Florida Entomologist 84(2)
A MORPHOLOGICAL MEANS OF DISTINGUISHING FEMALES
OF THE CRYPTIC FIELD CRICKET SPECIES, GRYLLUS RUBENS
AND G. TEXENSIS (ORTHOPTERA: GRYLLIDAE)
DAVID A. GRAY 14, THOMAS J. WALKER2, BRENDA E. CONLEY1 AND WILLIAM H. CADE1'3
1Department of Biological Sciences, Brock University, St. Catharines, Ontario, L2S 3A1, Canada
2Department of Entomology and Nematology, University of Florida, Gainesville, FL, 32611-0620, USA
3Present Address: The President's Office, The University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada
4Present Address: Department of Biology, The University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada
The field crickets Gryllus rubens Scudder and
G. texensis Cade and Otte (previously G. integer
from Texas, see Cade & Otte (2000)) are the most
commonly collected crickets throughout the
southeastern United States from North Carolina
to Texas. The two species are sympatric from
western Florida to eastern Texas (Walker 1998).
These two species are the only known trilling field
crickets in the southeastern US, and are cur-
rently separated by song differences alone. Male
G. rubens produce trilled calling song with pulse
rates averaging ca. 55 pulses per second (p/s) at
25C, whereas G. texensis produce trills with
pulse rates averaging about 80 p/s at 25C (Sour-
oukis et al. 1992, Walker 1998, 2000 Martinet al.
2000). The pulse rates of the two species become
more similar at lower temperatures, but provided
that the temperature is above approximately
20C, males can unambiguously be identified to
species by song (Walker 1998; Gray & Cade 2000).
No morphological means of distinguishing either
males or females has previously been reported
(see Nickle & Walker (1975) for other species of
the southern United States). Here we report that
most females of the two species can be separated
on the basis of body-size relative ovipositor
length: G. rubens have longer ovipositors relative
to body size than do G. texensis.
We compared the ovipositor lengths and the
pronotal widths of 122 females from several local-
ities across the species' geographic ranges. Fe-
males were either laboratory reared from field-
caught nymphs, laboratory reared offspring of
field-caught field-inseminated females, or were
field caught females. Females from allopatric
sites were identified to species on the basis of col-
election locality alone (G. rubens: Gainesville, FL
(n =15); G. texensis: Austin, TX (n = 14), Dallas,
TX (n = 6)) or based on the songs of their brothers
(G. texensis: Uvalde, TX (n = 2), Austin, TX (n =
1)). Females from sympatric sites (G. rubens: Mil-
ton, FL (n = 8), Marianna, FL (n = 12), Pensacola,
FL (n = 5), Mobile, AL (n = 1), Decatur, AL (n = 1);
G. texensis: Milton, FL (n = 32), Starkville, MS (n
= 9), Tuscaloosa, AL (n = 4), Pensacola, FL (n = 4),
Mobile, AL (n = 2), Carrollton, GA (n = 6)) were
identified to species based on the songs of their
The crickets were measured as two replicates;
replicates 1 and 2 represent crickets in the collec-
tions of DAG and the Florida State Collection of
Arthropods, Gainesville, respectively. The data
are presented together in Figure 1 and both sepa-
rately and pooled in Table 1. We found that female
G. rubens have ovipositors ca. 2.5 to 3 mm longer
relative to their body size than do female G. texen-
sis. For the pooled data, we tested the effect of
species with pronotal width as a covariate using
an ANCOVA. The model r' was 0.88 (i.e., 88% of
the variation in ovipositor length was accounted
for). Both species (F1,119) = 170.96, P < 0.0001) and
pronotal width (F1,119) = 440.93, P < 0.0001) were
significant predictors. A comparison of the slopes
of ovipositor length on pronotal width was made
by testing for a species x pronotal width interac-
tion in a separate ANCOVA. The slopes did not
differ (G. rubens, slope = 2.285, G. texensis, slope
= 2.374; F1,118) = 0.10, P < 0.7507). The intercepts
of the lines were 1.34 mm for G. rubens and -1.31
mm for G. texensis. Thus it should be possible to
separate accurately most females of these two
TABLE 1. MEAN +SD OVIPOSITOR LENGTHS (MM) OF G. RUBENS AND G. TEXENSIS.
Replicate G. rubens G. texensis t ,( P -value
1 14.42 + 0.79 (n = 24) 11.46 0.77 (n = 31) t (3) = 13.91 <0.0001
2 14.7 2.0 (n = 18) 11.2 2.4 (n = 49) t (65) = 5.53 <0.0001
Combined data 14.53 + 1.44 (n = 42) 11.30 1.91 (n = 80) t (120) = 9.60 <0.0001
A A AA 0o
A A A A 0
A A A
A A A A
A A A AA
A A A
3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
Pronotal width (mm)
Fig. 1. Ovipositor length as a function of body size (pronotal width) in Gryllus rubens (filled symbols) and G. tex-
ensis (open symbols). Triangles represent individuals identified to species based on the songs of their brothers,
whereas circles represent individuals identified to species based on locality alone. G. rubens have longer ovipositors
than G. texensis.
Females of the field crickets Gryllus rubens
and G. texensis can generally be distinguished on
the basis of their ovipositor length relative to
body size. G. rubens females have longer oviposi-
tors than do G. texensis.
CADE, W. H., AND D. OTTE. 2000. Gryllus texensis n. sp.:
A widely studied field cricket (Orthoptera; Gryllidae)
from the southern United States. Trans. Am. Ento-
mol. Soc. 126: 117-123.
GRAY, D. A., AND W. H. CADE. 2000. Sexual selection
and speciation in field crickets. Proc. Natl. Acad. Sci.
USA. 97: 14449-14454.
MARTIN, S. D., D. A. GRAY, AND W. H. CADE. 2000. Fine-
scale temperature effects on cricket calling song.
Can. J. Zool. 78: 706-712.
NICKLE, D. A., AND T. J. WALKER. 1975.A morphological
key to field crickets of Southeastern United States
(Orthoptera: Gryllidae: Gryllus). Florida Entomol.
SOUROUKIS, K., W. H. CADE, AND G. ROWELL. 1992. Fac-
tors that possibly influence variation in the calling
song of field crickets: temperature, time, and male
size, age, and wing morphology. Can. J. Zool. 70: 950-
WALKER, T. J. 1998. Trilling field crickets in a zone of
overlap (Orthoptera: Gryllidae: Gryllus). Ann. Ento-
mol. Soc. Am. 91: 175-184.
WALKER, T. J. 2000. Pulse rates in the songs of trilling
field crickets (Orthoptera: Gryllidae: Gryllus). Ann.
Entomol. Soc. Am. 93: 565-572.