rates of all the non-
diapausing populations are very similar regardless of geo-
graphy. Yet to the north (where the diapausing generation
is more pronounced than the nondiapausing) winter wingstroke
rates become progressively slower.
At first glance the adaptive significance of seasonal
differences in phrasing could be due to the presence of
other sympatric species of Neocono cephalus with wingstroke
rates similar to those of the summer group. Hovi/evor, in
the laboratory females from both groups are attracted
equally well to either the discontinuous or continuous song
(Tables 12 and 13). Also the faster summer wingstroke rate,
though differing from one sympatric species (N. retusus) ,
is closer to two other sympatric species (N. velox and N.
robustus ) . The only reason I can find for the song differ-
ences is that they are produced by the physiological changes
associated with diapause.
Life Cycles
Survey areas were laid out to determine seasonal changes
in relative singing densities within a given area and to dis-
cover geographical variation in life cycles. The songs of
'T. J. Walker 1973: personal communication
39
sound-producing insects may be used not only in determining
numbers and locations of singers but also in determining the
life stage, since only reproductively mature males sing.
Each survey area consisted of a circular walk or slow
speed drive (30 m.p.h.) beginning about 45 min. after sunset
in a convenient rural area. Since every area was different
in habitats and weather conditions, comparative data are more
revealing than absolute numbers. Surveys v/ere made monthly
except in Gainesville, where weekly surveys were conducted
(Fig. 1). For comparison, the weekly Gainesville graph
(Fig. 9) is abbreviated in Fig. 10 to correspond with the
monthly data from other locations. Also shown in Fig. 10
is an approximation of the singing season in Southeast Ohio,
inferred from weather data, and South Carolina, inferred
from North Carolina listening records by Fulton (1951) .
Figure 9 shows a two-year, weekly analysis of a pasture
locality near Gainesville, Florida. The peaks for each gen-
eration seem to coincide closely in the top two graphs. The
lower graph is the singing density of the winter generation
in a m.ixed hardwood hammock. The singing peak appears to be
later, which may be explained by delayed reproductive matura-
tion due to the shaded conditions in the forest understory.
Figure 10 indicates that northerly one-generation demes
give way to two-generation demes in North Florida. In the
Florida Keys three generations are likely, and continuous
breeding may occur in the Caribbean. As one travels south.
40
the winter (diapausing) generation is less prominent and
sings earlier. In fact, on Big Pine Key the continuous
winter song was heard on only three occasions and discon-
tinuous singing was heard all year (Fig, 10) . In the
tropics neither VJalker nor I have heard any continuous
singers; yet Walker has heard discontinuous singers on five
trips to the Caribbean (no trips were made during spring) .
Perhaps the Florida Keys represent a transition zone from
temperate to tropical climates, with decreased selection for
adult overwintering diapause and increased selection for con-
tinuous breeding. Perhaps overwintering adult diapause in
temperate areas evolved from tropical dry season diapause.
The tropical dry season and temperate winter seem, to
correspond (both seasons lacking green grass for nymphal
food) . Only adults survive the temperate winter (Table 2) ,
and possibly only adults survive the tropical dry season.
I found no evidence of adult diapause in the Florida Keys;
a few singing adults (Fig. 10) and nymphs were found there
year-round. flowever, a portion of the adults could have
diapaused during the cool (Dec. -Jan.) or dry (April-May)
seasons and I would not have detected it.
