Description of the Immature and Adult Stages of Ectatomma vizottoi (Formicidae: Ectatomminae)

Abstract

We estimated the number of larval instars of the ant Ectatomma vizottoi (Ectatomminae), by measuring the maximum width of the head capsules of 208 larvae and the morphology of the immature stages (eggs, larvae and pupae) and adults. There are three larval instars during the post-embryonic development. The reproductive eggs are dark brown. Hairs are present beginning with the first instar, are uniformly distributed over the larval body, and do not vary in length in the three instars. Pupae are protected by a light-brown silk cocoon. Adults of the worker and queen castes can be differentiated by size.

Full text

Description of the Immature and Adult Stages of
Ectatomma vizottoi (Formicidae: Ectatomminae)
by
Alexsandro S. Vieira1, William F. Antonialli-Junior1,2*, Wedson D. Fernandes1,3,
Viviane C. Tofolo4 & Edilberto Giannotti4
ABSTRACT
We estimated the number of larval instars of the ant Ectatomma vizottoi
(Ectatomminae), by measuring the maximum width of the head capsules of 208
larvae and the morphology of the immature stages (eggs, larvae and pupae) and
adults. ere are three larval instars during the post-embryonic development.
e reproductive eggs are dark brown. Hairs are present beginning with the
rst instar, are uniformly distributed over the larval body, and do not vary in
length in the three instars. Pupae are protected by a light-brown silk cocoon.
Adults of the worker and queen castes can be dierentiated by size.
Keywords: ants, cephalic capsule, Dyar’s rule, larval instars.
INTRODUCTION
e exoskeleton of insects made possible their evolutionary success in the
terrestrial environment. Among many important physical characteristics of the
exoskeleton is its rigidity and impermeability. e presence of the exoskeleton
determines a dierent form of growth from vertebrates. e principal growth
mechanism of insects is marked by a series of molts or ecdyses, which are
preceded by a period of intense growth and subsequently by a period where
the insect rarely increases its body size (Wigglesworth 1972). According to
Dyar’s rule (Dyar 1890), the cephalic capsule of larvae and caterpillars grow
1Programa de Pós-graduação em Entomologia e Conservação da Biodiversidade, Universidade Federal
da Grande Dourados.
2Laboratório de Ecologia, Centro Integrado de Análise e Monitoramento Ambiental, Universidade
Estadual de Mato Grosso do Sul.
3Faculdade de Ciências Biológicas e Ambientais, Universidade Federal da Grande Dourados;
4Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista (UNESP),
Campus de Rio Claro.
*Correspondence: William F. Antonialli Junior, Centro Integrado de Análise e Monitoramento
Ambiental, Universidade Estadual de Mato Grosso do Sul, Rodovia Dourados Itahum Km 12, Cidade
Universitária, 79804-970, Dourados, MS, Brazil. E-mail: williamantonialli@yahoo.com.br
27

28 Sociobiology Vol. 53, No. 1, 2009
arithmetically, increasing in width at each change of instar, at a constant and
specic rate in the interval from 1.1 to 1.9 mm, with a mean of 1.4 mm. In
the insects, in general, the number of larval instars can vary from three to 40,
and in Hymenoptera can range from three to six (Sehnal 1985; Chapman
1998). In the ants, the number of instars ranges from three to six (Masuko
1990), most oen with four instars (Hölldobler & Wilson 1990), and, rarely,
six instars (Masuko 1990).
e distinction and description of the larval instars are oen prerequisites
for ecological investigations of social insects, such as studies of colony de-
velopment for analysis of age distribution (Masuko 1990). Many studies of
the number of larval instars of ants have been conducted on species belong-
ing to two more-derived subfamilies, the Myrmicinae and the Formicinae
(Masuko 1990). For the poneromorphs, studies have concentrated on the
following species: Amblyopone silestri, an Amblyoponinae (Masuko 1990),
Ectatomma planidens, mistakenly identied as E. edentatum, an Ectatomminae
(Antonialli-Junior & Giannotti 2000), and in the Ponerinae, Pachycondyla
(= Brachyponera) chinensis studied by Masuko (1990), P. villosa by Zara &
Caetano (2001) and Odontomachus haematodus ( = haematodes) by Colombel
(1978).
In lateral view, the larva of poneromorphs shows the thorax and part of
the abdomen elongated and a “chest” folded ventrally, with the rest of the
ventral prole straight and dorsally convex, and rounded in the caudal region.
e prole of the larva varies little among species of the same genus, and the
pupae are generally covered by a cocoon made of silk produced by the larva
itself (Wheeler & Wheeler 1979).
ere are only two published studies, one with E. opaciventre (Antonialli-
Junior & Giannotti 1997) and the other with E. planidens, mistakenly identi-
ed as E. edentatum (Antonialli-Junior & Giannotti 2001), that describe the
morphological dierentiation between workers and queens; the workers are
signicantly larger. In this context, the objective of the present study was to
describe the immature stages and the morphometric dierentiation between
the worker and queen castes, as well as the males of Ectatomma vizottoi Almeida
(1987), a species of ant belonging to the subfamily Ectatomminae, a group
of the poneromorph subfamilies which occurs throughout the Neotropical
region (Bolton 2003).

