Studies on the occurrence of true spiders as natural enemies in many Egyptian fields

Abstract

True spiders represent one of the most important natural predatory species in Egyptian fields. In this work, common true spiders were surveyed in wheat, cotton and maize fields, and were counted weekly by using the direct method. For evaluating the feeding consumption of true spiders, five feeding cases were tested (as preys). These cases were: eggs of Ephestia kuehniella, eggs of Phthorimaea operculella, one day eggs and larvae of E. kuehniella, larvae of E. kuehniella and P. operculella and larvae of E. kuehniella only. Results obtained revealed that, the highest average daily consumption for each spider was recorded in case of feeding on eggs of P. operculella. While, the longest survival period was recorded in case of feeding on larvae of E. kuehniella.

Full text

Studies on the occurrence of true spiders as natural
enemies in many Egyptian fields
Amira A. Ibrahim, Souad A. Shairra *, Iman F.S. El-mahdi
Biological Control Research Department, Plant Protection Research Institute, Giza, Egypt
Received 15 August 2011; accepted 20 October 2011
Available online 27 August 2012
KEYWORDS
True spiders;
Biological control;
Feeding consumption
Abstract True spiders represent one of the most important natural predatory species in Egyptian
fields. In this work, common true spiders were surveyed in wheat, cotton and maize fields, and were
counted weekly by using the direct method. For evaluating the feeding consumption of true spiders,
five feeding cases were tested (as preys). These cases were: eggs of Ephestia kuehniella, eggs of
Phthorimaea operculella, one day eggs and larvae of E. kuehniella, larvae of E. kuehniella and P.
operculella and larvae of E. kuehniella only. Results obtained revealed that, the highest average daily
consumption for each spider was recorded in case of feeding on eggs of P. operculella. While, the
longest survival period was recorded in case of feeding on larvae of E. kuehniella.
ª2012 The Egyptian German Society for Zoology. Production and hosting by Elsevier B.V. All rights
reserved.
Introduction
True spiders (Araneae) represent by far the largest order of the
arachnids, with about 35,000 species known worldwide. All are
carnivorous predators with powerful fangs, called chelicerae,
which are used to bite and crush the prey and to inject venom.
However, Wise (1993) stated that spiders are generalist feeders
that attack insects and other arthropods. They are even more
strictly carnivorous that have many other tasks of primarily
predacious invertebrates such as carbide beetles. He added that
patent neurotoxins enable spiders to kill preys rapidly. Victims
usually are smaller than are similar in size to the spider, but
many spiders subdue preys several times their own mass. Many
of the spiders commonly found in Egyptian fields, particularly
wolf spiders (members of the family Lycosidae), Philodromi-
dae and Scytodidae are considered beneficial natural enemies.
Many authors who are related to biological control field of in-
sect pests mentioned true spiders as important predators with-
in their works of survey. Many biological aspects concerning
true spiders were previously studied. For example, Jones
(1984) mentioned that spider eggs are approximately spherical
and about 1 mm in diameter. They are laid in compact mass
and covered to a greater ascent with silk, forming a sac. The
eggs are pale yellow, brown and may be bright green. The
number of eggs laid depends on the size of the female. On
the other hand the size of eggs depends on the species of the
spider. Also, in Egypt, El-Mehalawy (1988), Rahil (1988),
Ghabbour et al. (1999) and Rakha et al. (1999) studied some
biological aspects of many spider families in some different
Egyptian governorates.
The present work was conducted to study the occurrence of
true spiders in wheat, cotton and maize fields in Giza and Al-
Fayoum governorates. Surveying of common true spiders was
done in the three fields included: wheat (January–April),
*Corresponding author.
E-mail address: s_shairra_egy@yahoo.com (S.A. Shairra).
Peer review under responsibility of The Egyptian German Society for
Zoology.
Production and hosting by Elsevier
The Journal of Basic & Applied Zoology (2012) 65,1–3
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2090-9896 ª2012 The Egyptian German Society for Zoology. Production and hosting by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jobaz.2011.10.001

