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Iheringia, Série Zoologia, Porto Alegre, 103(4):388-392, 31 de dezembro de 2013
388
The diet of the black widow spider Latrodectus mirabilis (Theridiidae)
in two cereal crops of central Argentina
Gabriel Pompozzi1, Nelson Ferretti2, Leonela Schwerdt1, Sofía Copperi1, Adriana A. Ferrero1 & Miguel Simó3
1. Laboratorio de Zoología de Invertebrados II, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, San Juan 670 (8000), Bahía Blanca, Argentina.
(gabrielpompozzi@conicet.gov.ar; leo_vane10@hotmail.com; ; aferrero@uns.edu.ar)
2. Centro de Estudios Parasitológicos y de Vectores - CEPAVE (CCT-CONICET) (UNLP), La Plata, Argentina. (nferretti@conicet.gov.ar)
3. Sección Entomología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay. (simo@fcien.edu.uy)
ABSTRACT. The spider Latrodectus mirabilis (Holmberg, 1876) is commonly found in cereals crops of central Argentina. We studied its
documents the diet of L. mirabilis webs during the
last phenological stages of both cereal crops. The prey composition was variable but the spiders prey mainly on ants (Formicidae, Hymenoptera),
Latrodectus spiders
around the world.
KEYWORDS. Diet composition, capture rate, polyphagous predator, South America.
RESUMEN. Dieta de la viuda negra, Latrodectus mirabilis (Theridiidae) en dos cultivos de cereales del centro de Argentina. La araña
Latrodectus mirabilis (Holmberg, 1876) se encuentra comúnmente en cultivos de cereales del centro de Argentina. Se estudió la composición
de la dieta a campo y la tasa de captura sobre hormigas cortadoras negras a laboratorio. Este estudio documenta el primer registro de la dieta de
L. mirabilisL. mirabilis en las
últimas etapas fenológicas de ambos cultivos. La composición de presas fue variable, pero las arañas se alimentaron principalmente de hormigas
captura, registramos una alta tasa de captura de hormigas al inicio de las mismas, capturando la mitad de las hormigas en las primeras cuatro
horas. En resumen, reportamos una dieta polífaga en esta especie de araña en los cultivos de trigo y avena. El ítem presa más importante fueron
las hormigas, resultados similares a los encontrados en otras especies del género Latrodectus.
PALABRAS-CLAVE. Composición de dieta, tasa de captura, predador polífago, America del Sur.
Spiders are relevant terrestrial predators and also
located on the top of many invertebrate food webs. They
are abundant and ubiquitous showing diverse feeding
habits (, 1993). Usually, terrestrial food webs have
a high diversity of generalist predators, among which
spiders are very common ( & , 1996).
Indeed, they are among the most abundant natural
predators registered in agroecosystems ( &
, 1987; & , 2003).
Knowledge of prey items and rates of predation
is relevant to evaluate the effect of predators on prey
populations and mainly in estimating the potential
effectiveness of a predator as an agent of biological
control ( & , 1990). Most of the spiders
are polyphagous predators and are capable to feed on
many insects including major crop pests ( &
, 1988). Polyphagy provides access to a variety of
nutrients that usually are not obtained through a single
prey source, which could enhance growth rates and
juvenile survival ( & , 1999). Nevertheless,
few species are specialist of a particular prey, where the
,
2012; et al.
predation on pest species on agroecosystems by spider
species belonging to the Theridiidae ( &
feeding behavior involving Latrodectus species all over
the world (, 1981; , 1982;
et al., 1988; & , 1999;
& -, 2002; et al.,
2008; et al., 2011; , 2011). However,
in Argentina, studies on diet composition and prey
selection are scarce; highlighting that from Thomisidae,
species in soybean and alfalfa crops ( et al., 2006;
et al., 2009; & ,
2011). Nonetheless, these studies did not involve diet
selection or consumption rate at the laboratory or
knowledge about the natural diet of spiders associated
with agroecosystems is unknown.
Latrodectus mirabilis (Holmberg, 1876) is a web-
building spider with wide distribution on central and
southern Argentina, which constructs irregular webs at
ground level, and in the cereal crops it lives between
grasses and frequently at the entrance of small mammal
crevices (, 1980). There is abundant in cereal
crops, like wheat and oat at southwestern Buenos Aires
Province, central Argentina (pers. observ.). However, the
only data available of diet for Latrodectus species in this
country are based mainly in few observational records
(, 1979; , 1980). This previous studies
indicate that this species preys on the ants Acromyrmex
Pompozzi et al.
Iheringia, Série Zoologia, Porto Alegre, 103(4):388-392, 31 de dezembro de 2013
389
and Camponotus but its degree of spider myrmecophage
is still unknown (, 1980; , 2012).