29
Vieira, A.S. et al. — Immature and Adult Stages of Ectatomma vizotti
MATERIAL AND METHODS
Adult and immature individuals from eight colonies of E. vizottoi were col-
lected during the period from November 2004 through August 2006, on the
campus of the State University of Mato Grosso do Sul (UEMS), Dourados, MS
(22º13’16”S; 54º4820”W). e subterranean nests were excavated according
to the method described by Antonialli-Júnior & Giannotti (1997).
Immature stages
With the aid of a stereomicroscope, the length and diameter of 44 eggs
(1 ocular unit equal to 0.20 mm) and 50 pupae (1 ocular unit equal to 1.0
mm) were measured. To determine the number of larval instars, the width of
the cephalic capsule of 208 larvae was measured (1 ocular unit equal to 0.20
mm), and Dyar’s rule was applied (Dyar 1890). e means of the dierent
larval groups were analyzed by Tukey test (Parra & Haddad 1989), consider-
ing each group as one instar.
Morphological dierentiation of castes
e maximum length of the head; length of the antennal scape, length of
the anterior end from the pronotum to the posterior part of the propodeus
(i.e., the mesosome) and the maximum width of the second gastral tergite
of 96 adult individuals (9 queens, 57 workers and 30 males) were measured.
e measurements were made with the aid of a stereomicroscope tted with
an ocular reticule (1 ocular unit equal to 0.1 mm). e data were analyzed
by means of Student’s t test for unequal samples, with a signicance level
of p<0.05, between the means of the measurements of the queens and the
workers. Later, the immature and adult specimens were drawn, in order to
illustrate the morphological dierences between them.
RESULTS
Immature stages: eggs
e eggs of this species are elongated and ellipsoid in form (Fig. 1a). e
coloration of the reproductive eggs varies from very dark brown to nearly
black. e mean length is approximately 1.361 ± 0.004 mm, and the median
diameter is 0.768 ± 0.003 mm.

30 Sociobiology Vol. 53, No. 1, 2009
Immature stages: larvae
e larvae of E. vizottoi show the typical pogonomyrmecoid prole (Figs.
1 b-d), white-colored and with numerous hairs or tubercules, as well as
strongly sclerotized brown mandibles, and one pair of teeth beginning with
Fig. 1. Immature stages of Ectatomma vizottoi. a, Egg (same scale as lateral view of larvae); b, c, d,
lateral view of 1st, 2nd and 3rd larval instar, respectively; e, f, g, frontal view of head of 1st, 2nd and
3rd larval instar, respectively; h, frontal view of head of a pupa; i, lateral view of a pupa. Drawings
by Jaime R. Somera.

