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Reproductive biology in three species
of the genus Onitis Fabricius 1798
(Coleoptera Scarabaeidae Onitini)
C. Palestrini a , E. Barbero b , E. Trevisan b & L. Borghesio c
a Dipartimento di Scienze e Tecnologie Avanzate , Università del
Piemonte Orientale , Corso T. Borsalino 54, 15100 , Alessandria ,
Italy
b Dipartimento di Biologia Animale e dell'Uomo , Università di
Torino , Via Accademia Albertina 17, 10123 , Torino , Italy
c Department of Ornithology, National Museum of Kenya ,
Nairobi , Kenya
Published online: 30 Jul 2012.
To cite this article: C. Palestrini , E. Barbero , E. Trevisan & L. Borghesio (2002) Reproductive
biology in three species of the genus Onitis Fabricius 1798 (Coleoptera Scarabaeidae Onitini),
Tropical Zoology, 15:1, 97-103, DOI: 10.1080/03946975.2002.10531168
To link to this article: http://dx.doi.org/10.1080/03946975.2002.10531168
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Tropical Zoology 15: 97-103, 2002
Reproductive biology in three species
of the genus Onitis Fabricius 1798
(Coleoptera Scarabaeidae Onitini)
1
2
2
3
C. PALESTRINI , E. BARBERO , E. TREVISAN and L. BORGHESIO
1 Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale,
Corso T. Borsalino 54, 15100 Alessandria, Italy
2 Dipartimento di Biologia Animale e dell’Uomo, Università di Torino, Via Accademia
Albertina 17, 10123 Torino, Italy
3 Department of Ornithology, National Museum of Kenya, Nairobi, Kenya
Received 19 March 2001, accepted 11 April 2002
The reproductive biology of three species of the genus Onitis Fabricius
1798 was studied in laboratory conditions. The species, O. belial (Fabricius 1789)
from Morocco, O. anthracinus Felsche 1907 and O. vanderkelleni Van Lansberge
1886 from Kenya, adopted a tunneler nesting strategy, as is typical of the tribe
Onitini. Nevertheless, the same species can adopt different tactics, modifying the
shape and depth of the nest, number of brood-masses per couple, and number of
eggs laid. However, this study showed that O. vanderkelleni builds a poorly elabo-
rated nest and lays a higher mean number of eggs, while O. belial and O.
anthracinus expend a larger amount of energy in the construction of the nest,
while reducing the number of eggs laid.
KEY WORDS: dung beetles, nesting behaviour, Afrotropical Region, Oriental
Region, Palaearctic Region.
Introduction
Material and methods
Results
Discussion
Acknowledgements
References
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INTRODUCTION
The genus Onitis comprises over 150 coprophagous species distributed in the
southern Palaearctic and Afrotropical and Oriental regions. Very little information,
on no more than 15 species, is available on the reproductive biology of this genus.

98
C Palestrini et alii
These data (HALFFTER & EDMONDS 1982, KLEMPERER 1982, ROUGON & ROUGON 1982,
EDWARDS & ASCHENBORN 1987, HALFFTER 1997) show that Onitis can have extremely
diverse behaviours, allowing a single species to adopt several different nesting tac-
tics in response to variable environmental pressures (ROUGON & ROUGON 1982). The
species adopt strategies characterised by a low level of behavioural stereotypy, a
case that is rarely found in the coprophagous Scarabaeidae.
In order to increase our knowledge of this little-known subject we studied the
reproductive biology of three species: Onitis belial (Fabricius 1789) (Fig. 1), O.
anthracinus Felsche 1907 and O. vanderkelleni Van Lansberge 1886.
Fig. 1. — Facies of an adult male individual of Onitis belial.

Reproductive biology in Onitis species
99
MATERIAL AND METHODS
Five males and 5 females of O. belial (collected in May 1999 in the Moroccan High
Atlas: Tizi-n-Tichka, 2200 m, and Oukamaiden, 1800 m), 4 males and 3 females of O. anthrac-
inus, and 2 males and 1 female of O. vanderkelleni (both collected in May 1999 in northern
Kenya: Poro, 2400 m) were brought to the laboratory where they were kept in couples at con-
stant temperature (20 °C). In keeping with previous experience, cages (n = 8) were built with
trunco-conical plastic containers, 24 cm maximum diameter and 22.5 cm high. These con-
tainers were cut into two symmetrical halves, easily separable to allow periodic (weekly)
checks. Each cage was filled with about 18 cm of sandy loam and closed at the top with a
fine-mesh net to prevent the escape of insects.
At weekly intervals we provided each couple of insects with fresh bovine dung and
removed dry residues of dung from the cage.
All measurements are given plus or minus Standard Deviation.
RESULTS
Our work showed that (Fig. 2): after a short period of acclimation, all species
started to feed and subsequently began digging in the soil.
The digging, aimed at nesting, was done under (n = 18) or, more rarely (in O.
belial, n = 2), just beside the dung. Tunnels were vertical (Fig. 2a) or oblique with a
Fig. 2. — Behavioural patterns in the nesting behaviours of three species of Onitis. Empty circles:
O. belial; filled circles: O. anthracinus; filled squares: O. vanderkelleni. Large symbols indicate the
preferred behaviour, while small ones mark the less common tactics.

