16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Spider (Araneae) Species Activity, Crop Type and Management
Factors in an Extensive Plot Trial
Eyre, M.D.1, Shotton, P.N.2 & Leifert, C.3
Key words: Spiders, Organic farming, Fertiliser, Crop protection
Abstract
Spider species activity in five crop types, with organic and conventional fertility and
crop protection management, was assessed using pitfall traps in 2005. Significant
differences in activity between crop types were seen with 16 species, with 14 most
active in grass/clover and 12 least active in vegetable plots. Within crops there were
20 significant responses to fertility, with 16 more active in conventional plots. Crop
protection management produced four significant models, with three preferences for
organic management. Small linyphiid species showed a distinct preference for the
densest vegetation on conventionally fertilised plots, whilst the larger lycosid species
were more active on the more open organic plots. In general, there was more activity
in conventionally managed crops, in contrast to other reports.
Introduction
Agricultural management has a considerable effect on the activity of spiders (Cole et
al., 2005) and Fuller et al. (2005) found more spider activity in organic wheat than
conventional. However, crop type had more effect on activity than management
system (Booij & Noorlander, 1992). Eyre et al. (2007) found that fertility rather than
crop protection management had considerably more influence on the activity of
beneficial invertebrates and the Nafferton Factorial Systems Comparison Experiment
provides an opportunity to assess spider species activity at the plot scale. A number of
organically and conventionally managed crop types were surveyed.
Materials and methods
The Nafferton Factorial Systems Comparison Experiments consists of 128 plots (24 x
12 m) in an area converted to organic management in 2003. In 2005 the plots
contained wheat, barley, beans, vegetables (potatoes, cabbage, onions, lettuce,
carrots) and grass/clover. The 64 conventionally managed plots were treated with
inorganic fertiliser and sprayed with herbicide, fungicide and pesticide where
appropriate. The 64 organic plots were fertilised with compost and no sprays were
used. Each plot was sampled using five pitfall traps with saturated salt solution
containing a small amount of strong detergent as preservative. The traps were set in
the first week of May 2005 and five monthly samples were generated. Samples were
sorted in the laboratory and spiders identified to species. Data analyses with 29 of the
57 species recorded were used in linear mixed-effects models in the R statistical
environment (R Development Core Team, 2007), as in Eyre et al. (2007).
1
Nafferton Ecological Farming Group, University of Newcastle Upon Tyne, Nafferton Farm,
Stocksfield, Northumberland, NE43 7XD, UK; Mick.Eyre@nefg.co.uk
2
As Above, Peter.Shotton@nefg.net
3
As Above, Carlo.Leifert@nefg.net
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Results
Sixteen species produced significant responses with the crop models and the mean
numbers recorded from each crop is shown in Tab. 1. The mean number of most
species was low, with only four species having means of over 10 in a crop. Fourteen
species were most active in grass/clover, with 12 having the least activity in the
vegetable plots. There was more activity of the abundant species in the cereal crops
than in beans.
The significant responses of species to fertility or crop protection within crop types and
the means showing preferences for organic or convention plots are shown in Tab. 2.
Two species produced significant responses in grass/clover with fertility, one preferred
conventional plots, the other organic. O. retusus preferred bean plots with
conventional fertility whilst two Pardosa species were more active in bean plots with
organic crop protection. Four linyphiid species produced significant responses to
fertility in wheat, all preferring conventional plots. Seven of the 10 species giving a
significant response to fertility in barley liked conventional management with more of
three species in organic plots. There was more activity of three linyphiid species in
conventionally fertilised vegetable plots, with one species preferring conventional crop
protection and another organic.
Tab. 1: Spider species giving a significant response to crop type and the mean
number recorded from plots in the five crop types.