cotton (May–September) and maize (May–September) during
2009 and 2010 seasons. Moreover, laboratory studies were
made to evaluate the feeding capacity of true spiders on some
different preys and their preference to such preys, in order to
evaluate more accurately their role in affecting the population
densities of these pests.
Materials and methods
Manual picking of true spiders
One of the easiest ways to get large numbers of spiders is by
using a sweeping net than picking the spiders from among
the insects gathered with them by hand. Specimens are trans-
ported back to the laboratory alive or dead. ‘‘Pit-fall’’ traps
are set in order to keep specimens from eating each other
and to prevent decomposition of dead ones, some ethylene gly-
col was poured to a depth of about one inch in the trap. In this
way specimens that fall into the trap are killed and preserved.
Laboratory rearing of true spiders
Spiders have cannibalistic habits between each other; there-
fore, live specimens were kept each in its own container at
the laboratory for rearing purpose. The spiders were reared
according to the technique described by Ibrahim et al. (2003).
Survey of true spiders in many Egyptian fields at Giza and Al-
Fayoum governorates
Survey of the common true spiders found in wheat, cotton and
maize fields, was done in the Giza and Al-Fayoum govern-
orates, during the 2009 and 2010 seasons, where 100 plants
either for wheat or cotton and 25 plants for maize, were weekly
investigated and counted (early in the morning).
Identification of true spiders
In most cases the families are easy to distinguish in the field by
position and number of eyes, overall shape, length of legs, and
form of spinners. In the laboratory it is easy to separate the
kinds of true spiders which are morphologically similar and gi-
ven a code number for each. Then, they were kept in a mixture
of 70% alcohol and 5% glycerol until their identification.
Amount of food consumed
For studying food consumption of the lycosid spider, five sets
of experiments were done. Newly immediately hatched juve-
niles (20–30 spiderlings) from the egg sacs introduced to the
laboratory or the small juveniles over the back of the intro-
duced females, were isolated individually in glass tubes, and
were provided daily with certain number of preys. In the first
set of experiment eggs of Ephestia kuehniella were used for feed-
ing the juveniles. In the second set eggs and larvae of E. kuehni-
ella (2–3 stages) were used. In the third set only larvae of
E. kuehniella were used in each experiment. In the fourth set,
larvae of E. kuehniella in addition to larvae of Phtharimaea
operculella were used. In the last set eggs of P. operculella were
only used. In case of feeding the spiders on eggs only, 30 eggs
were offered in each of the first two days, then they were
increased gradually up to 150 eggs, starting the third day. In
case of larvae as food, the second stage was offered at first
for 2 days then the third stage was offered for the rest of the
days. Only one larva was offered on the first 2 days then the
number was increased to 3 once daily till the end of the
experiment.
Results and discussion
Survey of true spiders in many Egyptian fields at Giza and Al-
Fayoum governorates
Table 1 shows the different species of true spiders that were re-
corded in wheat, cotton and maize fields in both Giza and Al-
Fayoum governorates.
The same findings were also shown by Ibrahim et al. (1975),
in the same fields.
In wheat fields the total numbers of spiders within wheat
fields increased in Giza from 4, 8, 80 to 160 during months
of growing and counting such as January, February, March
and April.
Spiders increased in number with warm conditions or due
to temperature and plant growth. A similar increase in Al-
Fayoum was recorded as 12, 16, 216 and 328 (Table 2). Ibra-
him and Fayad (1980), found that, true spider is the most tol-
erant predator to chemical pesticides in Egypt.
In cotton fields (Table 3) the counting numbers increased in
Giza to be 120 in May, 160 in June, reaching the maximum of
290 in July then decreased gradually in August to 236 and 174
in September. This reduction in numbers may be due to insec-
ticide use in cotton fields. The same trend in numbers was clear
in Al-Fayoum which was 260 and 340 in June and July then
decreased to 220 and 189 in August and then 189 (Table 3).
In Maize fields, the same trend of counting numbers was
found as in cotton fields. In Giza they were in the correspond-
ing months 60, 107, 200, 330 and 196 and in Al-Fayoum 78,
132, 168, 266 and 178 (Table 4). These findings agree with Ibra-
him et al. (1975, 1979, 2003) and Ibrahim and Fayad (1980).
Evaluation of food consumption of true spiders
As shown in Table 5, the average daily consumption for each
spider was the highest in case of feeding on eggs of P. opercul-
ella, compared to all other tested cases. Moreover, the longest
survival period was in the case of feeding on larvae of
E. kuehniella, compared to all other tested cases.
Under laboratory conditions, the initial number of spider-
lings could not proceed to be adults in most of the cases. This
Table 1 Identification of true spiders in wheat, cotton and
maize fields, in Giza and Al-Fayoum governorates.
Scientific name Family name Host plant
Cheiracanthium sp. Philodromidae Cotton, Maize
Thanatus vaulgaris Clubionidae Wheat, Maize
Wadicosa venatrx (Locus) Scytodidae Maize
Dictyna sp. Dictynidae Cotton, Maize
Thomisus citrin ellus Thomisidae Cotton, Maize
Runcinia sp. Thomisidae Wheat
Paradosa sp. Lycosidae Maize
Singa sp. Araneidae Cotton
2 A.A. Ibrahim et al.