100
C Palestrini et alii
diameter of 2 0.6 cm in O. belial, 1.5 0.6 cm in the other species. Differences in
tunnel diameter seem clearly related to differences in average adult size of the
three species, as O. belial adults are approximately 1/3 larger than adults of the
other two species. Each tunnel ended in a nest (Fig. 2b): in the case of O. belial, at
the bottom of the cage (n = 7) or at depths varying from 1 to 7 cm (n = 4) under
the soil surface. O. anthracinus nests were always found at the bottom of the cage
(n = 6), while those of O. vanderkelleni were located at the bottom (n = 1) or at
depths varying between 3 and 5 cm (n = 2).
The nest was made of a dung mass, the “cake”, poorly or not differentiated
into brood-masses (Fig. 2c-d). The cakes contained eggs and larvae irregularly scat-
tered in the dung. In other cases nests were made of several oblong “sausages”
(brood-masses), lying in the same horizontal plane and very close to each other
(Fig. 2e). In all three species, each brood-mass was made of worked dung laid by
the adult female in successive hemispherical layers. Between one and four eggs
were found in each brood-mass. Both cakes and brood-masses were housed in rudi-
mentary nest chambers dug at the end of the galleries or were simply placed within
the soil. In one case (O. belial) we found brood-masses inside a fibrous undifferen-
tiated dung clump.
The mean number of brood-masses per couple was 4.6 2.3 in O. belial, 6.1
2.7 in O. anthracinus; only once we found 3 true brood-masses in O. vanderkelleni.
Brood-mass measurements were: length 8.6
3.7 cm, width 3.0
0.4 cm in O.
belial; length 7.1 1.3, width 2.2 0.2 in O. anthracinus; length 5.8 0.3, width 2.7
0.3 in O. vanderkelleni.
O. anthracinus brood-masses were always tightly packed at the bottom of the
cage. On two occasions we found an undifferentiated cake from which incomplete
brood-masses (containing eggs) departed; in both cases the female was dead when
the cage was checked. We hypothesise that this could be an intermediate stage
between the preparation of the cake and its shaping into brood-masses. It is very
interesting that this seems to occur after egg laying.
O. belial seems to prefer preparing brood-masses (n = 8), while on only three
occasions we found undifferentiated cakes: in one of these the cage was checked
after the death of the adults, so the female may not have had sufficient time to
complete the construction of her nest. On a second occasion, half of the cake was
made of worked dung (with three eggs), while the rest was undifferentiated dung,
and both adults were found near to it.
For O. vanderkelleni, on the only occasion when the female was able to com-
plete her nesting, we found a big clump of dung where only three brood-masses
were differentiated. The others, containing several eggs and larvae at various devel-
opmental stages (n = 22), could not be clearly singled out as they were only partial-
ly formed or fused together. On two other occasions, when the female was dis-
turbed by us during one of the periodic checks or died while laying, we found only
an undifferentiated dung cake.
Egg laying (Fig. 2f). The egg was laid vertically inside a small chamber about
0.5 cm in diameter and lined with semi-liquid dung. The commonest case was that
of a single egg placed at one end of the brood-mass (n = 11 in O. belial, n = 16 in
O. anthracinus); on other occasions (n = 3 O. belial, n = 4 O. anthracinus) a single
egg was laid approximately at the middle of a brood-mass. We also found 2 eggs,
one at each end of the brood-mass (n = 5 O. belial, n = 3 O. anthracinus), 3 eggs in