Species
Grass/
Clover
Bathyphantes gracilis
6
Centromerita bicolour
2
Erigone atra
152
Erigone dentipalpis
56
Leptorhoptrum robustum 2
Lepthyphantes tenuis
24
Lepthyphantes
3
zimmermanni
Milleriana inerrans
4
Oedothorax fuscus
7
Oedothorax retusus
1
Pardosa agricola
3
Pardosa amentata
4
Pardosa pullata
2
Pachygnatha clercki
0
Pachygnatha degeeri
14
Robertus neglectus
1
** significant for P<0.01
*** significant for P<0.001
Beans Wheat
Barley Vegetables
2
2
60
17
2
14
1
2
1
87
17
1
15
1
3
1
84
24
1
15
1
0
0
25
10
0
14
2
***
**
***
***
**
***
***
2
3
1
3
4
0
1
4
2
3
1
1
2
2
0
0
4
1
4
5
0
3
2
1
1
6
1
2
2
0
1
2
0
0
2
0
**
***
**
**
**
***
***
***
**
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Tab. 2: Spider species giving a significant response to either fertility or crop
protection within each crop type, together with mean numbers recorded from
plots with organic and conventional management.
Crop and species
Grass/clover
Erigone atra
Pardosa agricola
Beans
Oedothorax retusus
Pardosa agricola
Pardosa amentata
Wheat
Dicymbium nigrum
Erigone atra
Leptorhoptrum robustum
Milleriana inerrans
Barley
Bathyphantes gracilis
Erigone atra
Erigone dentipalpis
Leptorhoptrum robustum
Lepthyphantes tenuis
Milleriana inerrans
Pardosa agricola
Pardosa amentata
Pachygnatha degeeri
Robertus neglectus
Vegetables
Diplostyla concolor
Erigone atra
Milleriana inerrans
Ostearius melanopyrgius
Robertus neglectus
* significant for P<0.05
** significant for P<0.01
*** significant for P<0.001
Factor
Organic
Conventional
Fertility
Fertility
145
4
168
3
*
***
Fertility
0
Crop protection 4
Crop protection 5
1
2
3
*
*
*
Fertility
Fertility
Fertility
Fertility
0
59
0
2
1
117
2
4
***
**
**
**
Fertility
Fertility
Fertility
Fertility
Fertility
Fertility
Fertility
Fertility
Fertility
Fertility
2
60
20
0
12
1
5
3
7
1
4
107
27
1
18
6
0
1
5
2
**
***
*
*
***
***
***
*
**
*
Crop protection
Fertility
Fertility
Fertility
Crop protection
0
19
1
0
1
1
31
3
2
0
*
***
*
*
*
Discussion
One obvious observation from the results was that although 57 species were
recorded, most were trapped at very low numbers. However, the two most abundant
species, E. atra and E. dentipalpis, were the most abundant species on Scottish
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
agricultural land (Downie et al., 2000) and also on the plots sampled here. Weibull &
Östman (2003) found differences in spider activity between cereal and grassland
crops and there were considerably more activity in grass/clover plots for most species,
with the least on the vegetable plots. Within crops there were 20 significant models
with fertility, with more activity of 16 species in conventional plots. There appears to be
a difference between small, linyphiid species, preferring denser vegetation on
conventional plots, and larger lycosid species, favouring the more open organic plots.
Of the four significant responses to crop protection, three showed preferences for
organic management, possibly related to increased weed cover (Sunderland & Samu,
2000) with no herbicide application. However, in general most activity was in the
conventionally managed crops, a contrast with other reports (Schmidt et al., 2005).
Conclusions
Vegetation architecture is known to affect spider activity and fertility and crop
protection management can change crop structure. In the plots surveyed there was
more spider activity in the more densely vegetated conventionally managed crops.
Acknowledgments
The authors gratefully acknowledge funding from the European Community financial
participation under the Sixth Framework Programme for Research, Technological
Development and Demonstration Activities for the Integrated Project
QUALITYLOWINPUTFOOD, FP6-FOOD-CT-2003- 506358.
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