31
Vieira, A.S. et al. — Immature and Adult Stages of Ectatomma vizotti
the rst instar, with no evidence of morphological changes during the entire
development (Fig. 1e-g).
e mean width of the cephalic capsule was 0.20 ± 0.028 mm for the rst
instar, 0.28 ± 0.057 mm for the second, and 0.38 ± 0.071 mm for the third
(Table I). e slopes of the frequency-distribution curve for cephalic capsule
width indicate the existence of three distinct peaks (Fig. 2). is suggests the
occurrence of three possible larval instars. e estimated growth rate varied
from 1.3 to 1.4 mm in the width of the cephalic capsule of the larvae from
instar to instar (Table 1).
Instar Amplitude (mm) Frequency Mean width (mm) SD (mm) Growth rate Mean growth rate
1st 0.180-0.220 28 0.200 0.028 - -
2nd 0.240-0.320 106 0.280 0.057 1.400 1.387
3rd 0.340-0.440 74 0.385 0.071 1.375 -
Table 1. Mean cephalic capsule width (mm) of Ectatomma vizottoi larvae and the growth rate of the
larval instars.
Fig. 2. Frequency distribution of the cephalic capsule widths (mm) of Ectatomma vizottoi larvae.
Table 2. Tukey's test applied to the mean values for the three instars detected in
Ectatomma vizottoi. *P value signicant
Larval instar Mean (1) Mean (2) Mean (3)
0.200 0.280 0.385
1 - 0.0464* 0.0004*
2 0.0464* - 0.0051*
3 0.0004* 0.0051* -

32 Sociobiology Vol. 53, No. 1, 2009
e growth rate of the cephalic capsule was 1.4 mm from the rst to the
second instar, and 1.375 mm from the second to the third; the mean growth
rate of the species was 1.387 mm (Table 1). Tukey's test indicated signicant
Fig. 3. ueen of Ectatomma vizottoi. a, Frontal view of head; b, Lateral view of body. Drawn by Jaime
R. Somera

33
Vieira, A.S. et al. — Immature and Adult Stages of Ectatomma vizotti
dierences among the means of the three groups (Table 2), thus conrming
the existence of three instars during the larval development of this species
(Figs. 1b-g).
Fig. 4. Worker of Ectatomma vizottoi. a, Frontal view of head; b, Lateral view of body. Drawn by
Jaime R. Somera

34 Sociobiology Vol. 53, No. 1, 2009
Immature stages: pupae
e pupae (Fig. 1h-i) of E. vizottoi were surrounded by a light-brown silk
cocoon. eir mean length was 9.450 ± 2.887 mm, and mean diameter 4.13
± 0.274 mm.
Fig. 5. Male of Ectatomma vizottoi. a, Frontal view of head; b, Lateral view of body. Drawn by Jaime
R. Somera

35
Vieira, A.S. et al. — Immature and Adult Stages of Ectatomma vizotti
Morphological dierentiation of castes
e queens are perceptibly larger than the workers (Figs. 3 and 4). ey
possess wings (which are lost aer mating, with only alar scars remaining
beneath the tegulae), three ocelli between the compound eyes, and a more
developed abdomen compared to the workers (Figs. 3a and b).
All the morphological measurements analyzed showed signicant dif-
ferences between workers and queens. e maximum length of the head
showed a mean of 2.20 ± 0.16 mm in workers and 3.09 ± 0.12 mm in queens
(t=18.59; p=0.000). e mean length of the antennal scape was 3.18 ± 0.25
mm in workers and 3.51 ± 0.24 mm in queens (t= 3.688; p= 0.002). e
mean mesosome length was 5.17 ± 0.25 mm in workers and 7.08 ± 0.40 mm
in queens (t= 13.593; p= 0.000). e maximum width of the second gastral
tergite was 2.43 ± 0.19 mm in workers and 4.02 ± 0.34 mm in queens, a
highly signicant dierence (t= 13.440; p= 0.000).
In males (Fig. 5a and b), the mean maximum head length was 1.75 ± 0.13
mm, the mean antennal scape length was 0.47 ± 0.06 mm, the mean meso-
some length was 5.26 ± 0.23 mm and the maximum width of the second
gastral tergite was 2.18 ± 0.09 mm.
DISCUSSION
e eggs of E. planidens (Antonialli-Junior & Giannotti 2000) have the
same form as E. vizottoi, but with a dierent color, light brown. e dark
color pattern of the reproductive eggs is similar to the eggs of E. tuberculatum
studied by Hora et al. (2007). However, the same whitish color pattern of
the trophic eggs is observed in all three of these species.
e coloration of the larvae is similar to that of the majority of the larvae
of Hymenoptera, and the morphology is in accord with the description of
Wheeler and Wheeler (1971, 1979). Antonialli-Junior & Giannotti (2000)
also described numerous hairs or tubercules and sclerotized mandibles in the
larvae of E. planidens.
For the larval instars, the estimated growth rate varied from 1.3 to 1.4 mm
in the width of the cephalic capsule of the larvae. is accords with Dyar’s
rule, which proposes a variation from 1.1 to 1.9 mm (Dyar 1890). Antonialli-
Junior & Giannotti (2000) found that this rule also applies to the growth
rates of larvae of E. planidens.