Reproductive biology in Onitis species
101
one brood-mass (n = 2 O. belial, n = 3 O. anthracinus) and once (O. belial) we
found 4 eggs in a line at the end of the brood-mass. When a brood-mass held more
than one egg, the laying often (n = 13) seemed to have occurred within a relatively
long time span, as we found both eggs and larvae, or larvae in different develop-
mental stages, within the same nest. This was always found when females laid eggs
in cakes instead of brood-masses.
The mean number of eggs laid in a single nest was 5.7 1.8 in O. belial and
12.5 2.3 in O. anthracinus. For O. vanderkelleni, the only complete nest we were
able to observe contained 26 eggs, while in two other cases egg laying was inter-
rupted after 2 and 5 eggs had been produced.
We did not observe parental care, and adults always left the nests after the
completion of egg laying.
Larval behaviour. Hatching larvae grew up in almost spherical chambers dug
in the dung; the presence of several larvae in small spaces [as found in O. aygulus
(Fabricius 1781) by SKAIFE (1953), quoted by HALFFTER & EDMONDS (1982)], both in
brood-masses and in cakes, seems to confirm the ability of the larvae to repair
their chambers if they are damaged (KLEMPERER 1982). At the end of larval develop-
ment, pupation occurred within what was left of brood-masses or cakes, in cham-
bers deriving from those used by larvae.
DISCUSSION
As stressed in the introduction, contrary to what occurs in most genera of
coprophagous Scarabaeidae whose reproductive behaviour has been studied, nest-
ing behaviour in Onitis can include a quite wide range of modalities. The three
species we studied in the laboratory are underground nesters. Nesting begins short-
ly after the provision of fresh dung and follows what has been defined as the “tun-
neler” tactic (SATO 1998a, 1998b).
In O. vanderkelleni, nesting couples invest little in the building of elaborated
nests, as they seem to use mostly undifferentiated cakes. On the other hand, they
invest more resources in the laying of a relatively large number of eggs. This is not
new in Onitis and has been found, for instance, in the Afrotropical species O. aygulus
(cf. SKAIFE 1953). The use of the cake as a definitive location for the eggs is rare or
absent in O. belial and O. anthracinus. The preparation of independent brood-
masses, with eggs laid at regular spaces within them, or just one in a single brood-
mass, seems to reduce both spatial and trophic competitions. This tactic requires
greater energy investment in the building of the nest, but allows a reduction of the
number of eggs laid. O. belial does not seem to conform strictly to this behavioural
scheme, while O. anthracinus, O. westermanni Van Lansberge 1886 and other species
whose behaviour is known (HALFFTER & EDMONDS 1982) appear to adopt it quite
rigidly. The discovery of a nest of O. belial in which the brood-masses were located
inside a dung clump seems to corroborate the hypothesis of KLEMPERER (1982) that
brood-masses can, at least sometimes, be made by digging inside a large compact
structure (cake), previously brought under the soil surface, and subsequently filling
the holes in it with other dung brought from the surface. Moreover, our observations
on the behaviour of O. belial seem to confirm what we previously hypothesised, i.e.,
that the shaping of brood-masses follows the preparation of the cake and egg laying.

102
C Palestrini et alii
Table 1.
A comparison of life history characteristics in two tribes of Scarabaeidae.
Tribe
Nesting
strategy
“Cakes”
built
Brood-
masses
Brood-
balls
Parental
care
Adults
stridulate
Onitini
(Onitis, Bubas)
Tunneler
Tunneler
Yes
No
Yes
No
No
No
No
Coprini
(Copris, Litocopris,
Yes
Yes
Yes
Synapsis, Heliocopris)
It seems unlikely that this nesting behaviour is related to that adopted by the
tribe Coprini, which is similar to Onitini only in that they both share a tunneler
nesting technique, which is however also found in other tribes of Scarabaeidae
(HALFFTER & EDMONDS 1982). Onitini show rather wide variation in their nesting
behaviours, which can vary in the same species according to ecological factors such
as soil type (ROUGON & ROUGON 1982); in contrast the Coprini (Table 1) have com-
plex but rather stereotyped nesting: they are subsocial, prepare brood balls, and
have highly dependent larvae requiring parental care in order to achieve the adult
stage (HALFFTER & EDMONDS 1982). The female usually stays in the nest until the
emergence of the young, adopting a costly strategy that causes a strong loss of
weight and fat and ovariole resorption (HUERTA & HALFFTER 2000).
Detailed studies on a larger number of species will allow us to understand
more clearly the nesting behaviour of Onitis. However, it seems to be more varied
than what was hypothesised by HALFFTER & EDMONDS (1982) in their pattern I nest-
ing behaviour, especially referring to the preparation of the cake. EDWARDS &
ASCHENBORN (1987) proposed an evolutionary pathway linking five patterns of nest-
ing in Onitis. None of the species considered by these authors utilize big masses of
dung (cakes) to lay their eggs, as we report here for three species. Moreover, con-
trary to what seems to occur in the species studied by EDWARDS & ASCHENBORN, in
our studies different individuals of the same species were able to adopt different
nesting tactics.
The nesting behaviour of Onitis species seems not to be a preliminary and
more primitive stage of that of Coprini as suggested by some authors (CHOBAULT
1922, PAULIAN 1941). Contrary to what has been hypothesised by the same authors
for other Onitis species, we never found real brood balls in the nests.
Reproductive behaviour in the Onitini seems characterised by a good ability
to respond to environmental factors. They are coprophagous and can bury large
quantities of dung [about 5 times as much as the Coprini (KLEMPERER 1982)] in a
short time, thus avoiding surface competition with other coprophagous species.
Moreover, their nesting behaviours are not rigidly followed, as they can lay a large
number of eggs in the cake or give a higher level of protection to the larvae by
preparing brood-masses, which however determine a lower output of eggs. Finally,
Onitis larvae are autonomous in the building of the larval and pupal chambers, and
can repair them in case of necessity: in this way, nesting adults are freed from cost-
ly parental care and can leave the nest and repeat the nesting sequence elsewhere.

Reproductive biology in Onitis species
103
ACKNOWLEDGEMENTS
We are indebted to Prof. A. Rolando and Dr P. Laiolo, University of Turin, Italy, for col-
lecting in Morocco the individuals of O. belial studied in this work.
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