Spiders have been collected over a period of ten years in five
cotton-growing areas in South Africa. Thirty-one families, represented by 92
genera and 127 species were recorded. The Thomisidae were the richest in species
(21) followed by the Araneidae (18) and Theridiidae (11). The most abundant
species were Pardosa crassipalpis (Lycosidae), Enoplognatha
sp. (Theridiidae), Eperigone fradeorum (Linyphiidae), and
Misumenops rubrodecoratus (Thomisidae). The wandering spiders
constituted 61.5% of the spider fauna collected and the web-builders 38.5%.
Spiders are common and occur in high numbers in cotton fields and prey on a
variety of cotton 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. Read more in: Dippenaar-Schoeman, A.S., Van den
Berg, A.M. & Van den Berg, A. 1999. Spiders in South African cotton
fields: species diversity and abundance (Arachnida: Araneae). African Plant
Protection 5: 93-103. [ SpidersSAcottonfieldsspeciesdiversityANDabundance.pdf] Van den Berg, A.M., Dippenaar-Schoeman, A.S. &
Schoonbee, H.J. 1990. The effect of two pesticides on spiders in South
African cotton fields. Phytophylactica 22: 435-441. [ The effect of two pesticides on spiders in South African cotton fields.pdf] Van den Berg, A.M. & Dippenaar-Schoeman, A.S.
1991. Spiders, predacious insectsand mites on South African cotton.
Phytophylactica 23: 85-86. [ 1991.Cottonspiderspredaciousinsectsandmites.pdf] Spiders in Bt-cottonBt-cotton, containing and expressing genes from the soil
bacterium Bacillus thuringiensis, is specifically toxic to lepidopteran
larvae but little is known about the impact on predators such as spiders. A
survey to determine the effect of Bt-cotton and endosulfan applications on
spider populations was conducted over two cotton growing seasons (2001/2002 and
2002/2003) at Marble Hall, South-Africa. Plant dwelling spiders (n=227) were
counted while scouting the plants, but not identified during both seasons.
Ground dwelling spiders (n=3775) were collected with pitfall traps (n=180)
during both seasons and identified to species level. The ground dwellers
were represented by 21 families, 49 genera and 54 species. During the first
season a total of 2431 spiders were collected from the pittraps: 945 spiders
from Bt-cotton and 1486 from non Bt-cotton (control) plots, while in the second
season a total of 781 were collected, 416 from Bt-cotton and 365 from the non
Bt-cotton (control) plots. A total of 563 spiders were collected from the
endosulfan sprayed non-Bt-cotton fields during the second season. The Lycosidae
(n=2359) comprises 62.5% of all spiders collected in the pittraps, followed by
the Theridiidae (n=757) with 20.1% and Linyphiidae (n= 342) with 9.1%.
Steatoda erigoniformis (Theridiidae) (n=744) were the most abundant
species representing 19.7% of all the spiders collected followed by Pardosa
clavipalpis (Lycosidae) (n=624) with 16.5%, an undetermined Trabea
sp. (Lycosidae) (n=592) with 15.7% and another lycosid Pardosa
crassipalpis (n=543) with 14.4%. Neither Bt-cotton nor the application of
endosulfan had apparent negative effects on ground or plant dwelling spiders in
the field. Spiders should therefore be able to continue playing a role in
biological control in Bt-cotton fields.
Read more
in: Mellet, M.A., Schoeman, A.S. & Dippenaar-Schoeman,
A.S. 2006. The effect of Bt-cotton cultivation on spider populations in
Marble Hall, South Africa. African Plant Protection
12: 40-50. [ The effect of Bt-cotton cultivation on spider populations.pdf] | |  Theridiidae: Enoplognatha sp.
 Lycosidae:
Pardosa sp.
|