36 Sociobiology Vol. 53, No. 1, 2009
ree larval instars were also found during the larval development of E.
planidens (Antonialli-Junior & Giannotti 2000). Masuko (1990) observed ve
larval instars for A. silestri, whereas for P. ( = Brachyponera) chinensis (Masuko
1990), O. haematodus (=haematodes) and P. villosa (Zara & Caetano 2001),
four instars were observed. erefore, in the poneromorphs, the number of
instars during larval development can range from three to ve, similar to
the Formicinae, and in the Myrmicinae from three to six. However, in the
Ecitoninae there appears to be no variation: Masuko (1990) studied three
species of this subfamily and observed ve larval instars in all of them.
e morphological characteristics of the pupae of this species are similar
to those described by Wheeler & Wheeler (1979), who reported that the silk
cocoon makes possible the emergence of the adult without the aid of work-
ers. In E. planidens (Antonialli-Junior & Giannotti 2000) and E. vizottoi,
the pupae are also protected by a cocoon, diering, for example, from the
Myrmicinae Solenopsis, in which the pupae are of the exarate type, or naked
(Hölldobler & Wilson 1990).
Signicant morphometric dierences between queens and workers have
been found in other species of the same genus, such as E. planidens (Antonialli-
Junior & Giannotti 2001) and E. opaciventre (Antonialli-Junior & Giannotti
1997). Prominent among these dierences are the larger gaster and second
gastral tergite of the queens. is may be due to a greater development of the
ovaries, which contain a larger number of ovarioles in relation to the work-
ers. In colonies of E. vizottoi, workers possess one or two ovarioles and the
queens have as many as 12 (Vieira et al. 2008). E. brunneum also possesses
one or two ovarioles per worker, and the queen has up to 15 (Toledo-Mello &
Caetano 1980). e dimorphism between queens and workers of E. vizottoi
is obvious, as also described by Antonialli-Junior & Giannotti (1997) in E.
opaciventre, by Lachaud et al. (1999) in E. ruidum, and by Antonialli-Junior
& Giannotti (2001) in E. planidens. In the case of E. ruidum, there is more
than one kind of queen, which the authors termed macro- and microgynes
(Lachaud et al. 1999).
e coloration of the workers and queens accords with the description
by Almeida (1987). e females of E. vizottoi are predominantly yellow-
brown, with a rust-colored gaster. e males are perceptibly smaller than
the workers and queens, with a small head and antenna constituted of 13

