Spiders are polyphagous and feed on a variety of available
prey. Predation is not limited to adult insects only, but include the egg,
larval and nymphal stages as well. As predators, spiders have a two-fold
function. Not only do they feed directly on their prey, but their presence
causes indirect mortality. The presence of spiders could disturb larvae who then
drop from the plant and die, while the webs spun over the leaves also seem to
make them less suitable for oviposition and feeding. With increased interest in
non-chemical control strategies, the need to understand the diverse group of
organisms that might play a role in our agro-ecosystems is increasing. It is
predicted that hundreds of potentially useful biological control agents are
still unknown to man. Thus before they can be economically used, these organisms
must be collected, studied and integrated into our information systems.
Therefore surveys of the araneofauna are essential before experimental work
could be carried out. Spiders were collected from 1977-2000 in 10 citrus-producing
areas in South Africa. Thirty-five families, represented by 134 genera and 197
species were recorded. The Thomisidae were the richest in species (28) followed
by the Salticidae (23) and Araneidae (22). The spider species with the widest
range was Pardosa crassipalpis Purcell (Lycosidae) which have been collected
from six of the localities followed by three orb web species, the sac spiders
Cheiracanthium furculatum and a Clubiona sp,
Enoplognatha sp. (Theridiidae), Eperigone fradeorum (Berland)
(Linyphiidae), and Misumenops rubrodecorata Millot (Thomisidae). The wandering spiders constituted 61.5% of the spider fauna
collected and the web-builders 38.5%. Information on guilds, relative
abundance and distribution are provided for each species in an annotated
checklist. Spiders are common and occur in high numbers in citrus orchards and
prey on a variety of citrus pests. Although spiders may be incapable of
controlling major pest outbreaks by themselves their role in a complex predatory
community may be important in regulating pest species at low densities early in
the season and in between peaks of pest species activity. They therefore could
play an important role in keeping pests at endemic levels and preventing
outbreaks. This survey forms part of the South African National Survey of
Arachnida (SANSA) in agro-ecosystems. Collaborators:
Peter Stephen (Citrus International); Dr
M. van den Berg (ARC-Institute for Tropical and Subtropical Crops) Read more:
Dippenaar-Schoeman, A.S. 1998.
Spiders as predators of citrus pests. In: Bedford E.C.G. & Van den Berg,
M.A. (eds). Citrus pests in Southern Africa. Agricultural Research Council,
Nelspruit. Dippenaar-Schoeman, A.S., Van den Berg, A.M. &
Stephens, P. (in preparation). Species in South Africa citrus orchards:
species diversity and abundance (Arachnida: Araneae) Stephen, P.R., Grout, T.G. & Dippenaar-Schoeman,
A.S. 2001. The abundance and distribution of spiders in the South
African citrus ecosystem. Abstract of the 15th International Congress of
Arachnology, Badplaas South Africa p. 164. Van den Berg, M.A., Dippenaar-Schoeman, A.S., Deacon
V.E., Anderson, S.H. 1992. Interaction between citrus psylla,
Trioza erytreae (Hem. Triozidae), and spiders in an unsprayed citrus
orchard in the Transvaal Lowveld. Entomophaga 37(4): 599-608.
[Pdf] | 
Sampling the
citrus orchard
Miturgidae:
Cheiracanthium sp.
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