Both indoor- and outdoor-rearing experiments showed
that eggs from single females hatched over eight-v/eek per-
iods (Table 2) . Furthermore, field-collected early-instar
nymphs reared under the same conditions became adults as
much as seven weeks apart (Table 3) . With large variance
41
in dates of winter-adult mating, hatch, and rate of nymphal
development, one would expect some external stimulus as
photoperiod to synchronize singing and mating in their re-
spective seasons. Nymphal development time coupled with the
photoperiodic control of diapause and color explains the
geographical ranges and relative sizes of summer and winter
generations. Figure 11 is a hypothetical — yet I think
realistic — modification of Fig. 10. The katydids require
approximately four months of warm weather to develop from
the singing of their parents to the photoperiod-sensitive
last nymphal instars. The solid vertical line represents
the critical photoperiod that triggers the color and dia-
pause or nondiapause condition of the adult. The broken
vertical line represents the first killing frost that termi-
nates juvenile development. In Ohio (Fig. 11) there is not
enough developmental time from the first singing date to the
critical photoperiod line to allow for a nondiapausing
(summer) generation. Thus in the North, the life cycle is
strictly univoltine. In South Carolina, however, there is
just enough time from the beginning of the winter singing
to the critical photoperiod line to allow for a few summer
singers. The fate of the offspring of these sumjner singers
is unknown, but mcany are probably killed as in the Gaines-
ville rearing experiments. Most of the offspring of winter
singers go into diapause as adults and become winter-
generation triops . In Gainesville, Florida, the offspring
42
of first-half -of -the-v7inter singers have time to make the
summer generation while the later half are caught by the
short day and go into diapause. Most of the summer-generation
offspring become v/inter adults, although some are probably
killed by the cold. In other words, in Gainesville, Florida,
the heterovoltine condition exists.
The data from Central Florida and the Keys indicate two
or more generations in Central Florida and three generations
or possibly continuous breeding in the Florida Keys.
The life cycle of N. triops in the Florida Keys and the
tropics deserves further study. Particularly interesting is
whether or not diapause occurs and, if so, whether it is an
adaptation to cold or dry seasons. If tropical dry season
diapause does exist, the token stimulus that initiates dia-
pause is unknown.
43
Table 1. Hatch from winter adults placed in aquaria
on 5 March 19 68
Aquarium no.
Week of
2
6
7
7
14 April 1968
6
-
-
-
21
2
9
17
-
28
5
3
6
-
5 May 1968
-
-
6
-
12
-
-
16
-
19
-
-
2
-
26
-
-
-
2 June 1968
-
-
2
15
9
-
-
-
12
16
-
-
-
6
23
-
-
-
-
30
-
-
-
-
Total
13
12
49
33
Death date 20
June
12 June
11 May
*
F adult dates**
27
2
June
Aug.
(1)
(1)
27
27
June (2)
July (1)
25
5
Sept
Oct.
(1)
(1)
*Escaped 27 May 1968.
**Numbers in parentheses show number of adults maturing
within one week of the indicated date.
44
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45
Table 3. Maturation dates of field-collected, outdoor-
reared nymphs, Gainesville, Florida, 197 2
Nymph
S CO
llected
Adults reare
d
Dates
Number
Approximate
instar
Numb
Br Dates
Generation
(W or S)**
15 May
3
2
2
2 5 Juno
S
15 May*
6
1
1
2 July
S
20 May
5
1
2
16 July
s
22 May
5
2
+
3
1
2
16 July
25 July
s
s
27 May
7
1
1
27 Aug .
16 July
w
s
3 May
6
3
2
25 June
s
3 May
2
4
2
2 July
s
2 June
8
1
+
2
2
1
16 July
13 Aug.
s
w
2 June
8
3
+
4
1
1
1
25 June
9 July
20 Aug.
s
s
w
2 June
4
5
+
6
3
25 June
s
7 June
4
1
1
1
30 July
13 Aug.
s
w
7 June
3
3
2
1
2 July
9 July
s
s
14 June
5
2
1
2
23 July
30 July
s
s
14 June
5
4
1
1
2 July
9 July
s
s
14 June
4
5
+
6
3
1
2 5 June
2 July
s
s
2 2 June
6
3
2
16 July
s
46
Table 3 - (continued;
Nymph
S CO
llected
Adults rec
ared
Approximate
Generation
Dates
Number
instar
Numbe
r
Dates
(W
or S) **
22 June
7
1
1
1
23 July
10 Sept
S
W
22 June
5
5 + 6
4
2 July 1972
S
28 June
5
1 + 2
1
10 Sept
1972
S
28 June
5
3
1
2 Aug.
1972
w
7 June
-
-
-
14 July
-
-
-
24 July
-
-
-
8 July
6
4; 4 +
6
1
1
27 Aug.
3 Sept.
1972
1972
w
w
17 July
4
5
3
27 Aug.
1972
w
*A different collecting site is indicated by each line
for a given date.