Therefore, the main goal of this study was to
determine the feeding ecology of the black widow
spider in two different crops of central Argentina. The
on leaf-cutting ants (Acromyrmex lundii, Formicidae).
We chose this prey species because the ants are the most
abundant prey item of Latrodectus spiders in the crops
some studies that mention certain preference for this type
, 1979). Moreover, Acromyrmex
ants cause damage on cereal crops of central Argentina,
e.g. sorghum ( et al., 2009).
MATERIAL AND METHODS
The
at southwestern Buenos Aires province, Argentina
pesticides during the last 30 years. Both crops were
planted in August 2012 (winter in southern hemisphere)
and harvested in December of 2012 (beginning of
summer in southern hemisphere). The sowing method
was conventional, plowing before planting. The
study site is located in an area of temperate climate
annual average rainfall of 670 mm (obtained from the
dates during November-December (spring) period
corresponding to the last phenological stages of crops.
Each sample date involved four collectors in active
searching during one hour (between 10 am to 3 pm) for
Latrodectus mirabilis webs on each crop. When a web
was found, we collected all prey items that had been
captured by the spiders. This was achieved by picking the
preys off the webs with specialized forceps. Specimens
prey items at the order/family level. Also, we collected
spiders (deposited then in 70% ethyl alcohol) hanging
abdomen (, 1981). Voucher specimens are
deposited in the arachnological collection of Laboratory
of Invertebrates II, Universidad Nacional del Sur, Bahía
Blanca, Argentina (Nelson Ferretti). We computed
presented by ij
pikij
2 ik
2),
where pij
and pik represents the proportion of prey items
from wheat (pij) and oat (pik). Values range between 0 (no
the degree of variation of prey composition using
Ai
2)
i is the proportion of prey items
from prey type i, and n is the total number of prey types
(
values close to 0 indicating that a predator consumes
few prey types in high proportion, and values close to 1
indicating that all prey are consumed in equal proportion.
We calculated BA
values for each crop and for the whole
study. Moreover, we calculated BA value for each stage
of spider. We collected 20 adult females of Latrodectus
mirabilis
Argentina, in January 2013. We housed the spiders
metallic rods as support for spider webs. We used a 12h
light/dark cycle. The room temperature during breeding
with cockroaches, Blatella germanica Linnaeus, 1767,
The prey species used in this study was the leaf-cutting
ant, Acromyrmex lundii Guérin-Menéville, 1838. We
A. lundii) neighboring
university courtyard on the same day that we carried
plastic recipient holding one adult female of L. mirabilis
with 10 individuals of A. lundii, and a control recipient
introducing the ants into the spider recipient and ended
spider as the dead ants in the control for foreign causes
(Nd-Nm d0-Nt represent the number of
capture preys by the spider; N0 is the initial number of
preys; Nt
Nm0c-Ntc is the number of dead preys in control; t is
the time in hours.
RESULTS
immature females and 101 juveniles of undetermined
development (, 1981). In total we collected
L. mirabilis. We found
nine arthropod orders in the webs of L. mirabilis in both
spiders prey mostly on ants (Formicidae, Hymenoptera),
which represented more than 86% of the total (Tab.
to 13 item preys of 77 spider’s webs (Tab. II). The
most abundant item prey was Formicidae whose reach
80.9%, follows by aphiids with 8.6% (Tab. II). In the
Formicidae, Aphididae and Coleoptera were the most
the spiders prey upon natural enemies as Staphylinidae
The diet of the black widow spider Latrodectus mirabilis (Theridiidae)...
Iheringia, Série Zoologia, Porto Alegre, 103(4):388-392, 31 de dezembro de 2013
390
Tab. I. Latrodectus mirabilis
number of spider webs).
Prey item
Insecta
Formicidae 100.0 88.0 90.1 83.8
Aphididae 0 0 3.9
Coleoptera 0 7.0 2.8
Hemiptera 0 0 0 1.3 1.7
Hymenoptera 0 0 0 1.3 0.8
Diptera 0 0 0 1.1
Lepidoptera 0 0 1.3 0 0.2
Orthoptera 0 0 0 0
Psocoptera 0 0 0 0 0.2
Arachnida
Acari 0 0 0 0 0.3
Araneae 0 0 1.3 0 0.2
Total 100.0 100.0 100.0 100.0 100.0
(Coleoptera), some Hymenoptera (micro-parasitoids)
and other spiders (Araneidae and Lycosidae) in low
numbers (Tab. II). The most common preys in the two
crops were ants and aphiids, reaching 92.6% of the
overall diet breadth of L. mirabilis at the study site in
BA). The BA
(females) to 0.097 (males). The BA values for each spider
males) and 0.031 (juveniles). Females showed a zero
The BA
We registered a high proportion of ants captured by
specimens of L. mirabilis consumed all ants during the
the initial time, the C value was 0.83 prey/hour, being
DISCUSSION
In the present study, some aspects of feeding
ecology of Latrodectus mirabilis from two cereal crops
of central Argentina are highlighted. We found a varied
arthropod orders were found in the webs of L. mirabilis in
and the spiders obtain their primarily sources of prey
from two insect orders (Hymenoptera and Hemiptera).