37
Vieira, A.S. et al. — Immature and Adult Stages of Ectatomma vizotti
elongated segments, whereas the antennae of workers and queens possess 12
segments. In addition, the body coloration of the males is darker than that
of the females.
In conclusion, E. vizottoi has three larval instars, which do not show marked
morphological changes during their development. e reproductive eggs are
dark, the trophic eggs are whitish, and the pupae are surrounded by a light-
brown silk cocoon like the other species of the genus. e queens dier from
the workers in size, as well as the presence of wings (or alar thecae, aer the
loss of the wings), of the tegulae and of the ocelli on the top of the head. e
males are quite distinct from the females.
ACKNOWLEDGMENTS
Our thanks to the researcher Jacques Hubert Charles Delabie of the
Laboratório de Mirmecologia of the Centro de Pesquisas do Cacau (Ceplac-
Ilhéus, BA), for identifying the specimens; to the artist Jaime Roberto
Somera, Departamento de Zoologia, Instituto de Biociências, Universidade
Estadual Paulista (UNESP); to the researcher Riviane R. Hora for revising
this manuscript; to FUNDECT for nancial support of the project (Process
No. 23/200.085/2007) and to Capes for awarding a master’s degree fellow-
ship to the rst author.
REFERENCES
Almeida, A.J. 1987. Descrição de seis fêmeas do gênero Ectatomma Smith, 1858 (Hymenoptera,
Formicidae, Ponerinae). Anais Sociedade Nordestina Zoologia 1: 175–183.
Antonialli-Junior, W.F. & E. Giannotti 1997. Nest architecture and population dynamics of
the Ponerinae ant Ectatomma opaciventre Roger (Hymenoptera: Formicidae). Journal
of Advanced Zoology 18: 64-71.
Antonialli-Junior, W.F. & E. Giannotti 2000. Imature stages of workers of Ectatomma
edentatum Roger, 1863 (Hymenoptera, Formicidae). Revista Brasileira de Zoociências
2(2): 105-113.
Antonialli-Junior, W.F. & E. Giannotti 2001. Nest architecture and population dynamics
of the Ponerinae ant Ectatomma edentatum (Hymenoptera, Formicidae). Sociobiology
38: 1-12.
Bolton, B. 2003. Synopsis and Classication of Formicidae. e American Entomological
Institute 71: 1-370.
Chapman, R.F. 1998. e insects: structure and function. Cambridge University press,
Cambridge. 770p.

38 Sociobiology Vol. 53, No. 1, 2009
Colombel, P. 1978. Biologie d’Odontomachus haematodes L. (Hym. Form): determinisme
de la caste femelle. Insectes Sociaux 25(2): 141-151.
Dyar, H.G. 1890. e number of molts of lepidopterous larvae. Psyche 5: 420-422.
Hölldobler, B. & E.O. Wilson 1990. e Ants. Harvard University Press, Cambridge, UK,
732 pp.
Hora, R.R., C. Poteaux, C. Doums, D. Fresneau & R. Fénéron 2007. Egg Cannibalism
in a Facultative Polygynous Ant: Conict for Reproduction or Strategy to Survive?
Ethology 113: 909-916.
Lachaud, J.-P., A. Cadena, B. Schatz, G. Pérez-Lachaud & G. Ibarra-Núñez 1999. ueen
dimorphism and reproductive capacity in the ponerine ant, Ectatomma ruidum Roger.
Oecologia 120: 515-523.
Masuko, K. 1990. e instar of the ant Amblyopone silestri (Hymenoptera: Formicidae).
Sociobiology 17(2): 221-244.
Parra, J.R.P. & M.L. Haddad. 1989. Determinação do número de ínstares de insetos.
Piracicaba, FEALQ, 49p.
Sehnal, F. 1985. Growth and life cycles. In: Kerkut, G.A. & L.I. Gilbert (eds.), Comprehensive
Insect Physiology, Biochemistry and Pharmacology. Pergamon. p 1-86.
Toledo-Mello, L.V. & F.H. Caetano 1980. Padrões morfológicos do ovário de formigas
Ectatomma quadridens (Hymenoptera: Ponerinae) e suas implicações funcionais. Rio
Claro, 16p. (Trabalho de formatura – UNESP, Rio Claro, SP).
Wheeler, G.C. & J. Wheeler 1971. Ant larvae of subfamily Ponerinae: second supplement.
Annals of the Entomological Society of America 64(6): 1197-1217.
Wheeler, G.C. & J. Wheeler 1979. Larvae of the social Hymenoptera. In: Hermann, H. R.
(ed.). Social Insects, lst ed. New York, Academic Press. p. 287-338.
Wigglesworth, V.B. 1972. e principles of insect physiology. John Wiley & Sons. New
York. 827p.
Zara, F.J. & F.H. Caetano 2001. Number of larval Instars of the Pachycondyla (=Neoponera)
villosa (Formicidae: Ponerinae): Determined by the Rule of Dyar. Sociobiology 37(3b):
679-686.