observation may be due to the presuming condition in addition
to this unique laboratory feeding sort which must be unstable
(Ibrahim et al. 1975). The spider consumed the eggs as a star-
vation diet, appropriate food material since the spider could
not survive on such a diet till adult stage in all the cases of
experiment. When eggs were added to the larvae for feeding,
the spider neglected the eggs and consumed the larvae only
as the spider prefers moving preys. It is known that all spiders
have poison glands, these glands open by a pore near the tip of
each chelicerae fang. These glands are cylindrical and are cov-
ered by muscles which contract to expel the venom which is
used by spiders to kill their preys, as a means of defense. Spi-
ders are generalist feeders that primarily attack insects, but
also eat other arthropods including spiders.
In conclusion, for biological control purpose, it is impor-
tant to know the natural role of true spiders as a component
of the ecosystem (predatory control agents).
References
El-Mehalawy, M.H.M., 1988. Some studies on spider families of Al-
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populations associated with different crops in Menoufia Gover-
norate, Egypt. Egypt. J. Agric Res. 77 (3), 1163–1179.
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Table 2 Total number of true spiders recorded in wheat fields/season, in both Giza and Al-Fayoum governorates.
Governorate Number of true spiders on 100 wheat plants/ season.
January February March April
Total Aver. Total Aver. Total Aver. Total Aver.
Giza 4 1 8 2 80 20 160 40
Al-Fayoum 12 3 16 4 216 54 328 82
Table 3 Total number of true spiders recorded in cotton fields/season, in both Giza and Al-Fayoum governorates.
Governorate Number of true spiders on 100 cotton plants/season
May June July August September
Total Aver. Total Aver. Total Aver. Total Aver. Total Aver.
Giza 120 30 160 40 290 72.5 236 59 174 43.5
Al-Fayoum 201 50.3 260 65 340 85 220 55 189 47.5
Table 4 Total number of true spiders recorded in maize fields/season, in both Giza and Al-Fayoum governorates.
Governorate Number of true spiders on 25 maize plants/season.
May June July August September
Total Aver. Total Aver. Total Aver. Total Aver. Total Aver.
Giza 60 15 107 26.8 200 50 330 82.5 196 49
Al-Fayoum 78 19.5 132 33 168 42 266 79.5 178 44.5
Table 5 Average daily food consumption of the lycosid sp. true spiders fed on eggs and/or larvae of either E. kuehniella or
P. operculella.
Feeding case Initial No. of newly hatched
spider/experiment
Spider survival/days Average daily
consumption/spider
1. Eggs of E. kuehniella 20 6 (4–8) 28.4
2. Eggs of P. operculella 20 10 (2–12) 38.2
3. One day eggs + larvae of E. kuehniella 20 85 (12–91) 5.1
4. Larvae E. kuehniella +P. operculella 30 160 (18–68) 4.2
5. Larvae of E. kuehniella 30 176 (8–91) 9.3
Studies on the occurrence of true spiders as natural enemies in many Egyptian fields 3