From these values, Hymenoptera comprised the majority
of prey catches. Within this order, ants were the more
relevant item prey of this spider species. Particular prey
of many polyphagous spider species (, 1999),
as was found in this study. Other Latrodectus species
across different habitats have a polyphagous diet,
and has been reported that the prevalent prey type is
Coleoptera ( & -,
2002; & , 2011).
Nevertheless, some Latrodectus spiders like
L. pallidus (Pickard-Cambridge 1872) from Israel
and L. mactans
also important predators of Hymenoptera such ants
( & et al., 1988),
as was observed in this study. The diet of L. mactans
to the L. mirabilis
of the total prey consumed ( et al., 1988).
L. mirabilis, like other
theridiid spiders, are adapted primarily for the capture
of arthropods that crawl on the ground (
the ants represented the most abundant insects in both
diverse than diet of immature males, immature females
and adults, preyed on all item preys registered. We
found intra-guild predation, but the spiders represent
a low percentage in the diet of L. mirabilis, similar to
that found in other species of the genus ( et al.,
1988;
in diet composition between spider that inhabit wheat
overlap of preys captured by L. mirabilis between both
available preys.
The low value of the BA
the spiders prey upon a few arthropod orders in high
proportion and many orders in small quantities. This
low value showed that the diet of L. mirabilis could be
a particular environment (, 1999). However,
their diet is polyphagous, because the spiders prey upon
a varied item prey but with a high proportion of one item
(ants). Nevertheless, the black widow spider does not
actively select its prey, but has to wait for them to become
Pompozzi et al.
Iheringia, Série Zoologia, Porto Alegre, 103(4):388-392, 31 de dezembro de 2013
391
ensnared by the hunting threads of the web. As a result
from this passive hunting mode, the prey captured by the
( & , 1987). As mentioned above,
ants were very abundant in both crops, so they were the
the low value of BA. Arguably, spider’s diet breadth may
depend on several factors, including intrinsic factors
such as prey-capture behavior and foraging mode,
ecology, and combinations of them (, 1990). Prey-
predators, are reluctant to ant predation, because ants
are generally aggressive some are venomous and most
, 2012). However, theridiid
spiders such as Latrodectus typically capture prey by
‘combing’ sticky silk around them with their back legs
to immobilize the prey ( & , 2008). This
foraging technique allows capturing large or potentially
harmful prey such as ants (, 1987).
because they are large and with huge mandibles and
spines, we registered a high proportion of ants captured
The black widow spiders prey upon ants with no major
problems, and captured a high proportion of ants in the
physiological events in the life cycle of the spider (e.g.
molt), climatic conditions and availability and type of
preys ( et al et al
estimated that a spider in agroecosystems captured
that the same species feed at a higher rate when prey
is offered ad libitum ( & , 1986). This
the results obtained in this study could allow as thinking
in L. mirabilis as an important biological control agent
for ants. Although, it is necessary to develop more
differences in the capture rate.
The diet of L. mirabilis has not been previously
described in detail (, 1980). Thus, the results
species. Furthermore, the data presented in this study
represent further the diet of juvenile, because more
than 70% of the webs registered belong to immature
stages. This is due to the phenological development of
crops studied. Wheat and oat are winter crops, and in
late spring and early summer are harvested. Adults of L.
mirabilis appear when the crops are mature, just before
the harvested, and because of that we have low data of
adult individuals (, 1981).
include the assessment of the spiders’ prey capture rates
as well as the evaluation of seasonal population densities
of spiders and their prey, since Latrodectus mirabilis
comprise a potentially useful species for pest control in
cereal crops of central Argentina.
Acknowledgements. Thanks to Dr. Rodrigo Tizón for their
CONICET for doctoral fellowships, and NF also thanks to CONICET
for their postdoctoral fellowship. Financial assistance was provided by
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Hymenoptera
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Others 1.1
Coleoptera
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Curculionidae 0.2 0.2
Others 1.8
Hemiptera
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Araneae
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The diet of the black widow spider Latrodectus mirabilis (Theridiidae)...
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