**Determined by comparing the adult date with life stages
in the field. Adult molts after 10 Aug. v/ere considered too
late to tan and sing with the summer group.
47
Table 4. Color changes occurring during the ultimate
and penultimate molts of green, male n^inphs
Adult color Fat
Photoperiod Green Brown Songs heard conspicuous'
5
3**
5
7
3
7
*Fat completely lining the abdominal cavity obscuring
the viscera.
**Two green, one brown.
One individual turned brown during penultimate molt.
tt
Two individuals turned brown during penultimate molt,
A-Early summer
Natural
5
15 hr.
1
2
11 hr.
5
B-Late summer
Natural
7 +
15 hr.
1 1 v,>-
2
48
Table 5. Number and percentages of brov/n/green colored
morphs of N. triops collected in Alachua Co. during 1959-72
Males Females
Green Brov/n Green Brown
No. % No. % No. % No. %
Summer* 73 7 8 21 22 37 93 4 7
\^J„vTfr'^ 5 3 142 97 47 69 21 31
*1 July- 12 Aug.
**Dec. -Mav.
49
Table 6. Color of field-collected suramer- and winter-
generation nymphs collected in Gainesville from 1969-1971
Groups
Instars*"
No . brovm
No. green
Summer
1-3
4
5
6
41
14
13
18
Winter
1-3
4
5
6
1
13
63
22
29
28
*All n^TTiphs were reared outdoors to at least last
instar to determine if they belonged to the winter or sumraer
group.
**I never differentiated the early instar which may be
more or less than three.
50
Table 7. Sizes of early suramer gonads and accessory
glands of individuals reared under long-day, short-day, and
natural conditions
Photoperiod
Natural Long day Short day*
Testes
Dimeter (range in .01 nun.) 55-155 107-136 83-167
n 5 5 5
X 109 122 131
SD 38 13 36
Male assessory glands
Weight (range in mg . )
10-26
17-25
5-11
n
5
5
5
X
18
22
8
SD
7
3
3
Ovaries
Weight (range in mg.)
198-350
143-416
12-18
n
6
5
5
X
279
274
15
SD
56
102
3
*Fat conspicuous in all individuals in this column,
**Diameter = maximum diameter + minimum diameter.
51
Table S. Initial wingstroke rate and final wingstroke
rate of eight individuals recorded over a span of at least
six weeks
First song Last song Difference
96.0 93.0
97.0 92.0
102.0 94.0
103.0 90.0
104 .0 94 .0
104.0 99.0
101.0 96.0
100.0 90.0
X - 100.88 X = 93. 50
SD =3.04 SD = 3.02
*t = 6.5, p < . 001.
3
5
5
8
13
8.
5.
5.
10.
X =
= 7.
19
SD
''
.18
52
Table 9. Wingstroke rates of short-day (diapausing]
and long-day (nondiapausing) individuals reared from a
single collection of nymphs*
Diapausing group Nondiapausing group
104.0 105.0
98.0 116.0
95.0 110.0
96.5 110.0
112.0
106.0
X = 98.38 X = 109.30
SD -= 3. 95 SD - 4.02
*t = 4.42, p < .005.
53
4J
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(1)
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C
01
k tU
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m
fC
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â– H -H
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fe
s
IX
IT) tH og
VI M VI
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54
Table 11. Initial' songs of group C and the songs of
group A at the same time*
Group A Group C
98.0 101.0
13.5 103.0
98.5 101.5
103.0 103.0
X = 98.25 X = 102.13
SD = 3.8 8 SD - 1.03
â– t = 1. 95, p = 0.1
55
Table 12. Attraction of female N. trio ps at 25 ± 1°C
to recorded N, triops and N. retusus songs at 8 db
Wingstroke Continuous (C)
Test rate of or discontinuous No. of -^ No. of +
session tape (D) song tested** responsest
Summer group females
1
. 209
2
91
3
80
4
118
5
100
6
118
7
85
8
91
9
87
10
109
11*
114
12*
109
13*
113
14
109
15
128